Crate V5 mods... anyone?

[Tarin]

Yep, i'm one of those who fell for the Crate V-Series blowout sale, at first i bought the V-18, and considered it a good amp, great for the price... sold it after a great offer made to me.
Went back to MF only to find out they were out of stock (also in GC, Sameday, Samash and everywhere).
Made my homework on the V5, and althought it had bad reviews i went for it thinking "how bad could it be" and "even if it's that bad, somebody will come out with mods for it".

Well, the amp sounds pretty bad (not as bad as the reviews claim, once the cheapo speaker breaks in you get decent tones, that and an EQ pedal), and as of now nobody has come out with a mod for it.

I got in touch with an Ebay seller who has one "Modded Crate V5" on sale but he asks 230 bucks for it and doesn't sell any mod kit for it (he claims modding this amp consists on almost building an entire new circuit).

I'm sure i'm not the only one stuck with a V5 waiting for mods... any help?

[Andy]

best way to mod one? sledgehammer.

[Tarin]

Sledgehammer... not a good idea, the cab in itself is alright.

[tunghaichuan]

Have you ever worked on tube amps before? Do you have a DMM? Do you have a schematic for the amp?

I believe the V5 is the same amp as the VC-508, but with different cosmetics.

I've never seen the inside of one, so it may be hard to mod if there are SMDs on the PCB.

tung

[Tarin]

Nop, not a licensed tech or anything... i consider myself a good tinkerer and good with a soldering iron, but i could never come up with the slightest idea on how to mod a tube amp.
That's why i'm waiting for some mod-kit to come up (with instructions), that i can manage. BTW, i'm aware of the dangers involved in tube amps, and know the right proceedures for a proper drain.

Schematics i don't have but i'll start working on getting those (never dealt with Crate people).

As of now, i only have some pics of the amp's board (if that gives any help).

http://i134.photobucket.com/albums/q86/tarinazo/Crate%20V5/DSC03622.jpg

http://i134.photobucket.com/albums/q86/tarinazo/Crate%20V5/DSC03630.jpg

http://i134.photobucket.com/albums/q86/tarinazo/Crate%20V5/DSC03631.jpg

[Tarin]

A few more pic's of the Crate V5...
http://i134.photobucket.com/albums/q86/tarinazo/Crate%20V5/DSC03633.jpg

Sovtek tubes...
http://i134.photobucket.com/albums/q86/tarinazo/Crate%20V5/DSC03626.jpg

And here, the 99 dollar cab and crappy speaker...
http://i134.photobucket.com/albums/q86/tarinazo/Crate%20V5/DSC03624.jpg

[tunghaichuan]

The good news is that it looks like there are no SMDs on the board.

One thing I would check is the bias. If the schematic I have is correct, the cathode bias resistor is only 100 ohms. It seems like it should be bigger.

You will want to check the plate voltage as well.

What are you trying to accomplish by modding your amp?

tung

[Tarin]

The amp lacks of bass tones, and the overdirve is kinda fuzzy. the volume range jumps drastically when dialed between 6-7... cleans are ok.

The tone knob is really wierd... seems to be a -10/0/10 kinda knob where turning it from one end to the other (0 to 10) the tone at 0 seems be down, then go up at the middle (5) then down again when reached 10 (dunno if i explained myself).

I've read a few other reviews were changing the speaker and tubes helped for some, but others claim that not even that helped (i don't have extra speakers nor tubes to try this out).

So basically the mods consist in providing some bass to the amp and making the tone knob work correctly.

[tunghaichuan]

Just to make sure I'm looking at the same schematic, what value do you have for R17? On my schematic, it is a 100 ohm, 5 watt resistor.

The circuit should have plenty of bass. I would guess that it is a combination of the 10" speaker and a small output transformer. I wouldn't know what to recommend for a replacement, it depends on how much real estate is on the chassis, and how the OT is connected into the circuit.

The volume control is kind of weird. On my schematic, it is a 10k linear pot. On most circuits this control is 470k to 1 meg ohms and would be an audio/log pot.

The tone control looks like a modified Baxandall to me, but I could be wrong. It definitely isn't the treble cut tweed type that I'm familiar with.

The input gain stages is a cascaded opamp. A TL072. Any of the replacements will give you slightly differing results. I would pull the stock opamp and put in a socket so you can swap them out easy. I believe the TL072 is pin-compatible with the Tube Screamer types. You might even want to spring for a spendy Burr-Brown type.

tung





The amp lacks of bass tones, and the overdirve is kinda fuzzy. the volume range jumps drastically when dialed between 6-7... cleans are ok.

The tone knob is really wierd... seems to be a -10/0/10 kinda knob where turning it from one end to the other (0 to 10) the tone at 0 seems be down, then go up at the middle (5) then down again when reached 10 (dunno if i explained myself).

I've read a few other reviews were changing the speaker and tubes helped for some, but others claim that not even that helped (i don't have extra speakers nor tubes to try this out).

So basically the mods consist in providing some bass to the amp and making the tone knob work correctly.

[Tarin]

I got in touch with LOUD Technologies and they kindly sent me the schematics, PCB assembly and parts chart promptly. (i can email them if needed).
Tung, i really appreciate your interest on helping out making this little amp something worth the 99 bucks...

R17 is: WR 330 5% 5W

As for the volume pot, it's a 250K 05A 15mm single unit.
Tone pot 250KB 15mm single unit.
R12 reads 43K .25W

http://i134.photobucket.com/albums/q86/tarinazo/V5Schematics.jpg

[sumitomo]

best way to mod one? sledgehammer.

I'm with Andy whip out that 5 lbs. precision adjuster and have at her.Sumi:D

[Tarin]

Tung, i'll post your email comments (for anyone following this thread):

Looking at the schematic, it looks a lot like the VC-508. The V5 isprobably an update of the older amp with a larger speaker and someupgraded parts values. Do you want more bass in the clean sound or distorted sound? You couldbump up C1 to 22uF/50v, but it might make the amp sound flubby/farty. Other areas to look at would be replacing the speaker with a better oneand replacing the output transformer with a better one.

To me, cleans sound ok... i'm using humbuckers so messing with the tone knob on my guitar get's me some good tones on it.
While overdriven the amps sounds ice-picking thin, i use a multieffect pedal, Digitech RP250 and all my distortion based presets sound like that to (not thru my Vox Pathfinder 15R).

The speaker replacement issue is a bit confusing... the only spare speaker i could use is the 8" stock one on my Vox 15R and as a said erlier on this thread, lots of reviews claim that swapping the speakers and tubes helped, and others claimed it didn't... so, i'll try using the smaller speaker i have at hand (not a big step forward, but might help).

As for the OT, same issue... i had to buy one.

At first i thought i could get decent tones just by replacing resistrors and such (an inexpensive and fun way of modding) rather than swapping parts (no fun-labor factor there, and could be a bit expensive)... but i guess that drill goes: first swap stuff then mess with the board.

any recomendations on an inexpensive OT?... theres a lot of space in the cab.

[Tarin]

Now we have one question answered, there's a post on Youtube with a comparison of two V5's: one stock and one with a Celestion G-10 speaker on it.
On a side by side camparison you can tell that a speaker change helps a lot.

Video is posted by The Tone King... great reviews from him.
http://www.youtube.com/watch?v=na0mrc1QZoY

Take a look and tell me (us) what you think now that you can be able to listen to a stock V5.

Oops, +-100 bucks for a G10 speaker... ouch.
Any recomendations on a good not-so-expensive 10" speaker?

[Andy]

I heard a crate with the warehouse spkr greenback clone($69-green beret) in it and it made a world of difference.,,well worth the expense

edit* my bad, that was a 12"

[tunghaichuan]

I heard a crate with the warehouse spkr greenback clone($69-green beret) in it and it made a world of difference.,,well worth the expense

edit* my bad, that was a 12"

Warehouse makes a 10" speaker as well:

http://warehousespeakers.com/products.php?cat=8

Probably better sounding than the stock speaker.

I really hate to recommend this one but for an inexpensive, good sounding OT, Edcor USA makes a decent one. I hate to recommend it because it comes with faston solder tabs. It looks identical to the one here:

http://www.diycustomamps.com/images/18W_lite/chassis_pt2/chassis_57.jpg

These are inherently unsafe as there is exposed B+ outside the chassis, not a good idea. If you decide to use one of these, be very careful and insulate all the solder tabs. Don't touch the OT with the amp on. They're about $20US + shipping.

tung

[deafelectromark]

I bought one of these after I sold my perfectly modified Epiphone Valve Junior with the help of 18watt members and 300+ pages of chit-chat. I get bored rather easy, and was going to go with the Valve Junior again (I sold it to see if I could get the combo and do similar things, but the price increase told me that there were greener pastures) as a platform, but decided to try out the Crate V5 since it was a combo not much bigger than the VJ. I like 10 inch speakers, I liked the looks of the amp, and thought that even if I have to replace everything and even make up a tagboard for it, it would still be cool. I also was hearing what others have been saying about the Crate and when I got it, surprise! I agreed that there was something amiss and decided that to just accept it and give it back would be like throwing in the towel. I knew that it could be better and I systematically worked on each section to see how my $100 initial investment could be improved on.
Speaker was pulled first. Weighing about a pound and with a tiny magnet, tiny voice coil, stiff suspension and a plastic (!?) cone, I could tell just by tapping on it that this was a tone sucker and big part of the bass weakness. I figured that it could be used in an amplifier to take to the beach or other dirty, wet place. The chassis looked awfully close to the speaker magnet, and I didn't think I could get anything in there that would be decent.I measured the depth of other speakers that I had and found that I was wrong. There WAS room for a better speaker. I popped in a 50 watt Eminence 10 inch and it cleared the chassis. Hooked it up and fired it up- better tone and bass, but the amp was still shrill and unmusical.
Looking inside the amp on the circuitboard I saw of all horrors, an op amp!. OK, I know, you can get good sound out of op amps, but looking at the circuit with the volume control in the feedback loop in the second stage, was didn't sit right with me. After the op amp, the tube circuit was fairly conventional other than a quasi- parametric tone circuit between two tube sections of the 12AX7. But looking at the output of the second triode section, I could see that 90% of the signal was dumped just before it got to the grid of the power tube. I guess that is why they needed the op amp in there- to make up for lost gain in the output tube's voltage divider at the grid. (Why?)
So what I did is to cut some traces and add some jumpers to make it an all tube amp. After the input resistors (1.5Kohm and 1 Meg) I cut that trace going to the input of the op amp and sent it straight to the first tube grid and cut away any other parts that were there that might have influence. I decided that the tone control was not a bad thing, just different- and I left it as is. Since I now had a 250Kohm volume pot out of the circuit, I put that between the tone circuits and the grid to the second triode in place of the attenuation scheme that was there and to maintain grid to ground loading and control. I cut the traces around the volume pot and ran jumpers to the appropriate places (the pot connects to the output of the tone circuit, the two lower resistors were cut out, and the other end of the pot was run to ground. The wiper fed the second triode's grid.
I checked for stability (good) output power-6.1 watts at clipping; up to 9 watts fully overdriven. and residual noise 7mV rms (from the power supply). The tone control can be more easily understood when you use a fuzz pedal or other distortion box into the input. It changes the midrange tone in weird ways, but it is better than just a treble cut, since your guitar already has that. Put your metal pedal in front of it and see how much range of tones you can get from it.
Clean on this amp is very good. You can have your amp set at 12 noon, and your guitar all the way up and it will be clean until you start hitting notes hard (or if you have hotter pickups, perhaps a bit sooner. Alternately, you can turn the amp all the way up and still get clean tones with the guitar just cracked open and swell into the realm of output tube distortion. It is very easy on the ears and very pedal friendly. Using external EQ helps you get the tone that you need/want from various axes.
I had ordered a new transformer for this amp (EDCOR 15 watt- the same one I used in my Valve Junior with great success- $20.64 plus $6.37 shipping), but I am happy enough with it the way it is (the output transformer in the Crate is much bigger than the Valve Juniors'- 10 watts instead of 5). I get deep tone from only a 10 inch speaker and I have to be careful not to use the neck pickup too much- it rattles the pictures and things on the wall in the living room. That transformer is going to have to wait for my 6550 single-ended project. One big output tube- should be cool and about 10 watts!
If you just want to add lots of gain easily and just get your feet wet in trying things, pull out resistor R27 (10K) and short out R 15 (100K) and that will get all the lost voltage (the sound) to the output tube and not lost in those 2 resistors. That way you still have the 2-stage op amp pre driver and it might be more of what you want (if more is better- like metal tone). I wanted pure tube and I got it with only an Exacto knife, 3 pieces of short wire, and some cutters and soldering rig, I didn't need to replace the output transformer, or add any parts in any location. Other than replacing the speaker, that was my only expense. I got the 50 watt Eminence for $12.00 each when I bought 4 from a music outlet store on line. I have used those speakers in amps from this 5 watt one to a stereo 15 watt rig and for a 40 watt combo as well. Tubes are all stock. Surely a better transformer and/or tubes will make a difference, but I got night and day difference with these simple mods. Sounds great for little $$$. If you want, and you can pull the board and replace it yourself, I can mod it for anyone for $40.00 plus shipping (which would be nominal in a Priority mail flat rate envelope ($5.00). There is hope for Crate V5 to become the 'next big thing in small amps.

Deafelectromark (alias manoteal):rockon:

[SuperSwede]

Hello Deafelectromark (alias manoteal) and welcome to the fret net.
You seem to like to write a lot, so why dont you write something about yourself in the fret players section?

[deafelectromark]

Hello Deafelectromark (alias manoteal) and welcome to the fret net.
You seem to like to write a lot, so why dont you write something about yourself in the fret players section?

Hi Super,
Yes I am new to the Fret. I have been a member of other sites, most notably 18 watt and now SEwatt. I have been selling on eBay for about 5 years now and I am a deaf musician. You can read my bio on eBay (deafelectromark) and if you tell me where to post a howdy here, I will do so.
I was drawn to this site when a friend in Mexico was having similar concerns with the poor quality sound from the Crate V5- an amp that I bought with the hopes of improving, since many people were also dissatisfied.
I have been doing electronics for over 40 years, got a Electronics technician certificate at trade school, taught eleactronics at that same school for a time, worked in high-end (read $$$$$) audio during the heyday of CD's coming on the scene and home theaters going into the rich folk's homes. They would look at my hearing aids and appear puzzled. Some would just come out and say, "How can you do your job if you can't hear?" I told them that as long as their ears were happy, then I would take their money. If not, tell me what isn't right and I will make it so. After all, it is THEIR ears that are important, right?
Started playing stringed instruments in 1967- first autoharp, then banjo, then piano and guitar and was in the school band playing drums from 4th grade through high school graduation (Concert Band, Marching Band, Orchestra (tympani), etc. Made the guitar my main thing when I was grounded for a Summer my Sophomore year in High School- nothing better to do.
Lost my hearing gradually. didn't wear hearing aids until I was 18. They stopped being useful when I turned 40. Went to college, got a couple of degrees in Deaf education, and now am a registered Drug and Addictions Intern. Worked with only deaf people for a while, got bored of that (try to explain music to a deaf person- you might as well talk about colors to a blind one).
Implanted with cochlear device in 2002- now I have my brain wired so I can plug stuff right into it. Yes, even a guitar. I can hear a fly's fart in a quiet room. I just got the latest model, and it is WAY too sensitive. I don't want to hear ALL that. Volume does not go to zero as programmed. I am getting that fixed in a week or so. Can't complain, when I want quiet I just turn it off.
So Hi Ya'll! Lets let the fun begin! Don't be shy now, jump on in!

Super,
You can cut and paste this intro into the proper section, or guide me to it and I will do it.

[Tarin]

Hello mark, mexican buddy here.
Just read your bio and can't manage to clos my jaw... that must be the shortest/best explained/interesting and surprising bio i've read in a long time (people at Myspace could learn how to get a message thru).

[Bloozcat]

Yep, i'm one of those who fell for the Crate V-Series blowout sale, at first i bought the V-18, and considered it a good amp, great for the price... sold it after a great offer made to me.
Went back to MF only to find out they were out of stock (also in GC, Sameday, Samash and everywhere).
Made my homework on the V5, and althought it had bad reviews i went for it thinking "how bad could it be" and "even if it's that bad, somebody will come out with mods for it".

Well, the amp sounds pretty bad (not as bad as the reviews claim, once the cheapo speaker breaks in you get decent tones, that and an EQ pedal), and as of now nobody has come out with a mod for it.

I got in touch with an Ebay seller who has one "Modded Crate V5" on sale but he asks 230 bucks for it and doesn't sell any mod kit for it (he claims modding this amp consists on almost building an entire new circuit).

I'm sure i'm not the only one stuck with a V5 waiting for mods... any help?

Try going over to www.sewatt.com and sign up. There's a new Crate 5 watt discussion just starting there. There's not much info yet, but it may generate some. There's not a whole lot of love there for the Crate 5 watt circuit, so be forewarned. It might need darn near a whole new circuit...:)

EDIT TO ADD: I see our new member deafelectro has already been in the Crate discussion on sewatt.co as his alter ego Manoteal...I thought his post here looked familiar...:D

[Tarin]

Now back to the main concern: upgrading the V5.

Deafelectro... That's some great task you've acomplished in the little amp. i might catch you up on sending the board to get modded and be the first one to review and experiment with your findings.
I already got your email so i'll get in touch with you next week to make this happen.
Now for the speaker issue... is there any way of including one of your leftover Eminence's in the picture?

[deafelectromark]

Hello mark, mexican buddy here.
Just read your bio and can't manage to clos my jaw... that must be the shortest/best explained/interesting and surprising bio i've read in a long time (people at Myspace could learn how to get a message thru).

Thanks C.
Your last line is cryptic- what do you mean concerning Myspace? That they can't speak succinctly? It is a skill after all. I do become quite long winded (see first post above), but last night you (and the rest of us) got lucky. I was passing out from lack of sleep. I just HAD to say what I said. That said- let the music begin!
M:beer:

[jim p]

I bought a V5 from Musicians Friend for 80 bucks and have started modifying it. I have two Epi valve Jr. Amps one that I added reverb, triode pentode switch, and Alnico Weber speaker to and the other with FET input high voltage regulator and 6V6 installed. I saw the schematics for the V5 on the web and can see right away they have an amplifier with a solid state preamp (TL072) and tube output not what most people want but easy to fix. Getting the amp found the stock speaker is probably not a guitar speaker so first thing was playing it through the valve Jr speakers also a pair of Jensen 10 special designs made a big difference. So ordered a new speaker from Ted Webber (they have 15% off right now so 43 bucks total with shipping) they make the stock speaker in the old valve Jr. I think. For circuit mods so far I did not remove the Op Amp because it is used for high frequency bypass (above 100Hz) and pre emphasis (boost the highs so the tone control can take them out or pass them through). So I removed R13 to change IC1-A to unity gain and use as a high impedance buffer to not load down the guitar pickups. Next removed C26 changed C24 to 47nF (Note this should be 100nF) removed C27 and installed a 33k resistor in its place removed the 250k pot to use as a volume control after the tone stack. Lifted the 100nf C25 at the node connecting it to R2 and R1 putting a 33k resistor with a 10 nF cap accost it in series (this is now the pre emphasis for the tone stack) With these changes if you over drive the amplifier input with overdrive instead of the OP Amp clipping (awful noise) the first stage tube will clip (as man and god intended when tube amps were created) Next on the tone control changed C6 to 25 nF removed C5 (not sure where a frequency this high is going to come from) and removed C4 (so when you turn the tone control all the way up it does not go to no highs) Now to install the volume pot removed R15 and R27 connected the 250K pot CW1 that was in the Op Amp feedback to ground on the wiper full CCW side connected the wiper to junction of R15, R27, R7 and the grid of J2-A and the third terminal of the pot to junction of R29 C28. Now the tone is set to flat at a quarter turn (9 o’clock position). Then checked the output of the amplifier with a frequency generator and scope and found that it did not clip equally at high volume and started to oscillate. Fixed that by lowering the cathode bias resistor to what the data sheets call out for 270 ohms. Also changed R22 the resistor in series with the power indicator to 150 ohms but it is still to bright will probably go to 220 ohms also it is a light bulb not an LED.
As always if you do mods to a tube amplifier be careful of the high voltages in this case a plate voltage of 316 volts. There is a bleeder resistor R24 so that helps but use a volt meter. And always remember the one hand rule do all your probing with one hand make sure no other part of your body or your other hand is tied to ground.
I changed the value of C24 above found lowest frequency from guitar to be 82Hz not 190Hz.

[Tarin]

Wow, that's some major modding. Unlike what Deafelectro achieved with his more simple mods.
I've been in touch with Deafelectro for him modding my V5 since he's is the only mod i've come up in the internet.
But now that you have accomplish another one...it's only fair to take in consideration, any clips? pics?

[jim p]

I have no pictures or sound clips right now. Would like to post a marked up schematic if I get a chance maybe pics. It sounds like a lot of mods but it’s not really but maybe that is because I am an electronic engineer in analog design. I did all the mods with no cuts to the PC board I did have to attach wires to the volume pot to connect it the pc board and add electrical tape under it to prevent a short to the board. All the other mods except the pre emphasis mod (33k ohm with 10nF in parallel between C25 and R1, R2) are removing components and leaving them out, changing there value or in the case of C27 replacing it with a resistor. At the least I would change R17 to 180 ohms to stop the oscillation in the EL84 output tube I just paralleled it with another 330 ohm 2 watt (165 ohms) as a quick modification. With the Op Amp input I just wanted to use it as a buffer circuit with minimum gain (equal to loss in pre emphasis circuit) so if you overdrive you will clip the first stage tube. I was hoping that I could fit a set of dual concentric pots in place of the two pots so I would have gain, tone, volume and reverb controls on the front panel. I am going to add reverb using a Ruby tank from a Crate V33 head that I changed to an Accutronics 3 spring tank. Will probably change the output tube to a 6V6 this is for my son as a practice amplifier he likes Fender amps with reverb. Good chance will need a triode/pentode switch also. I have modified the Crate V33 head and a Crate V50 and have a V18 (will change to 6V6 output class AB) on order like fooling with tubes and these are so cheep for what you get. You have to remember it is hard to kill a tube (as long as it is cathode biased) unlike transistors, fets and ICs. If you do something wrong will probably just get no sound out.

[jim p]

I have attached pictures of mods and sections of schematic where changes were made. I may do a step by step explanation of the modifications in the future.
Error value of C24 should be 100nF not 47nF found lowest frequency from guitar is 82Hz not 190Hz.

[Tele-Dave]

http://i134.photobucket.com/albums/q86/tarinazo/V5Schematics.jpg

Can you please post this at a higher resolution, or maybe link as a pdf. When
trying to magnify, all it does is blur.

Thanx,--- Dave

[Tarin]

Crate V5 schematics

[Tarin]

Jim_P... thanks a lot, i'll take a look at what you've done and maybe i'll do thos mods to mine, although a step by step will help a lot.

I'm pretty sure that this thread is gonna recieve lots a visits cause i know theres a lot of people waiting for a DIY mod for this little amp.

I have some pics of what Deafelectro did to his and it's different from what you did... i would like to post them but, i'll need deafelectro's permission for that.

[Tele-Dave]

Crate V5 schematics

Thnx for schem.........Dave:bravo: :beer:

[Tele-Dave]

Would like to post a marked up schematic...............


Please Do. looks like a good mod.

[jim p]

Step by step modifications done to Crate V5 amp

1) Remove the amplifier from cabinet. First remove speaker jack then the six screws holding back cover of amplifier then with amplifier upside down remove four screws two on each side of cabinet that hold amplifier chassis in cabinet. (Note: you may want to enlarge the holes slightly in sides of cabinet and on back cover to make reinstallation and future removal easier)

2) If you haven’t already done so (you do have this unplugged right?) get out a dc voltmeter the highest voltage in the amplifier is approx. 320 volts DC measure from chassis to R25 should be 0 to 15 volts if so you are safe. This amplifier has a bleeder resistor R25 so supplies should drop after power down.


3) Remove preamp (12AX7) and power tube (EL84 6BQ5) put them some where you wont break them.

4) Next remove knobs on front panel may require flat blade screwdriver and a thin piece of wood to work against to prevent scratching front panel. The pots are D shaft type walk then off gently. Then remove nuts holding pots and ¼ inch jack on front panel.


5) Now make note of all the connections to the PC board because you are going to remove them. If you have a digital camera now is a good time to use it. Also if you print out the schematic note wire color and location on it. The faston connectors J4 J5 J1 and J2 may be hard to remove don’t break them of pcb by working them back and fourth.

6) Next remove the six screws that hold PCB into chassis and take it out. (hope you are putting parts someplace you wont loose them)

PC Board modifications
(See attached pictures of mods and changes to schematic also pic DSCF0947.jpg in previous post is the pre emphasis mod the tone mod is incorrect in that post tie unused side of pot in tone control to wiper not ground or unconnected up to you)

1) You are going to be removing approx 10 parts. You will need solder, solder wick, soldering iron, needle nose pliers and desoldering tool. In manufacture the compnet leads have been bent so desolder a componet lead then straighten it before removing or you may damage PCB plated feedthrough.

2) This modification will use the two Op Amp stages for an input buffer and small gain to over come loss due to pre emphasis circuit that will be added. Desolder and remove volume pot from PCB. Next remove R13 this makes IC1-A a unity gain buffer. Remove C26, C24 and C27 replace C24 with a 47nF 50-100 volt poly cap.C24 sets the low frequency limit at input to the amplifier with 47nF this is approx 125 HZ 3db down (for more bass use 100nF). In the place of C27 install a 33k ¼ watt resistor this equals a gain of 1.22 for IC1-B (want to keep gain low so first stage tube will clip before the Op Amp with overdrive).
ERROR Value of C24 should be 100nF lowest frequency from guitar is 82Hz.


3) Pre emphasis circuit For the tone control to be able to cut, boost and be set for flat response the high frequencies need to be boosted first. So C25 needs to be removed if you want replaced or use it again for this mod. Install one lead of a 100nF 50-100 volt cap into plated hole (via) that is connected to pin 7 of IC1 in the second hole of C25 insert lead of 33k ohm ¼ watt resistor with a 10nf capacitor accost it then connect the other lead of the 33k resistor to the second lead of the 100nF capacitor. If you want full treble brighter you can lower value of R2

4) Tone stack and volume control Here we will put volume control after tone stack and first tube stage so you will be able to overdrive input tube and still control volume. Remove C5 C6 C28 and C4 Change C6 to a 22nF 50-100volt poly capacitor. (Here a lower value cap will raise where the tone control will cut the highs higher value will lower it.) Now the volume control remove R15 and R27 using the volume pot removed from the board you will need to bend the leads 90 degrees towards the back of the pot to attach 1 ½ inch wires to the three terminals of the pot. Also need to insulate PCB were pot was attached to prevent shorting (three layers of electrical tape works) looking at the front of the pot as use to be connected to the PCB the right side terminal connects to the plated hole C28 that connects to R29 the center terminal (wiper) connects to the plated hole of R27 that connects to R7 and control grid (pin 2) of the 12AX7. The last terminal goes to the plated hole of R27 that goes to ground. (note be careful the leads soldered to pot do not short to metal back shell of pot no sound out of amp)

5) Oscillating power tube in testing the amplifier found output did not clip symmetrically and oscillated when clipped. Based on the tube data sheets the cathode biasing is to high in value. Change R17 to 270-300 ohms 2-5 watt or parallel the 330 5 watt with another 1.5k ohm 2 watt (270 ohms)


6) That’s it now put it back together and be careful around high voltage always follow one hand rule working on tube amplifiers. The one hand rule is make sure other hand and body are not tied to ground other hand does all the probing. So tie meter or scope ground to the chassis ground then do all your measurements.

Other tweaks
From the way this amplifier is set up it may have had gain, tone and volume controls?
And they took the volume control out instead of the gain control so if you add a third 250k pot across TL01-B same as in the stock schematic this will be a gain control you should add a 27k resistor in series to set minimum gain at unity (1).

Lowest frequency amplified the stock value of C24 is to low 3db down at approx 270Hz the value in the mod is 47nF for 125Hz if you want you can go bigger 100nF but this may increase that annoying 60 Hz hum we have all come to love.
ERROR Should go with 100nF lowest frequency from guitar is 82Hz

On the pre emphasis mod you can change the value of R2 to increase or decrease the brightness of the maximum tone. Higher value for R2 (stock 100k) will reduce the maximum lower value increase it. If you lower the value you may want to increase the gain in the Op Amp stage to offset the loss.

Tone control pot from my results the tone is flat at the 9 o’clock position so if you use a 100k (125K) pot for the tone control this will move it to the 12 o’clock position.
Changing where the tone control operates you can reduce the value of C6 to raise or lower where the tone control operates but you should change the value of the cap in the pre emphasis circuit also (10nF across 33k ohm).

[tunghaichuan]

Cool, thanks for posting that. The Best Buy near me has these for $100, I may have to pick one up and try the mods.

Have you tried adding additional capacitance to kill some of the 60hz hum?

tung



Step by step modifications done to Crate V5 amp

1) Remove the amplifier from cabinet. First remove speaker jack then the six screws holding back cover of amplifier then with amplifier upside down remove four screws two on each side of cabinet that hold amplifier chassis in cabinet. (Note: you may want to enlarge the holes slightly in sides of cabinet and on back cover to make reinstallation and future removal easier)

2) If you haven’t already done so (you do have this unplugged right?) get out a dc voltmeter the highest voltage in the amplifier is approx. 320 volts DC measure from chassis to R25 should be 0 to 15 volts if so you are safe. This amplifier has a bleeder resistor R25 so supplies should drop after power down.


3) Remove preamp (12AX7) and power tube (EL84 6BQ5) put them some where you wont break them.

4) Next remove knobs on front panel may require flat blade screwdriver and a thin piece of wood to work against to prevent scratching front panel. The pots are D shaft type walk then off gently. Then remove nuts holding pots and ¼ inch jack on front panel.


5) Now make note of all the connections to the PC board because you are going to remove them. If you have a digital camera now is a good time to use it. Also if you print out the schematic note wire color and location on it. The faston connectors J4 J5 J1 and J2 may be hard to remove don’t break them of pcb by working them back and fourth.

6) Next remove the six screws that hold PCB into chassis and take it out. (hope you are putting parts someplace you wont loose them)

PC Board modifications
(See attached pictures of mods and changes to schematic also pic DSCF0947.jpg in previous post is the pre emphasis mod the tone mod is incorrect in that post tie unused side of pot in tone control to wiper not ground or unconnected up to you)

1) You are going to be removing approx 10 parts. You will need solder, solder wick, soldering iron, needle nose pliers and desoldering tool. In manufacture the compnet leads have been bent so desolder a componet lead then straighten it before removing or you may damage PCB plated feedthrough.

2) This modification will use the two Op Amp stages for an input buffer and small gain to over come loss due to pre emphasis circuit that will be added. Desolder and remove volume pot from PCB. Next remove R13 this makes IC1-A a unity gain buffer. Remove C26, C24 and C27 replace C24 with a 47nF 50-100 volt poly cap.C24 sets the low frequency limit at input to the amplifier with 47nF this is approx 125 HZ 3db down (for more bass use 100nF). In the place of C27 install a 33k ¼ watt resistor this equals a gain of 1.22 for IC1-B (want to keep gain low so first stage tube will clip before the Op Amp with overdrive).


3) Pre emphasis circuit For the tone control to be able to cut, boost and be set for flat response the high frequencies need to be boosted first. So C25 needs to be removed if you want replaced or use it again for this mod. Install one lead of a 100nF 50-100 volt cap into plated hole (via) that is connected to pin 7 of IC1 in the second hole of C25 insert lead of 33k ohm ¼ watt resistor with a 10nf capacitor accost it then connect the other lead of the 33k resistor to the second lead of the 100nF capacitor. If you want full treble brighter you can lower value of R2

4) Tone stack and volume control Here we will put volume control after tone stack and first tube stage so you will be able to overdrive input tube and still control volume. Remove C5 C6 C28 and C4 Change C6 to a 22nF 50-100volt poly capacitor. (Here a lower value cap will raise where the tone control will cut the highs higher value will lower it.) Now the volume control remove R15 and R27 using the volume pot removed from the board you will need to bend the leads 90 degrees towards the back of the pot to attach 1 ½ inch wires to the three terminals of the pot. Also need to insulate PCB were pot was attached to prevent shorting (three layers of electrical tape works) looking at the front of the pot as use to be connected to the PCB the right side terminal connects to the plated hole C28 that connects to R29 the center terminal (wiper) connects to the plated hole of R27 that connects to R7 and control grid (pin 2) of the 12AX7. The last terminal goes to the plated hole of R27 that goes to ground. (note be careful the leads soldered to pot do not short to metal back shell of pot no sound out of amp)

5) Oscillating power tube in testing the amplifier found output did not clip symmetrically and oscillated when clipped. Based on the tube data sheets the cathode biasing is to high in value. Change R17 to 180 ohms 2-5 watt or parallel the 330 5 watt with another 330 ohm 2 watt (165 ohms)


6) That’s it now put it back together and be careful around high voltage always follow one hand rule working on tube amplifiers. The one hand rule is make sure other hand and body are not tied to ground other hand does all the probing. So tie meter or scope ground to the chassis ground then do all your measurements.

Other tweaks
From the way this amplifier is set up it may have had gain, tone and volume controls?
And they took the volume control out instead of the gain control so if you add a third 250k pot across TL01-B same as in the stock schematic this will be a gain control you should add a 27k resistor in series to set minimum gain at unity (1).

Lowest frequency amplified the stock value of C24 is to low 3db down at approx 270Hz the value in the mod is 47nF for 125Hz if you want you can go bigger 100nF but this may increase that annoying 60 Hz hum we have all come to love.

On the pre emphasis mod you can change the value of R2 to increase or decrease the brightness of the maximum tone. Higher value for R2 (stock 100k) will reduce the maximum lower value increase it. If you lower the value you may want to increase the gain in the Op Amp stage to offset the loss.

Tone control pot from my results the tone is flat at the 9 o’clock position so if you use a 100k (125K) pot for the tone control this will move it to the 12 o’clock position.
Changing where the tone control operates you can reduce the value of C6 to raise or lower where the tone control operates but you should change the value of the cap in the pre emphasis circuit also (10nF across 33k ohm).

[jim p]

When I was talking about 60 Hz hum I meant pick up from the guitar not in the amplifier. The amplifier has 1 H choke pi filter and DC filament voltage on the 12AX7 its quiet compared to the Valve Jr combo I have.

[jim p]

Posted pictures of close to final modification of Crate V5 I bought. The vector board is the reverb drive and recovery amplifiers. Replaced the stock (crap) speaker with a Webber ceramic 10S for 38 bucks with shipping. The reverb tank is a Accutronics box with Ruby OEM guts (2 spring) from a Crate V33H. On the back pannel is the reverb pot and pentode/triode switch. May do a better job of running the RCA lines to reverb in future. I see the Crate V5 is 85 bucks at Best Buy dot com with in store pick up so the shipping is free.

[Tele-Dave]

Posted pictures of close to final modification of Crate V5 I bought. The vector board is the reverb drive and recovery amplifiers. Replaced the stock (crap) speaker with a Webber ceramic 10S for 38 bucks with shipping. The reverb tank is a Accutronics box with Ruby OEM guts (2 spring) from a Crate V33H. On the back pannel is the reverb pot and pentode/triode switch. May do a better job of running the RCA lines to reverb in future. I see the Crate V5 is 85 bucks at Best Buy dot com with in store pick up so the shipping is free.

Can you post schematic changes and step by step for these mods?

Question on previous mods. In step 2 of board mods where you remove C26 C24 and C27, C24 and C27 are replaced with other components but C26 is not. Is this left open or is it jumpered? If not jumpered then I assume it is O.K. to remove R28 since it is not connected to anything?

Also I want to have Gain and Volume setup. Can I just leave existing pot connected in its place on board and use another pot for the volume mod such as you have it? I understand that I will have to lift a leg on pot or cut trace on board to put in 27k resistor in series with pot. Is this right?

Thnx---Dave

[jim p]

Yes if you want you can remove R28 without C26 it has no function. If you want gain and volume CW1 the 250k pot accost TL01-B can be used as a gain pot. In that case do not install a resistor in the location of C27. You may to set a minimum gain by putting a 10k resistor in series with the 250k gain pot. If you search the web or call Crate for a VC508 schematic this will give you an idea of the gain, tone and volume set-up. I don't like the values of capacitance they used for the 508 also the low supply rails on the op-amp (+7 -7). This amp is better in the fact you have +/- 15 volts (more within limits if you reduce R19 and R20) for the op-amp a 1 Hennery choke in the plate supply and DC filament supply on the 12AX7. Bad thing is they took out the wrong pot to remove the gain function did not change bandwidth for a 10 inch speaker (more bass) and used a crappy speaker.

[Tele-Dave]

Yes if you want you can remove R28 without C26 it has no function. If you want gain and volume CW1 the 250k pot accost TL01-B can be used as a gain pot. In that case do not install a resistor in the location of C27. You may to set a minimum gain by putting a 10k resistor in series with the 250k gain pot. If you search the web or call Crate for a VC508 schematic this will give you an idea of the gain, tone and volume set-up. I don't like the values of capacitance they used for the 508 also the low supply rails on the op-amp (+7 -7). This amp is better in the fact you have +/- 15 volts (more within limits if you reduce R19 and R20) for the op-amp a 1 Hennery choke in the plate supply and DC filament supply on the 12AX7. Bad thing is they took out the wrong pot to remove the gain function did not change bandwidth for a 10 inch speaker (more bass) and used a crappy speaker.

So no resistor in place of C27. Do I remove C27 or leave it in place?

Also in step 5 you change R17 to 270ohm 5W, but in tung's post next looks like it was changed to 180ohm 5W. Which one is correct?


Thnx----Dave

[Tele-Dave]

Jim, please excuse all of my questions, I'm quite new at this. Want to do the mods, but I want to understand everything that is being done so I will learn something, instead of just replacing things like a robot.
Thnx again,-----Dave

[jim p]

If you keep the volume pot as a gain pot you can leave C27 installed, it will just limit the maximum frequency the op amp will amplify at full gain to 13 kHz. Also may prevent possible oscillation of the op amp.

[Tele-Dave]

If you keep the volume pot as a gain pot you can leave C27 installed, it will just limit the maximum frequency the op amp will amplify at full gain to 13 kHz. Also may prevent possible oscillation of the op amp.

Thnx, Thats just what I was wondering.

So, if I just leave the existing pot in place, leave C27 in place, And not put the 10k in series with the pot, I can get max gain with good breakup because I'm not limiting gain on second stage of op amp. Without the 10k in series would probably be too much and go into clipping, but all I have to do is not crank gain up so much so as to control it, correct. I just want to limit amount of changes if necessary

What would the effect be if I just leave C26 and R28 in place also? Too much bass injection, Treble limiting into second stage of op amp?

Thnx again

[jim p]

Let me explain how the gain of an op amp works for an inverting amplifier. The 2nd stage op amp TL074-B is an inverting amplifier with the gain equal to the feedback resistor (CW1 the 250k pot) divided by the input resistor R14. So with the pot set at 250k the gain is equal to 250k divided by 27k equal to -9.3 if you figure that a strummed cord is 1 V rms (2.8 V p to p) the output will be 26 V p to p just within the supply rails of the op amp ( +15/-15). The minimum gain if you do not put a resistor in series with the 250k pot is 0/27k ohms or zero that is why I recommended to put say 10k ohms (27k would give you unity -1) in series with the pot so you wont have to guess where to set the gain pot if you don’t want to use it. Where are going to put the volume pot on the chassis with this mod?

Regarding the value of R17 I retested the amplifier after adding the reverb looking at the cathode current vs voltage across the EL84 found the cathode current to high giving 14 watts on the plate of the tube so I backed off that value and wound up with a slight tweak to the stock value. It looks that the stock value is not so bad. What I do have now is a 150 pf cap in parallel with R7 (I might try to lower this value to 100-50pf) the reverb required this to prevent feedback and this may have cured the oscillation problem I saw before.

[Tele-Dave]

Jim, I'm going to set up the volume pot just like you have shown it on the schematic. Will mount pot on other side of power switch towards edge of panel. Am going to use shielded wire since it's a long run.

O.K., understand about the op-amp now. (Just learned something-Thnx) Will place a 10k in series with pot.

Will leave value of R17 alone for now.

Am very interested in the Pentode/Triode switch setup

Going to order parts from Mouser tonight for the mods.

Went out today and bought another V5 at Guitar Center to use as a "Control" so I can see how much of a difference this makes. GC had them on sale for $85, plus I had a 10% off coupon, so I got it for $77. Very good price!!

Thnx-----Dave

[jim p]

Looking at the front panel I would consider putting the volume pot where the power indicator lamp is. Then put the power indicator above the power switch. You might be able to get a Knob from Crate tell them one of yours is broken or buy it from them. I don't think shielded cable is necessary for the volume pot you can just twist the ground wire around the other two wires this should be sufficient.
I bought another amp from MF told them Best Buy had them for 85 with in store pick up so they matched the price and shipped for free I saved the sales tax.
You can see the pentode/triode switch in the last pictures I posted on the back panel and inside the cabinet in the picture that shows the reverb vector board.

[Tele-Dave]

Looking at the front panel I would consider putting the volume pot where the power indicator lamp is. Then put the power indicator above the power switch. You might be able to get a Knob from Crate tell them one of yours is broken or buy it from them. I don't think shielded cable is necessary for the volume pot you can just twist the ground wire around the other two wires this should be sufficient.
I bought another amp from MF told them Best Buy had them for 85 with in store pick up so they matched the price and shipped for free I saved the sales tax.
You can see the pentode/triode switch in the last pictures I posted on the back panel and inside the cabinet in the picture that shows the reverb vector board.

Great suggstion on pot and light locations. Wasn't thinking about chassis in cabinet. See there is no room for pot with chassis bolted into cab. Glad you caught me on this. Would of drilled holes and then knob would of interfered with cab.--------Thnx

Will call Loud Tech today and see about knobbbbbbs.

Cant distinguish hookup locations for Pent/Tri switch on pic. Cant see wiring too good. Looks like you lifted leg on R18 and wired DPST switch between R18 and Pin 7 on power tube Can you do a simple drawing/diagram showing install points for hookup and switch wiring for Pent/Tri?

Also what is in R23. My board has nothing in it there. Is that a different value used for Pent/Tri setup???? Dont know too much about Pent/Tri Differences. Will google for info so I will understand it better than only that it changes power output of tube.

Jim, you don't know how much I appreciate all your help here. Thnx much!!


----------------Dave

[Tele-Dave]

Just got off of phone with Loud Tech (Crate)

Pots are $1.50 (Volume--- Part designator CW-1)
Knobs are $1.50

Surprisingly they had them in stock!

Ordered 2 of each so will have extra incase I want to mod other V5 I have.

[jim p]

For the pentode/triode switch I lifted R18 where it connects to the HV supply (J4) and hooked this side of the resistor to the wiper of the switch. Connected one contact of the switch to HV supply (plated hole resistor was connected to) this is the pentode connection. The other contact to the plate of the EL84 pin7 for the triode connection. I still want to check operating current and voltages of the tube in triode mode to see that maximum ratings are not exceeded, forgot to do that the last time I had amp opened up. Along with the drop in output power to approx 1/3 that of pentode mode the brightness of the amp also drops. You would need to lower the impedance of the stage driving the EL84 to over come the Miller capacitance to not have this drop in brightness I am going to go as is for now but in future may try a JFET or op amp between the 12AX7 and the EL84. A pentode has little to no Miller effect cannot get a good number on what the capacitance from plate to control grid is on an EL84 as a triode.

With the miller effect in mind you may want to limit the high frequency range of the first stage tube that you will be over driving with the op amp so I suggest putting a 20 to 33pf cap (300 volts minimum rating) from the plate (pin 6) to the grid (pin 7) of the 12AX7 to roll the high frequency off.

That is as great price for the knobs and pots from Crate did they charge shipping?

I called them for the schematic for the VC508 and the V5 is a variation on the 508 but as I said before done the wrong way and with bad values for a 10 inch speaker.

Oh I forgot that other resistor that you see installed, the board has a location for a resistor in parallel with the 1 H choke I installed a 1k ohm resistor there so a transit would not cause a slight oscillation also if the choke opened it is a little safer.

[Tele-Dave]

When in triode mode, how dark does it get? It isnt too bad, is it? Darker than amp was before tone mods? It is liveable, isn't it?
Going to do Pent/Tri mod anyway. When you come up with a fix, let me know.

Have to dig thru parts box for cap for Plate/Grid. Will try it if I can find one.
Poly cap? Correct?


Was better price for pots and knobs than I thought it would be. Shipping $6

Forgot to ask for schem for 508. Will call them back in few minutes.

As per R23, circuit looks like 1/2 watt or larger would be o.k., Correct?

Question, I want to put a standby switch in also. Would it be that all I would have to do is to install switch to break power at J1 and J2? Correct?


Thanx Jim----------------Dave

[jim p]

Because of the 1 H choke in the power supply you cannot just put a switch in the HV power supply and expect it to last. In a mechanical analogy a choke is like a flywheel it wants to maintain a constant rate it resists change at start up (building magnetic field) and if interrupted (clasping magnetic field). A choke is what is used to generate a spark on a spark plug in a gas engine. If you put the switch at pin 2 J6 (C15 side) when you open the switch the voltage on the choke will go positive to the point of arcing across the contacts in the switch and at some point the switch will fail. If you put the switch on the other side of L1 (J1 pin1) when you open the switch the voltage on the inductor will go negative but this side will work if you put a reverse biased rectifier diode to ground that can handle a minimum of 150mA and reverse voltage of 400 volts (1N4007 should work). Better is to put diode with a low value resistor in series (50 ohms 1 w) in parallel with the choke (cathode on pin 1 side) it will be forward biased when the choke goes negative with the switch opening. Also consider a bleeder resistor on the C15 side for safety.
Me I don’t believe in standby switches so much I don’t think cathode striping happens at these voltages and currents plus the amp is quiet.
If R23 is the one in parallel with the choke on the PCB 1 to 2 k 1 watt is fine.
For the plate to grid cap minimum 300 volt rating mica or poly is fine.

[Tele-Dave]

[QUOTE=jim p]If you put the switch at pin 2 J6 (C15 side) ------If you put the switch on the other side of L1 (J1 pin1) when you open the switch the voltage on the inductor will go negative
QUOTE]

Was talking about putting switch in leads from power trans to where it connects to J1 and J2 on edge of PCB. Just inserting a DPDT to break legs going to PCB and that way I will also have power to supply Indicator light when in standby. Just going to drop out 240V going to Plates
Shouldn't that be just like turning off main power switch as far as choke is concerned?
Was going to interupt both legs of power prior to going to PCB. Connectors are marked J1 and J2 on PCB, and on schematic it is prior to diode bridge and C14/R24 filter and with R24 at ground, should prevent problems that you describe with choke. Is that right or am I missing something????

[jim p]

Putting the switch on the AC side should be ok and avoids dealing with the choke.

[Tele-Dave]

Putting the switch on the AC side should be ok and avoids dealing with the choke.

That was my concern, and why I thought of puting it there. On some other amp schematics I was checking for switch placement, most of them placed switch on transformer secondary leads prior to any other electronics and if there was a choke farther downstream, and i noticed on some schematics that did not have chokes that they put the switch anywhere downstream prior to feeding plates.
Know about collapsing field in coils, that is why didnt want to break either side of coil, and thought that with R24 biased to ground, would bleed off pulse when field collapses. Should be just like turning off main power switch as far as coil is concerned, or that is what I thought.

Thnx Jim, just wanted to verify. Don't know too much about electronics, but was trained in automotive mechanics when there was Points, Plugs and condensers, (and coils) And understand about a collapsing field in a coil of wire producing high voltage surge.

Called Loud Tech again today 3 times, but message says "Our personel are in Training presently, please call back later." I will keep trying to get thru, would like to have copy of schem just so I can compare to V5.

[jim p]

Cathode bias with triode mode needs a higher value of cathode bias resistor vs. the pentode mode. On the amplifier I have modified have found that the stock value of 330 ohms is fine for either modes this results in a cathode current of 38mA in either pentode or triode mode. The result is a maximum plate dissipation of 11.3 watts in the triode mode 10.3 watts in pentode mode.
Driving the EL84 with a signal generator have calculated the capacitance from plate to control grid to be approx 2.2pf in triode mode with the Miller effect this becomes approx 30pf this in parallel with the 220pf has a slight effect on the high frequency roll off of the EL84 (20KHz in pentode mode 19KHz in triode mode) Some of the major changes between the two modes is output power 5 watts pentode mode and 1.5 watts in triode mode. Also plate impedance 38k ohms approx for the pentode mode 2k ohms in the triode mode the result the amplifier is more dampened in the triode mode closer to a solid state amplifier sound then in the pentode mode.

[Tomko]

Ok I now have a tube amp with a new/better speaker. This thing sounds great distorted but I can't get any clean headroom out of it. Can anyone help me? The op-amp circuit is gone. The tone circuit is gone replaced with a Marshall 18 watt tone circuit. The input resistor was changed from 1.5K to 47K. The resistor into the input of the power section was changed from 4.7K to 47K. I'm using a 12AY7 instead of a 12AX7. Still no clean headroom. I think all the distortion is power amp distortion. Can anyone give me some voltages to look for at the pins of the EL84? The bias is stock on the EL84 and I changed it to a Tesla tube. Any ideas?

[letter109]

My first post here folks. . .just wnted to say thanks to Tarin for the hi-res schematic of the V5. I tried calling the Loud Technology toll-free number but they're still out on training or something. . .been that way for several weeks now, eh? Anyway, I got the schem from this group and is greatly appreciated. I have three of those little V5s sitting around here, and I actually like 'em OK out of the box. But I also agree with deafelectro that this may be one of the next big things in little amps, and a great beginning place for a heck of a mod. So, if I have success with anything (or even failure) I'll try to let you all know how it came out. Thanks for a great group. I'm glad to be a member of it. -M

[jim p]

The most important voltage on the EL84 would be the cathode voltage to calculate the cathode current. With the 330 ohm resistor this should be approx 14 volts max equal to 42mA. Ballpark you would then have 38mA plate current and 4mA screen grid current. Not sure the 12AY7 may be problem free by the data sheets it is calling for a higher plate current (3mA) and a lower value grid resistor 100k ohms (may have high grid leakage current vs. 12AX7). I also noted on one data sheet a higher heater current so check to see that you have 12.6 volts across the heater. What are the cathode, grid and plate voltages for both locations of this triode? Have you tried the Sovetek tubes that were stock in the amplifier?

[jim p]

Looking further into the data sheets for the 12AX7 and the 12AY7 based on the plate impedance and the plate current vs. plate voltage you need to change the cathode bias resistors when using a 12AY7. The 12AY7 requires 4 to 3 volts at the cathode relative to ground so a resistor value of 2500 to 3300 ohms should be used for both R3 and R8. With R3 and R8 changed you should have approx 3.5 volts at the cathode and with no signal a DC voltage of approx 170 volts at the plate of each triode (pin 6 and pin 1) hope this helps.

[jim p]

My second V5 modification is changing from EL84 to 6V6GT for the output tube. So far with the exception of taking out the 9 pin socket and replacing it with an octal socket the only change is value of cathode resistor R17 to 380 ohms. I am looking into the value of the screen resistor R18 and may increase it to 5 to 10 k ohms. If someone was into a total rebuild with a 6V6 instead of an EL84 you gain 300mA of heater current capability so you could have two 12AX7 tubes and a 6V6GT output tube within the limits of the power transformer. With that you could have input stage, cathode follower driven tone stack, gain stage, volume stage and output tube. Now will start on adding reverb to this amp and maybe a Weber AlNiCo 10S speaker if it will fit.

[Tomko]

Jim P
Thanks for the good suggestions. I will give them a try. Unfortunately, both the vol. and tone pots have failed mechanically- be careful with them. I can't get in touch with Loud Tech. Anyone know where else I can get them? So the amp is down until I get some new pots. I don't think I tried the stock Sovteks after the mod but I believe I tried a different 12AX7. I had the same results- no headroom. I tried a 12AY7 to lower the gain to get more headroom. Maybe it's the Tesla EL84. So I will proceed with the stock Sovteks after I get some new pots. Thanks again.

[rock_mumbles]

Hi Tomko, as far as your lack of clean headroom.

What mods have you done, you said you took out the op amp circuit, changed the 1.5K to a 47K and the 4.7K on the EL84 to a 47K, is that all you have done?
Did you leave R11 (1M) resistor to ground after the input resistor and remove R2 (100K)?
What I did to clean up one of my Valve Juniors was to decrease the value of the resistor to ground between the two triodes of the 12ax7.
Where did you put the tone stack and volume control? Did you put the volume control in place of R7 the 220K to ground into the second triode?

I know a lot of questions...

[Blaze]

Is this any good for $180.00 ?

http://guitars.musiciansfriend.com/product/Crate-V-Series-V33H-33W-Tube-Guitar-Amp-Head?sku=487052




http://img3.musiciansfriend.com/dbase/pics/products/9/7/2/506972.jpg

[SciHi]

Is this any good for $180.00 ?



I had a v33 head, they have some issues stock but lots of work has been done on mods over at HC, ppwatt, and TGP. Dvnator has a website with his mod, Verne Andru has a thread on HC http://acapella.harmony-central.com/showthread.php?t=2118282 and wagdog and Steeve A (blueguitar.org) have versions of a slo mod for the v33. Cleans are good stock, overdrive channel needs work. Then with the mods, both are great.

[Blaze]

Standard

saTZkY9qzQE


Modded

C5hzsdio3KU&feature

[Tomko]

Rock Mumbles
The answer to your first question is basically yes. I left in R10 (now 47K) and R11 (1 meg) and went straight into pin 7 V1B. R1 and R2 were bypassed/removed. From there out of pin 6 to Marshall 18 watt basic vol/tone circuit. Not sure if I came back in at R7 for grid load to V1A pin 2 or bypasssed R7 and went straight to pin 2. Could that be my problem? Is the vol/tone stack providing grid load and I don't need/want R7? Or do I need R7? I think now that I bypassed R7. It's been several days now and I don't remember or have the chassis with me. Only other change was R31 from 4.7K to 47K. I think I did that to try to get some headroom. Any help is appreciated. I might try changing R7 from 220K to 100K as you suggested if it's not bypassed. I did get some pots on order yesterday so hopefully it won't be to long.

[rock_mumbles]

Hello again Tomko,

It depends on your volume pot set up, R7 dumps some signal to ground to prevent you from overdriving the next triode, the 220K stock R7 in the V5 is already a pretty small value compared to some "normal" values, but that depends on the "grid resistor" in the circuit before it.

As a quick test, put a 500K resistor across your volume pot #1 to #3 terminals, sending signal to ground around your volume pot and see if your signal gets cleaned up any.

[Tomko]

Rock Mumbles
You got me thinking. R7 is the grid load resistor for the next triode. I wired in at R7 going to ground so it's still in the circuit. Classic designs all use the vol pot for the grid load to the second stage so it looks like I'm doubling up. What do you think? I think R7 should be removed and I should go straight into the next triode from the vol pot. What do you think? Vol pot is 250K. The first triode grid load resistor is R11 (1 meg). New pots are on the way. Thanks for the help.

[SDW]

would anyone be willing to mod my V5? i'd try to do it myself but i lack the tools / ability to read schematics

[jim p]

On the amp I have I am reading a screen grid voltage of over 300 volts and all the data sheets rate the EL84 for a maximum voltage of 300 volts anyone have an idea on this. For now I have increased the screen grid resistor R18 to 10k dropping the voltage by 40 volts to 285 so 5k would put it right at 300 volts. This change also lowered the tube gain lowering the plate current also.
The other thing I have going is some white noise I replaced the ceramic cap C3 with a 500 pF mica paralleled C15 with 80uF, paralleled C9 with a 47uF tant and tried two other EL84 tubes but still have it. Anyone else have this experience?
The other amp I have that has a 6V6GT as the output tube is so quiet I think I am only hearing the dc filament voltage on the output tube so may try changing it to DC.

In looking over the schematic again I think the real problem with the screen grid voltage is it is connected to the wrong location. It should be connected to the junction of R26, R25 and C16 I have not made this change yet but will and post the results.

[goonrick]

Hello all, new to the board. Great discussion here on this little amp.

My question is, what could we expect if we simply did away with the opamp section and made it all-tube. There's still tons to change out in the tube sectioin (moving the volume after the tone control, tweaking the cathode bias resistor, et al).

Since I normally get my drive from a stompbox, what could I expect were I to simply mod R1 and R2 values and jumper over from where R10 used to be?...

[goonrick]

On the amp I have I am reading a screen grid voltage of over 300 volts and all the data sheets rate the EL84 for a maximum voltage of 300 volts anyone have an idea on this....

Could we simply adjust R24 to bring the entire voltage down just a touch? I'm tempted to try to bring the entire voltage down to around 300V. Would there be any problems with doing that? Couldn't we experiment by putting a resistor in series with R24 (starting with 1 Meg) and determining the effects on voltage that way?

[jim p]

The idea of just jumpering past the op amp in basic form just remove R2 and C25 jumper from R 11 to R1 would still need a volume pot. Without adding a volume control the input level will be the volume not sure you will like that. If you want to throw away the volume pot or use it as gain pot you can convert the tone pot to a volume pot then have no tone control.

[jim p]

If you convert the B+ supply to a choke input filter by removing C14 this will drop the supply voltage down to approx 275 volts. I would not mess with R24 it is just in the amp to pull the supply down with power off to help prevent death due to shock. So the change would be to cut the positive of C14 out and connect it to the positive side of C15.

[goonrick]

The idea of just jumpering past the op amp in basic form just remove R2 and C25 jumper from R 11 to R1 would still need a volume pot. Without adding a volume control the input level will be the volume not sure you will like that. If you want to throw away the volume pot or use it as gain pot you can convert the tone pot to a volume pot then have no tone control.

Yeah, I would still put the volume pot in place of R15 and R27. What would you imagine the tone control being like if left alone, spare swapping C28 out for a smaller cap?

[goonrick]

If you convert the B+ supply to a choke input filter by removing C14 this will drop the supply voltage down to approx 275 volts. I would not mess with R24 it is just in the amp to pull the supply down with power off to help prevent death due to shock. So the change would be to cut the positive of C14 out and connect it to the positive side of C15.

Effectively placing C14 in parallel with C15 after the choke, right? I just want to be perfectly clear before I start hacking on this little amp.

[jim p]

Yes you will be paralleling C15 with C14 a switch instead might be neat you would get two power output levels.

[goonrick]

Thanks, Jim. You're a wealth of information.

[jim p]

The screen grid resistor is attached to the wrong location on the PCB it should be on the other side of R25 (junction R25 R26 and C16). This will lower the screen grid voltage closer to (right at) its maximum rating of 300 volts. Best if you have the pcb out is to also replace R25 with a 7.5 to 10 k ohm resistor (approx 4ma across R25).

[jim p]

Another way to modify the amp would be to use the tone pot for a volume pot and the volume pot for a gain pot. This involves no cuts just jumpers and removing components with one being replaced (C24)
1) Remove PCB from chassis
2) Remove R13 C26 C24( to replace with 47nf for more bass or keep as is if you wish) C6 C5 C4 and R27
3) Replace C24 with a 47nf
4) Jumper junction of C6 C5 and CW2 (tone pot) to junction of R27 and R15
That’s it now the volume pot will control the gain of 2nd stage op amp for overdrive and the tone pot will control the volume.

[Big K]

Outstanding information!!!! But it makes my head hurt and tempts me to switch from coffee to vodka this morning with all the electrical theory.. I thought being able to solder effectively enough to swap out switches, pots and pickups made me feel like a genius when it all works but you amp modder guys are on a whole nother level :master: :master: :master: :master:
Thanks for all the shared information!

[tunghaichuan]

Just as a heads up, I got the new flyer from Guitar Center with the V5 priced at $79. My flyer came with a 10% off coupon, so the V5 is a pretty good deal from GC right now. :AOK:

tung

[jim p]

What to do with the stock V5 speaker? Now I hope you aren’t going to sell it to someone so why not use it as a testing load for the amplifier. I put one of those cheep ¼ inch cables on it packed some fiberglass around it and put it in the box the amp came in. So now instead of just looking at the output with a resistor as a load I have a speaker instead. There is quite a difference in the waveforms on the scope between the resistor and the speaker. With a square wave you can see overshoot with the speaker you do not see with a resistor. Also you won’t drive everyone crazy (cats, dogs and neighbors)

[jim p]

Has anyone made the supply a choke input yet, just want to know exact voltage they are getting at C15+. I may want to make the same mod on one of my amps. This would also free up Junction of C16 R26 and R25 as the decoupling for the second triode. Also if the voltage is low enough can leave the screen grid connection stock.
Found with the volume control after the tone stack at minimum you still get signal at the output of the amp. I think this is due to not having separate decoupling on both the first and second triode. So being able to move R6 to the other side of R26 would cure this as long as it is not used for the screen grid.

[goonrick]

Has anyone made the supply a choke input yet, just want to know exact voltage they are getting at C15+. I may want to make the same mod on one of my amps. This would also free up Junction of C16 R26 and R25 as the decoupling for the second triode. Also if the voltage is low enough can leave the screen grid connection stock.
Found with the volume control after the tone stack at minimum you still get signal at the output of the amp. I think this is due to not having separate decoupling on both the first and second triode. So being able to move R6 to the other side of R26 would cure this as long as it is not used for the screen grid.

Haven't done it yet, as I'm waiting on some components to ship. I'll be sure to post what voltages I get when I do though.

[goonrick]

Jim,

I did the choke input mod and am getting 296V at C15 plus. Is that about what we were shooting for?

[jim p]

Around 295 volts sounds right it should have been close to peak with the capacitor input (240 rms x 1.4 = 335 volts). With the choke that would drop to 335 volts X 0.89 approx 295 volts.
Do you have both tube operating? Should check to see if choke is running hot at all. I ran a simulation and the power in the choke is higher then the stock Pi filter but should just run warm to touch?
Were you looking to lower the voltage below what you now have?

[timothymegg]

I just got this little guy. The speaker sounds pretty bad but, I hooked it up to a 412 cab and it sounds much better. I would like to do some of the mods posted on here but, I can't decide between deafguy and jp? Jp is more defined but, the deafguy mod seems easier and more class A without an opamp. Any comments? Also, anyone have any experience with adding a triode switch and how to do it? One last thing, does this amp need to be biased?
Peace,
Timothy

[jim p]

Haven’t made this mod myself but have simulated it with vacuum tube models and a jfet model. If you go without the op amp the tone control is just a treble cut no boost. The op amp was the treble boost (pre emphasis). This circuit has C501 a 1nf across a 330k ohm resistor that gives you a boost when the tone pot is at full treble. You can change the operating point by changing the values of both C501 and C502 keep the ratio at 1 to1.5 ( 1nf and 1.5nf) or maybe 1to1 (1nf and 1nf) I would stay in the range of 1nf lowest value used 3-4nf highest value Lower value equal to higher frequency operating point , higher value moves it towards the bass end.

[jim p]

The op amp used in this amplifier is in almost every stomp and effects box made. It is cheep and the specifications are fine, this stuff is AM radio frequency response realm 5 kHz max (modern op-amps go into the gigahertz range). The input impedance is higher then the 12AX7 so it will not rob the high frequencies from you pickups if you are going straight in. Once you put a box between the amp and the guitar you are not all tube. With the circuit as is or with the changes I have posted you also have a cap in series to help cut out the 60Hz that the guitar is picking up( also you can reduce bass if you want). The op amp also provides the treble boost for the tone control to work as both treble cut and boost. I have kept the gain of the op amp to a minimum so with overdrive the first stage tube will be clipping not the op amp.

But still some will prefer to have no solid state components in there signal path so I have posted a tone stack to use with the op amp removed.
Remember the people that first designed guitar amplifiers in some cases were TV and radio repairmen so it is not an exact science and nothing to get hung up about. But what they did created the sound we have come to love. Wonder how things would be if the transistor existed before the tube?

PS If you look at the schematic for the Fender Hot Rod Deluxe this op amp is used in four locations Line out, Line in, reverb drive (poor choice for that) and reverb recovery. Line out and line in are in the signal path.

[rock_mumbles]

I would like to do some of the mods posted on here but, I can't decide between deafguy and jp? Jp is more defined but, the deafguy mod seems easier and more class A without an opamp. Any comments? Also, anyone have any experience with adding a triode switch and how to do it? One last thing, does this amp need to be biased?
Peace,
Timothy

Hello Timothy,
The bottom line the amp will sound like a "real" tube amp when converted, stock they sound like ... (you know). Take your time and study the V5 layout and the mods and pick one. The "all tube" mod will be simpler and you will end up with a simple two tube guitar amp, if you do jim p's mod you will have more stages (and in effect more sound/tone manipulation) in the preamp.

I've just started to do an "all tube" mod to my V5 with a simple tone stack and volume control where the stock tone stack is placed. I want to do it without cutting any traces, by removing components and soldering new connections onto existing component pads (it could be converted later to something different if I wanted to change it). When I get done I intend to post a color coded "mod" layout that shows the parts to remove and how to connect the new components.

EDIT: I changed the above wording, because I think people could take my intention in the original statement in a wrong way, Sorry guys I should have been more careful with what I posted.

As far as your question regarding biasing, what I think you are asking is if the amp needs to be have the bias adjusted when the output tube is changed, the answer is no. The V5 is a cathode biased SE (single ended) amp (as are most small two tube amps) and as such does not have an adjustable bias, so you just pull one tube out and plug in another. That does not mean that the bias is correct out of the box, one of the "correction" mods for Epiphone Valve Juniors is to replace the EL84 cathode resistor with a larger value so the tube is not pushed quite so hard.

[goonrick]

I ended up doing an amalgam between the two mod types and am pretty happy with the results. I bypassed the op-amp stage and made a typical two tube amp. I also followed jp's recommendations on tweaking the output section and power supply and the amp is running stably and sounding damn good.

I would say the all tube mod gives you less to work with in the way of preamp tones, but it does the screaming tube amp thing very well when driven with an overdrive pedal. I was shooting for a small amp that would do an acceptable job of copping a big amp tone and I got it. The one downside, and this may be inherent to all amps of this size, is that there's not a lot of clean headroom and so you're not really going to get inspiring clean tones from the amp. That's okay with me because I've got other amps that do the clean thing very, very well (Lab Series L5, DI's, etc.).

I set out from the beginning to have an amp that would conjure some class A tube mojo in a small and relatively low volume package. I'd say I got it. I will also really enjoy capturing the overdriven tones on recordings. It sounds nothing short of excellent for what it is.

BTW, I ended up switching a bunch of tubes (12AX7s, 12AT7, etc.) and settled on the 12DW7. It's an AX front triode and an AU second triode. You can get a currently manufactured DW at eurotubes and I highly recommend it. It brought out the best of my lil' killer.

[jim p]

Was asking if the choke was getting warm when amp is converted to a choke input filter. Also what is the amplifier noise like? The amp I have with stock Pi filter is so quiet you don't know it is on.
Regarding headroom the amp I modified is fine did change 12AX7 to an Electro-Harmonix from the stock Sovtek. You can see by looking at the EH that it is not just a relabeled Sovetek.
What speakers have you played the amp through?

[goonrick]

Was asking if the choke was getting warm when amp is converted to a choke input filter. Also what is the amplifier noise like? The amp I have with stock Pi filter is so quiet you don't know it is on.
Regarding headroom the amp I modified is fine did change 12AX7 to an Electro-Harmonix from the stock Sovtek. You can see by looking at the EH that it is not just a relabeled Sovetek.
What speakers have you played the amp through?

Haven't checked on the choke. The amp has a low level 60 Hz hum (no buzz though) that it had since the moment I first plugged it in. It really is so low by comparison of the guitar signal that I'm not worried about it. From looking at the schematic, it appears that they used AC voltage on the power tube filament, and I'm betting this is the source of the noise. No hum reducing resistors to ground or anything. I looked the PC board over and it is too much trouble to change, so I'm not going to worry about it.

I'll pull the amp chassis from the cabinet and operate it at full volume for a while and check the choke temperature and report back.

BTW, I've plugged it into a 1 X 12" cabinet loaded with a Jensen Mod 12-70 and it sounds fantastic. I swapped the internal crate crap 8-30 for a Laney HH Invader speaker and a huge improvement there as well. It gets a nice, boxy tone which I expect from the type of enclosure it is. I simply love it.

[goonrick]

OK. After about 10 straight minutes of high gain playing, the choke is cool to the touch. I started out with the multimeter and temp probe ready, but since it's not even warm to the touch I skipped actually taking a reading. I'd say the choke input mod is stable.

[jim p]

OK. After about 10 straight minutes of high gain playing, the choke is cool to the touch. I started out with the multimeter and temp probe ready, but since it's not even warm to the touch I skipped actually taking a reading. I'd say the choke input mod is stable.

When I ran a circuit simulation it gave me 5 watts on the choke but I have been fooled by circuit simulations before. The ripple was higher in the choke input simulation also so the amp noise maybe higher from that. The amp I changed to a 6V6GT has no noticeable noise the other one may have a bad filter cap so it is hard to tell. For head room you could try some feedback on the triode stages say 27 to 40 pf (300 volt) from plate to grid. Not that I am totally pushing op amps but the one stage was inverting so you could go less then unity (X 1) if that was in the amp. Also you could do a resistor capacitor feedback on the input triode and really drop gain but would need the op amp as an input buffer for that.

[jim p]

For the speaker on the two V5 amps I have modified I have used Weber speakers in both the price is great and I think Weber designs speakers with tubes in mind. There is a lot more interaction between amp and speaker with a tube amp especially a single ended output type like this one. If you think of the speaker as walking a dog this type of amp is like having a six year old walk an Irish setter the dog will call the shots in some cases. While a push pull tube amp will move up to being a 12 year old walking the dog and a solid state amp is giving the job to a linebacker. A tube amp has high output impedance so the parasitic components of the speaker inductance and capacitance (also the transformers inductance and capacitance) have a greater effect on the output sound. You can see this if you have an oscilloscope and signal generator looking at the output with a speaker for the load vs. a resistor. The Ted Weber web site has a Q and A section that has a lot of good information there are also sound clips. One more thing they have is an amp load that is a speaker motor the microMass this would be a better way of overdriving the amp vs. a resistor and it has a line out and tone control.
If you have yet to buy am amp MF has Weber speakers so you could get both at the same time and save shipping.

[rock_mumbles]

A friend has an all tube (modded) V5 with a Weber Sig 10 ceramic in it, it sounds a whole lot better than the stock speaker, but today just for grins I hooked up his custom made harp amp cabinet with a Weber sig 8S alnico, it sounded a lot less "boxy" than the crate v5 with the Sig 10 ceramic and had a fuller sound. I would guess that's due to the much better speaker cabinet and smoother sounding alnico speaker.

The Weber Signature speakers are great values for the money, the 10" signature ceramic speaker fits into the V5 cabinet without any modifications. I have an Eminence 10" alnico (an older 1028 maybe) in my V5 it sounds better than the stock speaker, but I haven't tried it with an all tube mod yet, so I'm looking forward to see how it is with a modded amp

[deafelectromark]

Hi Guys,
I have just read all the comments on this thread, and it looks like many of you are finding that this amplifier is a sleeper and can sound good if a few things can be changed. I thought I would drop a line here and tell you my reaction to all the stuff that is suggested here.
First thing (almost always) the speaker must go. it's cheap and plastic and would make a great speaker for the beach or camping. I am sure the cone could withstand water, but the sound is very unmusical for serious playing.
Second thing is that adding more parts, or trying to make a 'booster box' in the amp with the 'provided' op-amp is more technical than most owners could do confidently. Changes should be in small steps so that you know what it is that you did that made (or lost) that sound.
I will summarize my mod again for those who did not catch it in an earlier listing. I am not an Electronics Designer of Analog Audio, but I have been blowing up stuff before I was ten and did earn a Electronics Technician Certificate to fill in some of the things that I didn't know (about theory, design, etc,) and have worked in TV repair, High-End Hi-Fi ($$$) and custom installations while building, testing and tweaking amps.
I tend to over mod things and it becomes less satisfying to keep on modding things to death. Trying to make a cheap little amp sound like a Marshall stack is not going to happen. But if you want to get much better sound for the fewest bucks, you need to get the 'sand' out of the circuit. I want to be connected to the speaker, not dealing with quantum leaps inside a plastic part.
When the op amp was removed, there was very little gain to play with. You can get output tube distortion if you play it hard, with hot pickups and perhaps your favorite stomp box. I feel that some of the best distortion comes from those little boxes on the floor. 2 tubes are not going to get you a lot of gain (unlike my Epiphone VJ that could through careful parts section) so why try and make things harder for the amp, your time and money, and your general satisfaction of PLAYING, not tweaking. I do both- and I do admit I play MUCH more than I tinker. My amp sounds very good, and there isn't anything in it to make it solid-state, but I do some tricks in front of it.
My pedal layout in guitar into a homemade tube distortion box with one 12AX7 in it, then a dbx 119 compressor/expander, and then to a Picoverb for lushness. That all goes in the to the amp with the controls the way they are printed (stock look) and no other holes to drill, etc.
Get a copy of the schematic and layout and just try this if you really want all-tube sound. If you want metal, or loud headroom, you will not get it from this amp. But it is a great case, chassis and transformers just begging to make music.
Begin by cutting the trace after the input jack leaving R10,R11 for input loading. This will be just before pin 3 of op amp. Run a short length of coax from there to pin 2 of the 12AX7, and ground this wire at only one end (to prevent ground loops).
You will be cutting the volume pot out of the circuit and reroute wires as follows-keep the tone control circuit for now).
Connect the middle wiper to pin 2 of 12AX7. Cut out the R7, 220K resistor and the pot will take it's place for the load and volume control BETWEEN the two 12AX7 halves (this is so your guitar and/or you stompbox can play clean into the preamp tube or to push it more into output stage distortion)
Connect the top of the control to the junction of R15, R29,and C28: and the bottom to ground. Cut out the 100K (R15) (or R27, 10K) Resistor(s) so that the second half of the preamp tube is driving the same load. So you are basically removing R15, R27 and R7. You can increase the gain by floating a highish value resistor between the grounded end of the volume control (or a 500K or more pot) which gives you more drive voltage out of the second stage of the preamp, but I left that the way it is because it does give me the balanced sound (clean and dirty) that I want.
No parts, but a few pieces of wire, a speaker, and your time.
If you don't feel comfortable doing this, I still offer to do it anyway you want. (shipping is least expensive if you just send me your board and i will do it all for you and ship it back to you ($5.00 shipping) you put the board back in. Alternately, you can take the chassis out of the box and ship that to me, so you don't have to do anything other than unscrewing it back together, and the shipping wont me too bad.
Mark (manoteal at cox dot net)

[jim p]

From my post stated the Weber alnico fits the V5 just need to remove the magnet cover if the speaker has one. When you say boxy how do you mean. An 8 inch speaker will have higher frequency response then a 10 so is it the high end? While the 10 will have more bass. The frequency response range relative to cone diameter is suppose to be speed of sound(13584 inches/sec in air) divided by diameter for high end and low frequency is that divided by 10. So the 10 inch is 13584 in/sec/10in for 1358 Hz to 1353/10 for 135 Hz low end above this and below are harmonics and the sound being distorted somewhat. From the numbers it looks that a guitar amp should have a 10 to 12 inch speaker for bass and a 6 inch speaker for treble but from the Weber Q and A it looks that they have tried to work around this in there speaker design.

[jim p]

I think there is some misunderstanding of the gain in this amplifier doing basic calculations total impedance at the plate of the input 12AX7 times transconductance it has a gain of approx of 30 to 40 (don’t want to figure exact with tone stack it is frequency dependent to the extreme). The second triode not loaded down by a tone stack has a gain of approx 60. Looking at the data sheet for an EL84 from Mullard circa 1961 (find at tubedata.org) you only need 4.4 volts rms for five watts out. So dividing 4.4 volts rms by 60 you need just 73mV going into the second tube for full volume. You will never overdrive the second tube at that rate. On the guitar end a note is suppose to produce 100mV rms while a chord is good for 1V rms. So if you plugged straight into the grid of the EL84 you could get ¼ output from a strummed chord. If you want to go basic you just need one triode and one pentode to go from guitar to transformer and speaker with gain to spare. Check out old amplifier schematics at schematic heaven they were one input pentode and one output pentode. I think using both triodes is done because they are there you get two may as well use them.
If you want a lot of gain use one triode as a current source load for the other that will get you close to the triodes amplification factor of 100.
So bottom line you always over drive the first tube when using overdrive along with or without the EL84 output tube. The tone stack is a gain killer for the first tube and the amp has more gain then is needed.

[rock_mumbles]

When you say boxy how do you mean. An 8 inch speaker will have higher frequency response then a 10 so is it the high end? While the 10 will have more bass.

Hi Jim, first thanks for all the modding info ...

I think that the above statement was addressed to me.

With the V5 I played with yesterday, the 10" ceramic sig in the V5 cabinet sounded more "megaphone" like (boxy - unnatural midrange from too small of a cabinet) than the alnico 8" sig that is in a larger semi-closed back cabinet. The 8" speaker has more bottom end in the "custom" harp amp cabinet than the larger 10" speaker in the stock V5 open back cabinet. This shows the effect of a good cabinet

[goonrick]

I think there is some misunderstanding of the gain in this amplifier doing basic calculations total impedance at the plate of the input 12AX7 times transconductance it has a gain of approx of 30 to 40 (don’t want to figure exact with tone stack it is frequency dependent to the extreme). The second triode not loaded down by a tone stack has a gain of approx 60. Looking at the data sheet for an EL84 from Mullard circa 1961 (find at tubedata.org) you only need 4.4 volts rms for five watts out. So dividing 4.4 volts rms by 60 you need just 73mV going into the second tube for full volume. You will never overdrive the second tube at that rate. On the guitar end a note is suppose to produce 100mV rms while a chord is good for 1V rms. So if you plugged straight into the grid of the EL84 you could get ¼ output from a strummed chord. If you want to go basic you just need one triode and one pentode to go from guitar to transformer and speaker with gain to spare. Check out old amplifier schematics at schematic heaven they were one input pentode and one output pentode. I think using both triodes is done because they are there you get two may as well use them.
If you want a lot of gain use one triode as a current source load for the other that will get you close to the triodes amplification factor of 100.
So bottom line you always over drive the first tube when using overdrive along with or without the EL84 output tube. The tone stack is a gain killer for the first tube and the amp has more gain then is needed.

Would removing the cathode capacitor on the first triode stage have enough of an effect to reduce how much that stage is being driven? Also, could one place a smaller value capacitor in its place to add high end emphasis so the tone stack can still cut and boost? Which value would you recommend to add a little sparkle?

Thanks for all the valuable info. I'm having a blast hacking into this little amp.

[jim p]

Would removing the cathode capacitor on the first triode stage have enough of an effect to reduce how much that stage is being driven? Also, could one place a smaller value capacitor in its place to add high end emphasis so the tone stack can still cut and boost? Which value would you recommend to add a little sparkle?

Thanks for all the valuable info. I'm having a blast hacking into this little amp.
I posted a schematic for an all tube tone stack what you want is a voltage divider where the bass has more resistance to deal with then the treble. So in that schematic you will see the 330k with 22k and 1nf across the low frequency sees 330k so 40% of the signal at the plate is across the volume pot. Then at about 500 Hz the cap starts to short out the resistor so all the signal at the plate is across the volume pot while at the same time the tube is losing gain because the load resistance is going down (chicken and egg thing). With any tube tone stack connected to the plate as you change the tone you also change the gain. Life is easer when the tone stack is connected to a cathode follower. Removing the cathode bypass resistor will drop the tube gain but not as much as doing the tone stack as I have in the schematic. The value for the bypass to start at 500 Hz is 200nf. (Equal to 1/ 2 pi (6.28) X 500 Hz X 1.5 k ohms = 212nf)

[jim p]

I posted a schematic for an all tube tone stack what you want is a voltage divider where the bass has more resistance to deal with then the treble. So in that schematic you will see the 330k with 22k and 1nf across the low frequency sees 330k so 40% of the signal at the plate is across the volume pot. Then at about 500 Hz the cap starts to short out the resistor so all the signal at the plate is across the volume pot while at the same time the tube is losing gain because the load resistance is going down (chicken and egg thing). With any tube tone stack connected to the plate as you change the tone you also change the gain. Life is easer when the tone stack is connected to a cathode follower. Removing the cathode bypass resistor will drop the tube gain but not as much as doing the tone stack as I have in the schematic. The value for the bypass to start at 500 Hz is 200nf. (Equal to 1/ 2 pi (6.28) X 500 Hz X 1.5 k ohms = 212nf)

Looked around the web and in a design book I have and using the bypass cap to change the low frequency gain it may give you a factor of two difference in gain. It all depends on the total plate impedance the higher the impedance the less the effect. What does you tone stack volume pot ect look like as far as values and layout.

[goonrick]

Looked around the web and in a design book I have and using the bypass cap to change the low frequency gain it may give you a factor of two difference in gain. It all depends on the total plate impedance the higher the impedance the less the effect. What does you tone stack volume pot ect look like as far as values and layout.

Ok, what I've done is bypass the op-amp stage and routed the signal directly to the first triode stage. In that stage, I kept the resistor values the same but removed the cathode capacitor and placed a .02uF cap for brighness. I left the tone stack the same except I put the 56p cap that was in C27 and placed it in C28. I removed R15 and R27 and placed the volume potentiometer in place of them.

Apart from the preamp, I modified the output section according to your notes and have gotten rid of the harsh clipping that was occurring and every pin on the el84 measures within specifications. It is now a choke input power section which runs cool and I pulled C14 and C15 and put a larger supply cap in C15's spot.

As of right now, the amp sounds really good with a 12AT7. A 12AX7 gooses the gain a bit but sounds a bit darker, probably due to increases in internal resistance. I'm very happy with both the gain available and tone from the AT, though, and will keep it in there.

I still get a 60Hz hum at idle, which was present since before I modified it to be a choke input amp. I think I'll rectify and filter the filament voltage on the el84 simply by cutting and splicing into the lead wires coming off the power transformer. Shouldn't be too hard and the result will be an amp with DC filament voltages on both tubes.

[deafelectromark]

[/QUOTE]From the numbers it looks that a guitar amp should have a 10 to 12 inch speaker for bass and a 6 inch speaker for treble but from the Weber Q and A it looks that they have tried to work around this in there speaker design.[/QUOTE]

As many know, a 4 inch speaker can sound good and a 15 can sound bad. There are so many variables, you cannot work this out 'by the numbers'. The box the speaker is in, whether it is stuffed or not, ported, open or sealed, the amp, the effects used, the pickups used, where they are located and the controls for those pickups, the strings used, the guitar body characteristics, but MOSTLY- the players style and attack. How many of you tend to be extra light on the lower strings with the neck pickup and more intensely play on the bridge pickup? I am the sole determiner of what I want my sound to be, and adjust to the variables listed above. It is instinctive or at least learned through many years of playing. We play the way we want, and can get there many ways with many speakers/amp/pickup, etc. combination.
Science is fun, but it can only get you so far.
Deafelectro:rockon:

[jim p]

[QUOTE=goonrick]Ok, what I've done is bypass the op-amp stage and routed the signal directly to the first triode stage. In that stage, I kept the resistor values the same but removed the cathode capacitor and placed a .02uF cap for brighness. I left the tone stack the same except I put the 56p cap that was in C27 and placed it in C28. I removed R15 and R27 and placed the volume potentiometer in place of them.

You wrote that you have a 0.02 uf for a cathode bypass is this C1? 20nf (0.02uf) won't have an effect until approx 5kHz maybe you want 200nf (0.2uf) there. On your connection to pin 7 of the triode did you remove R2 the 100k to ground? Having R1 R10 and R11 as stock is ok but only want 100k in there with the op amp driving things. Me I don't like C4 the whole treble up then down thing as you go clockwise is odd to me. Both C5 and C28 should have little to no effect overall. Maybe I will simulate the first stage tone stack combination to get an idea of what would work best for treble boost regarding the cathode bypassing.

Attached a schematic with cathode bypassing for treble boost. Had to split the cathode resistor to keep gain difference down. Changed value of C5 it is off by factor of 10 looks like should be 220pf can also be omitted. Left out C4 and C28 C28 has little effect find C4 to be odd.

[goonrick]

You wrote that you have a 0.02 uf for a cathode bypass is this C1? 20nf (0.02uf) won't have an effect until approx 5kHz maybe you want 200nf (0.2uf) there. On your connection to pin 7 of the triode did you remove R2 the 100k to ground? Having R1 R10 and R11 as stock is ok but only want 100k in there with the op amp driving things. Me I don't like C4 the whole treble up then down thing as you go clockwise is odd to me. Both C5 and C28 should have little to no effect overall. Maybe I will simulate the first stage tone stack combination to get an idea of what would work best for treble boost regarding the cathode bypassing...

I removed R10 and jumpered to the junction of R1 and R2. I also changed R2 to 1 megohm.

On the cathode bypass cap, I only wanted the boost to be on the high end, and settled on that value after trying 2.2uF and .1uF. It really seemed to give it just enough high end without getting shrill and it took the gain of that triode stage down so that I could get more out of the later stages without overdriving it too much. It took the amp from behaving like a little Marshall to more like a champ. I intended all along to use an overdrive, so I'm pretty happy with the results.

I didn't mind the stock tone stack so much as it is a bit weird, but has a few useful positions and seems to mesh with the new arrangement of the first triode stage.

Other than the low-level 60Hz hum, the amp is sounding great.

Does the 6v6 you retrofitted feature a spiral filament? That may be one of the reasons yours is so whisper quiet when running at idle. I'm going to rectify and filter the el84's filament voltage in an attempt to cut down on the hum.

[deafelectromark]

In the above schematic that JimP shows, there is only 1/3 of the available voltage going into the next stage. His 220K+220K+ another 220K with volume control in parallel with the last 220K will suck off 2/3 of the signal AT LEAST. The output stage of that section will work with as low as 100K, but 220K would be better. I put the volume control where the last of his 220K resistors is connected in parallel withe the volume pot and eliminate the 2 upper resistors and the grid leak with one volume control (I used the stock one in the amp to prove that it was fine for this. If you were to prefer more gain, then a 500K or higher pot will load the preceding plate less and you can get (theoretically) more gain, but with less grid leak, you might also get more noise and/or biasing issues). Since the leak resistor (the one that goes from the grid to ground) is 220K, putting a 250K pot would not alter stability and getting rid of the 440K (220K x2) losses on the way to the volume control and grid of next stage. That was the worst part of the circuit in stock form- only the original was wasting 90% of the signal before passing it along. If you notice the part numbers starting with R1, R2, etc that are nearest to the tube part of the circuit are lower than the ones around the opamp, they appear to be added later. The opamp provided so much gain (supposed to be a good thing, right?) that the designers had to change things around to suit it. At one point in time, they probably had it closer to "correct", but some designer messed it up with the opamp 'sand' in the system. If you look at highly regarded and good sounding amps, simpler IS better.
Deafguy

[jim p]

If you call or e-mail crate for a schematic of the VC508 you will find that this amp is a stripped down version of it. The bad thing is they used the gain section (the op amp) for the volume control. Relative to how much signal you need going into the second triode it has a gain of approx 52 the maximum signal you could drive into the EL84 before grid current would occur is twice the cathode voltage (approx 15 volts) this is equal to 30 volts p-p. (By the data sheet 5 watts is with 12.3 volts p-p) so 0.58 volts p-p at the input to the second triode (will get you 30 V p-p). The lower the impedance of the tone stack the lower the gain of the first stage due to reflected impedance so lower values there will reduce the gain of the first stage. The capacitor values in the tone stack are biased on the impedance values in the stock circuit lower values should use larger value capacitors to compensate also the value of the tone pot may also need to be changed. The volume pot is a log pot so 12 o’clock is just 25k ohms (10%) out of 250k ohms with R7 in parallel that is 22.2k at the input to the second triode.
In the modifications that I have done the total gain of the op amp stages is -1.3 to correct for the pre emphasis circuit added at C25. Wanted to be certain that the first triode would clip well before the op amp. Also used the op amp as a high pass filter to limit frequencies below 120 Hz upper e string on a guitar is 190Hz helps cut down on that 60Hz hum.
This amp is not perfect if it were we not be buying it for around 90 bucks new (what did this cost to make?)
What is better then the VC805 is a 10 inch speaker stock it is junk but still the amp was only 90 bucks and you can choose one you like. The Pi filter on the plate supply, another thing price a choke for your amp it would cost you a minimum 16 bucks don’t have them on the valve jr’s I have.
+/- 15 volt power supplies which you can get +/- 18 volts from if you need more headroom. The VC508 used the 6.3 filament supply for just +/- 7 volts
A DC filament supply on the 12AX7.
So something you can mess with, make your own and costs less then you could buy the parts for yourself, cool.

PS: Regarding over all gain the first stage gain is approx 44 the second stage 52 the combined gain divided by the pot is 44 times 0.21 (pot in divider) times 52 equal to 480 the EL84 needs 4.4 rms for 5 watts so 4.4 divided by 480 equal to 9.1mV rms at input for full volume output if you remove R7 that goes to 828 for 5.0 mV rms. I think that is plenty of gain even if you are into tapping like Stanley Jordan.

[rock_mumbles]

Hello guys,

A couple of things, I've modded 3 Valve Juniors (all different) I like the sound of all three, the V5 has a lot more high end (too much to my ears) and also has a bit more gain than I'd like.

So, can anyone tell me what the purpose of C3 is? It's the 220pf cap across R16.

About the placement of R16. On a V5 R16 goes to ground after R31, what effect would there be if the 220K resistor was placed to ground between C7 and R31 instead of after R31?

Thanks!

[jim p]

Hello guys,

A couple of things, I've modded 3 Valve Juniors (all different) I like the sound of all three, the V5 has a lot more high end (too much to my ears) and also has a bit more gain than I'd like.

So, can anyone tell me what the purpose of C3 is? It's the 220pf cap across R16.

About the placement of R16. On a V5 R16 goes to ground after R31, what effect would there be if the 220K resistor was placed to ground between C7 and R31 instead of after R31?

Thanks!
C3 acrost R16 has no effect until approx 3.3 kHz it is out of the range of the normal frequencies from the guitar probably to roll things off when you overdrive the input. Moving R16 will have no real effect the pentode has little to no feedback capacitance (Miller effect) due to the screen grid between the plate and the cathode. A resistor in series with a triode is a different story there a resistor in series with the control grid will provide high frequency roll off due to plate to grid capacitance that is multiplied by the tube gain (Miller effect). R31 will limit the possible grid current and provide negative feedback if you overdrive the pentode (nasty thing to do to a tube the triode won’t like it either). What have you done with the op amp and tone stack? Without the op amp the tone control is just a treble cut there is no treble boost in the amp without the op amp or adding some. You could add a cap from the plate to the grid on the triodes this will lower the highs I would start at around 30 pF.
To drop the gain you could split the cathode resistors on the triodes I would have to work out the cathode impedance for the exact amount of change assume that it is 1.5k so if you remove bypass caps C1 or C8 you will half the gain of that stage ballpark current gain is 55 for each. So unbypassed that would drop to approx 28. If you use two resistors in series for the cathode resistor you can bypass one to adjust the gain say two 750 ohm resistors one bypassed would drop the gain by 0.67 X 55 = 37. (1500/1500 + 750 = 0.67) I was thinking someone might like to have this as a switch able function for the first triode. High gain when you want to over drive the tube low when you want more headroom

[jim p]

Other than the low-level 60Hz hum, the amp is sounding great.

Does the 6v6 you retrofitted feature a spiral filament? That may be one of the reasons yours is so whisper quiet when running at idle. I'm going to rectify and filter the el84's filament voltage in an attempt to cut down on the hum.
On the noise front is it for sure 60Hz as a sanity check and point of reference you can turn the amp volume down all the way plug in to the amp and put your finger on the tip of the jack then turn the volume up same frequency or higher from the amp? The filament supply is 60Hz while the plate supply is 120Hz so if it is power supply ripple on the plate it will be 120Hz. If you have added a standby switch another test would be to listen to the amplifier carefully right after you put it in standby. If the hum stops while the filter caps are still powering the amp it is the plate supply not the filament supply causing the noise the amp should still be active for a second or two after you flip the switch. On the 6V6GT filament winding I do not know but I think most tubes have opposing heater windings to prevent noise. The EL84 amp I moded doesn’t have any hum and the filter cap has self healed somewhat so that noise is down. The choke input may just be higher ripple then the pi filter supply. The Pi filter input cap would look like 28 ohms to ground to the 120 Hz and the choke would be 750 ohms in series followed by another cap that looks like 28 ohms. Plus the ripple into the choke would be small in amplititude due to the input cap.

[rock_mumbles]

Thanks for the info about C3 and R16 in post #111.


What have you done with the op amp and tone stack? Without the op amp the tone control is just a treble cut there is no treble boost in the amp without the op amp or adding some. You could add a cap from the plate to the grid on the triodes this will lower the highs I would start at around 30 pF.
To drop the gain you could split the cathode resistors on the triodes I would have to work out the cathode impedance for the exact amount of change assume that it is 1.5k so if you remove bypass caps C1 or C8 you will half the gain of that stage ballpark current gain is 55 for each. So unbypassed that would drop to approx 28. If you use two resistors in series for the cathode resistor you can bypass one to adjust the gain say two 750 ohm resistors one bypassed would drop the gain by 0.67 X 55 = 37. (1500/1500 + 750 = 0.67) I was thinking someone might like to have this as a switch able function for the first triode. High gain when you want to over drive the tube low when you want more headroom

I now have a blue eminence alnico 1028 speaker in my amp, and it's probably not really the amount of high end that bothers me it's the level of overdrive.

I have bypassed the op amp and have replaced C2 with a 0.022uf 715 Orange Drop which feeds into an 18 watt LiteIIb volume and tone control which then connects back to R7.

I just removed C8 on a friends V5 and wow did that clean it up, nice bright cleans at lower volumes that break up with higher volumes and harder attack, now it dimed is about the same gain as my amp on two or three. Since we both like more of a blues/classic rock sound, it's a lot better amp cleaned up.

The series cathode resistors sound really interesting. I could see that something between the bypassed gain level and the unbypassed gain level could be really useful. Would you "mess" with the gain on the first triode instead of the second? Why?? We were looking at a Princeton schematic so we removed the second bypass cap (I know that there's no cathode bypass cap because of the negative feedback in the princeton.) Would you still use the same bypass cap value, a 2.2uf like stock on the first triode?

Thanks again!

[amptweaker]

I would suspect that tantalum as your noise source.
I wouldn't worry too much about the high screen voltages as long as you use the stock Sovtek. These tubes look identical to the 6P14P and folks are using theme as 7189 subs. Besides, the 300 volts is a design center value for the 6BQ5.


On the amp I have I am reading a screen grid voltage of over 300 volts and all the data sheets rate the EL84 for a maximum voltage of 300 volts anyone have an idea on this. For now I have increased the screen grid resistor R16 to 10k dropping the voltage by 40 volts to 285 so 5k would put it right at 300 volts. This change also lowered the tube gain lowering the plate current also.
The other thing I have going is some white noise I replaced the ceramic cap C3 with a 500 pF mica paralleled C15 with 80uF, paralleled C9 with a 47uF tant and tried two other EL84 tubes but still have it. Anyone else have this experience?
The other amp I have that has a 6V6GT as the output tube is so quiet I think I am only hearing the dc filament voltage on the output tube so may try changing it to DC.

In looking over the schematic again I think the real problem with the screen grid voltage is it is connected to the wrong location. It should be connected to the junction of R26, R25 and C16 I have not made this change yet but will and post the results.

[amptweaker]

I would suspect that tantalum as your noise source.
I wouldn't worry too much about the high screen voltages as long as you use the stock Sovtek. These tubes look identical to the 6P14P and folks are using theme as 7189 subs. Besides, the 300 volts is a design center value for the 6BQ5.




On the amp I have I am reading a screen grid voltage of over 300 volts and all the data sheets rate the EL84 for a maximum voltage of 300 volts anyone have an idea on this. For now I have increased the screen grid resistor R16 to 10k dropping the voltage by 40 volts to 285 so 5k would put it right at 300 volts. This change also lowered the tube gain lowering the plate current also.
The other thing I have going is some white noise I replaced the ceramic cap C3 with a 500 pF mica paralleled C15 with 80uF, paralleled C9 with a 47uF tant and tried two other EL84 tubes but still have it. Anyone else have this experience?
The other amp I have that has a 6V6GT as the output tube is so quiet I think I am only hearing the dc filament voltage on the output tube so may try changing it to DC.

In looking over the schematic again I think the real problem with the screen grid voltage is it is connected to the wrong location. It should be connected to the junction of R26, R25 and C16 I have not made this change yet but will and post the results.

[jim p]

I would suspect that tantalum as your noise source.
I wouldn't worry too much about the high screen voltages as long as you use the stock Sovtek. These tubes look identical to the 6P14P and folks are using theme as 7189 subs. Besides, the 300 volts is a design center value for the 6BQ5.
I am not looking for maximum gain from the EL84 so moving the screen grid to what looks to be it's proper location works for me. I have it connected to a triode/pentode switch anyway. I was using the tant to try to stop the noise by paralleling the cap already in circuit with no effect. Believe it to be the cap after the choke it has started to quiet so the dielectric is self healing. If I get a chance will swap the 47uF cap moving it to the input to the choke. But I have reverb drive and recovery and triode/pentode switch hardwired to the pcb so it makes that more of a job.

[amptweaker]

I'm doing a lot of testing on my V5 before I start to mod.

One of the first things I did was to measure and then calculate the impedence of the output transformer.
It's about 3K at 8 ohms.

I thought this was a bit low, and checked the data on the EL84.
A look at the Rodenhuis book confirmed it was (he uses 4.5 to 7 k).

Feeding the grid of the EL84 with the signal generator and using a dummy loads, i scoped it out. The cathode was 14.3volts at idle.

With the load at 8 ohms I got a 10vpp signal that had very noticible second harmonic distortion.
That is only 1.5 watts!
Increasing the input signal caused the bias to increase (rectification effect).
Nearly 17 volt on the cathode when the other side of the wave began to round at near 17.5vpp out. (4.78 watts into 8 ohm)

Testing at a 16 ohm load, the waveform was much more linear up to 22.5 vpp with less than 1.5 volt increase on the cathode. (4 watts at 16 ohm).
Increasing the input signal gave more symetric clipping (3rd harmonic).

I hope that I have shown that depending on the flavor of distortion you prefer, it is ok to use either an 8 or 16 ohm speaker.
As for raw wattage you will lose a bit with the 16 ohm speaker, but if the 16 ohm speaker is more efficient than the 8 ohm you will gain it back in perceived loudness.

I don't think the stock speaker was designed to be efficient much less handle 30 watts...
(I could smell the voice coil burning when i hooked it up to a 25 watt amp to break it in!)

[amptweaker]

I am not looking for maximum gain from the EL84 so moving the screen grid to what looks to be it's proper location works for me.

I noticed the unused tap at R25 and R26 too.

Never know what kind of whackyness you'll find in a Crate.

Took a look at the screen grid while driving it hard and it does turn cherry red...

[jim p]

Thanks for the info about C3 and R16 in post #111.



I have bypassed the op amp and have replaced C2 with a 0.022uf 715 Orange Drop which feeds into an 18 watt LiteIIb volume and tone control which then connects back to R7.

I just removed C8 on a friends V5 and wow did that clean it up, nice bright cleans at lower volumes that break up with higher volumes and harder attack, now it dimed is about the same gain as my amp on two or three. Since we both like more of a blues/classic rock sound, it's a lot better amp cleaned up.

The series cathode resistors sound really interesting. I could see that something between the bypassed gain level and the unbypassed gain level could be really useful. Would you "mess" with the gain on the first triode instead of the second? Why?? We were looking at a Princeton schematic so we removed the second bypass cap (I know that there's no cathode bypass cap because of the negative feedback in the princeton.) Would you still use the same bypass cap value, a 2.2uf like stock on the first triode?

Thanks again!
Replacing C2 with a lower value should have increased the highs out of the amp (C8 being a high pass component) but this is dependent on the tone stack you have. Can I find a schematic for your tone stack on the web?
Removing C8 is interesting that should increase the high frequency range of the tube (reduce gain equals reduced Miller capacitance) but you probably now increase the setting on the volume pot thus the input resistance and are back to where you started in that regard. But having no bypass will add degenerative feedback so maybe the tube is more stable.
On the split bypass if you use it on the input triode and know you do not want to overdrive the amp you could set it for unbypassed this would lower the gain so no overdriving the tube. Also lower gain is lower Miller capacitance so you won’t loose the highs when plugged straight into the guitar from that. The tube response may also be a bit more stable from the feedback. Some people are posting that they are changing to a 12AY7 or 12AT7 for lower gain this may work just as well for them.
Then if you want to overdrive the input triode you would bypass the cathode resistor for full gain on the input triode. So you just need to connect the ground lead of the bypass capacitor to ground through a switch.
Also some unbypassed resistance in series with the cathode might make things more stable from the feedback it would provide I have to search to see if that has been done.
On the bypassing of the second triode it would just be to reduce overall gain to remove it, except as before it might provide stability. One thing that may or may not be a problem is both triodes share the same decoupling I think this is why you can get signal through the amp with the volume all the way down. Without the tone stack the signal from the first tube would be 180 degrees out of phase with the second but with it? So I am not sure that this may not be a problem?

[Songman68]

Step by step modifications done to Crate V5 amp

1) Remove the amplifier from cabinet. First remove speaker jack then the six screws holding back cover of amplifier then with amplifier upside down remove four screws two on each side of cabinet that hold amplifier chassis in cabinet. (Note: you may want to enlarge the holes slightly in sides of cabinet and on back cover to make reinstallation and future removal easier)

2) If you haven’t already done so (you do have this unplugged right?) get out a dc voltmeter the highest voltage in the amplifier is approx. 320 volts DC measure from chassis to R25 should be 0 to 15 volts if so you are safe. This amplifier has a bleeder resistor R25 so supplies should drop after power down.


3) Remove preamp (12AX7) and power tube (EL84 6BQ5) put them some where you wont break them.

4) Next remove knobs on front panel may require flat blade screwdriver and a thin piece of wood to work against to prevent scratching front panel. The pots are D shaft type walk then off gently. Then remove nuts holding pots and ¼ inch jack on front panel.


5) Now make note of all the connections to the PC board because you are going to remove them. If you have a digital camera now is a good time to use it. Also if you print out the schematic note wire color and location on it. The faston connectors J4 J5 J1 and J2 may be hard to remove don’t break them of pcb by working them back and fourth.

6) Next remove the six screws that hold PCB into chassis and take it out. (hope you are putting parts someplace you wont loose them)

PC Board modifications
(See attached pictures of mods and changes to schematic also pic DSCF0947.jpg in previous post is the pre emphasis mod the tone mod is incorrect in that post tie unused side of pot in tone control to wiper not ground or unconnected up to you)

1) You are going to be removing approx 10 parts. You will need solder, solder wick, soldering iron, needle nose pliers and desoldering tool. In manufacture the compnet leads have been bent so desolder a componet lead then straighten it before removing or you may damage PCB plated feedthrough.

2) This modification will use the two Op Amp stages for an input buffer and small gain to over come loss due to pre emphasis circuit that will be added. Desolder and remove volume pot from PCB. Next remove R13 this makes IC1-A a unity gain buffer. Remove C26, C24 and C27 replace C24 with a 47nF 50-100 volt poly cap.C24 sets the low frequency limit at input to the amplifier with 47nF this is approx 125 HZ 3db down (for more bass use 100nF). In the place of C27 install a 33k ¼ watt resistor this equals a gain of 1.22 for IC1-B (want to keep gain low so first stage tube will clip before the Op Amp with overdrive).


3) Pre emphasis circuit For the tone control to be able to cut, boost and be set for flat response the high frequencies need to be boosted first. So C25 needs to be removed if you want replaced or use it again for this mod. Install one lead of a 100nF 50-100 volt cap into plated hole (via) that is connected to pin 7 of IC1 in the second hole of C25 insert lead of 33k ohm ¼ watt resistor with a 10nf capacitor accost it then connect the other lead of the 33k resistor to the second lead of the 100nF capacitor. If you want full treble brighter you can lower value of R2

4) Tone stack and volume control Here we will put volume control after tone stack and first tube stage so you will be able to overdrive input tube and still control volume. Remove C5 C6 C28 and C4 Change C6 to a 22nF 50-100volt poly capacitor. (Here a lower value cap will raise where the tone control will cut the highs higher value will lower it.) Now the volume control remove R15 and R27 using the volume pot removed from the board you will need to bend the leads 90 degrees towards the back of the pot to attach 1 ½ inch wires to the three terminals of the pot. Also need to insulate PCB were pot was attached to prevent shorting (three layers of electrical tape works) looking at the front of the pot as use to be connected to the PCB the right side terminal connects to the plated hole C28 that connects to R29 the center terminal (wiper) connects to the plated hole of R27 that connects to R7 and control grid (pin 2) of the 12AX7. The last terminal goes to the plated hole of R27 that goes to ground. (note be careful the leads soldered to pot do not short to metal back shell of pot no sound out of amp)

5) Oscillating power tube in testing the amplifier found output did not clip symmetrically and oscillated when clipped. Based on the tube data sheets the cathode biasing is to high in value. Change R17 to 270-300 ohms 2-5 watt or parallel the 330 5 watt with another 1.5k ohm 2 watt (270 ohms)


6) That’s it now put it back together and be careful around high voltage always follow one hand rule working on tube amplifiers. The one hand rule is make sure other hand and body are not tied to ground other hand does all the probing. So tie meter or scope ground to the chassis ground then do all your measurements.

Other tweaks
From the way this amplifier is set up it may have had gain, tone and volume controls?
And they took the volume control out instead of the gain control so if you add a third 250k pot across TL01-B same as in the stock schematic this will be a gain control you should add a 27k resistor in series to set minimum gain at unity (1).

Lowest frequency amplified the stock value of C24 is to low 3db down at approx 270Hz the value in the mod is 47nF for 125Hz if you want you can go bigger 100nF but this may increase that annoying 60 Hz hum we have all come to love.

On the pre emphasis mod you can change the value of R2 to increase or decrease the brightness of the maximum tone. Higher value for R2 (stock 100k) will reduce the maximum lower value increase it. If you lower the value you may want to increase the gain in the Op Amp stage to offset the loss.

Tone control pot from my results the tone is flat at the 9 o’clock position so if you use a 100k (125K) pot for the tone control this will move it to the 12 o’clock position.
Changing where the tone control operates you can reduce the value of C6 to raise or lower where the tone control operates but you should change the value of the cap in the pre emphasis circuit also (10nF across 33k ohm).

It may be my lack of skills but I tried all of this and for some reason it didn't work right. I had really low volume and really bad distortion with the amp wide open.

[deafelectromark]

It may be my lack of skills but I tried all of this and for some reason it didn't work right. I had really low volume and really bad distortion with the amp wide open.\

It sounds like a lot of work to me, and I am an electronics technician. One of the main problems with doing a mod is to do them one at a time so you can see where you had success, or worse- catastrophe. If you put the amps (modded and unmodded) side by side, you should hear a big difference in the sound of each. But the question remains--exactly what circuit mod made the most improvement (happiness divided by dollars).
There is nothing wrong with taking a cheap and amp making it better and learning how all the parts relate to each other and to learn electronics. The fact that you are a member of the FRET is indicative of your passion to tinker and improve.
There is so much information on the websites about this stuff, it is hard to just say, " I want it to play loud and clean". It can't and it wont. Clean sound needs efficient speakers and/or powerful amps to keep them from distorting. You can play clean and soft- you are staying withing the amps power levels. If you need 50 or more watts for clrean and loud ya gotta go big. Dirty and small and reasonable levels for today's living is easy. Look at how many amps there are out there that sound good and can be made much better; but then you are getting into higher price level where a more expensive amp is really what you wanted and you needed in the FIRST PLACE. That is why I limit expenditures on small amps. Sure I could add hundreds of dollars to get all the best parts and the best circuit, But it still will sound different than someone's amp and cost more that a 'better amp'.
I have a saying on 18watt- Tone is subjective!
Mark

[jim p]

Thanks for the info about C3 and R16 in post #111.




I have bypassed the op amp and have replaced C2 with a 0.022uf 715 Orange Drop which feeds into an 18 watt LiteIIb volume and tone control which then connects back to R7.

I just removed C8 on a friends V5 and wow did that clean it up, nice bright cleans at lower volumes that break up with higher volumes and harder attack, now it dimed is about the same gain as my amp on two or three. Since we both like more of a blues/classic rock sound, it's a lot better amp cleaned up.


Thanks again!
I found a schematic for the amplifier that has the tone control that you have used I think. This is 500k log pot for tone 500k log for volume 500 pF at top of tone stack 10nF at bottom is that correct? In the schematic for the amp it is in it is input to a long tail pair or differential amplifier whatever you prefer to call it which most likely has less gain (need to work out gain for it) then the second triode you are connected to. First did you use the same values for the pots and caps? If you used the 250k pots in the amp the cap values will need to double. Also to offset the greater gain in this amp may need to reduce signal across this tone stack and volume control. If the mod was in the amplifier that you removed C8 on and it improved that backs that assumption. So you could put a resistor in series with the volume control and tone stack to reduce the signal across it. Another thing you could try is to reduce the signal at the grid of the EL84 by increasing R31 probably will need to remove or reduce C3 if you do that

[jim p]

It may be my lack of skills but I tried all of this and for some reason it didn't work right. I had really low volume and really bad distortion with the amp wide open.
What tools do you have to work with do you have a DMM, scope, signal generator ect. If you just have a meter can give you locations for ohmeter tests to see if things are wired correctly.
One quick possable problem is the volume pot shorted to it's self or the PCB if you have no insulation or the insulation on the PCB is broken. I had that happen once to me after having the board in and out to make a change.

[deafelectromark]

What tools do you have to work with do you have a DMM, scope, signal generator ect. If you just have a meter can give you locations for ohmeter tests to see if things are wired correctly.
One quick possable problem is the volume pot shorted to it's self or the PCB if you have no insulation or the insulation on the PCB is broken. I had that happen once to me after having the board in and out to make a change.

The most irritating thing that I have to deal with when making changes are cold solder joints (looks good but nothing gets through) and solder bridges that I make when I solder close to adjacent traces and the sound goes to lala land. I agree with JP that using only a meter should find all but the worst problems (like oscillations, grumbly hums, wolf tones and all that stuff- you really need a 'scope to see inside the circuit and pinpoint where the problems start).
Another very frustrating issue is much like what JP said, shorted or open parts, or parts that don't have the value printed on them in color code. Remember that some parts have a silver band or gold or on the end making them 1/10 or 1/100 of the color code value. Putting in a 0.3 ohm resistor is far from 3 ohms and things will get nasty and 'look OK'.
Dirt and corrosion has me scratching my head in most of the problems that I work on. Tarnish, rust, salty bridges, intermittent pots, and controls (switches) are almost ALWAYS the first thing that I check now and save myself from hours of 'exploratory surgery' and part replacement. Don't forget that the people who sell the parts and the manufacturers make mistakes and it can make you go loony when you put in a 'correct value part' and it still doesn't work and you spend hours looking elsewhere. New parts are always OK? No they are not. Even switches have been faulty- the least complex of the parts you use. Caveat Emptor!
Mark

[rock_mumbles]

I found a schematic for the amplifier that has the tone control that you have used I think. This is 500k log pot for tone 500k log for volume 500 pF at top of tone stack 10nF at bottom is that correct?

Yes that is the volume/tone control I used. I got the amp working like I want it today, I put a 150K resistor between C2 and the volume pot and a 470K from the volume pot side of the 150K to ground (effectively have a 250K volume pot). Now the amp works fine! BTW, I have removed C3.

Now I can have the second split cathode resistor bypassed on the first triode and have an on-off-on switch hooked up on the second triode to have full bypass (most gain) no bypass (lowest gain) or partial bypass (medium gain).

Now I'm pretty much OK with the amp, it's a nice little portable combo amp. It's not quite as powerful or quite as good sounding as my modded Valve Junior but I paid more for the Valve Junior Hammond 125ESE output transformer and mod kit than I paid for the V5.

Thanks again

[jim p]

Well I am working on my third V5 think I may do a full make over to a 6V6GT output tube and two 12AX7 for overdrive and cathode follower driven tone stack and reverb(op amp drive and recovery). Probably just make it a head instead of a combo amp. The 6V6 conversion saves you enough heater current to add the second 12AX7.
I looked at the turns ratio again and saw in another post that the impedance for a 8 ohm speaker to be a 4 to 5 k ohm plate load is wrong, that looks to be right. I measured it before and came up with 20:1 but talked myself out of it but that is what I am seeing now. For what it is worth the reflected impedance is the turns ratio squares times the load (20X20 = 400 X 8 ohms = 3200 ohms). Going by the Mullard data sheet you want 4.5 k to 5.25k at the plate approx 24:1 turns ratio. On the up side the triode mode is looking for a plate load of 3.5k so this transformer is good for the triode mode which is your lowest distortion mode if you are in to that sort of thing. But this is a single ended output and harmonic content is suppose to be what you are looking for if not you should go push pull or solid state. From what I see at the plate with a scope the distorted portion of the waveform is when the tube is off which is flyback time. When the tube turns off it is the magnetic field of the transformer collapsing that is going to drive the load think of it as a flywheel or water wheel the tube spins it up then stops and it keeps going for a while. But the speaker is a load on this so the less load the longer it spins so a 16 ohm speaker is less of a drag then an 8 ohm speaker. But a 16 ohm speaker is not a 16 ohm speaker and an 8 ohm is not 8 ohms either, that is there nominal or average impedance. So bottom line what are you looking for? A single ended output is suppose to give you second harmonic distortion for that fat sound if you undampen the output with a higher impedance you will reduce it and increase the third harmonic. Another thing to keep in mind a resistor is not a speaker to get a more realistic load you can do what I did and stuff the stock speaker in a box or Ted Weber makes a load that is a speaker with no cone.
Also looked at the cathode bias on this amp but I first moved the screen grid from its connection to J4 over to junction of R25, R26 and C16 where it should be. From testing on this tube the cathode resistor should be 270 ohms that resulted in a plate current of 38mA screen grid current of 4mA with approx 315 volts across the tube for 12 watts at the plate.
Has anyone thought of converting there amp over to being a RAT, if you remove the c and e from crate on the front of the amp you get a well centered RAT on the front. Or maybe you like that sleeper stock look.

[jim p]

Instead of running the ground lead of the capacitor used for switchable cathode bypassing back and fourth through the chassis I think it may be better to use a nmos fet switch. This way there should be less chance of noise pick up and you keep the ground loop tight around the cathode resistor. I have attached a schematic that shows the basic set-up. I may also use this same circuit to parallel the output tube cathode bias resistor when switching between triode and pentode mode. In that case I will use a four or five pole double throw switch for isolation from the screen grid connection with a two pole switch I think a high voltage arc might occour within the switch. The BS270 fets in the schematic are available from Mouser electronics for 19 cents each.

[jim p]

Yes that is the volume/tone control I used. I got the amp working like I want it today, I put a 150K resistor between C2 and the volume pot and a 470K from the volume pot side of the 150K to ground (effectively have a 250K volume pot). Now the amp works fine! BTW, I have removed C3.

Now I can have the second split cathode resistor bypassed on the first triode and have an on-off-on switch hooked up on the second triode to have full bypass (most gain) no bypass (lowest gain) or partial bypass (medium gain).

Now I'm pretty much OK with the amp, it's a nice little portable combo amp. It's not quite as powerful or quite as good sounding as my modded Valve Junior but I paid more for the Valve Junior Hammond 125ESE output transformer and mod kit than I paid for the V5.

Thanks again
I calculated the gain of the differential pair used as a phase splitter and it should be approx 26. That is close to the same gain as the second triode without cathode bypassing in the V5 (gain 25). One thing about the Lite II that looks wrong is that the plate load resistors are equal values in the phase splitter. From what I have read and simulated the plate load resistor on the input tube (R6) should be approx 20% smaller then the other plate load resistor to have equal amplititude signals. Anyway the V5 overall gain should be the same as the Lite II with the input triode bypassed and the second triode unbypassed.

[larryx]

:confused: Hello folks,
Well I'm just another confused and frustrated Crate V-5 owner. I like alot of V-5 owners am looking for some (simple) mod instructions. Not the long winded ones written by technological geniuses. I'm talkin about something the average guitar player who can read tab and paint by numbers can do! I'm getting tired of reading about Jonnie Multimeter and his triumph over bypassing the op amp section and making his personal CrateV-5 an all tube circuit. While the rest of us dread the day we bought one! How about someone with this knowledge sharing some easy to understand mods. Information like what resister and capacitors do we change? R-? and C-?. And what values do we change them to? Alot of us guitar players are just looking for a solution to get a good sound out of our V-5's. Is anyone willing to put together some ((easy to understand directions)) for making these amps worth owning ? Most of the info out there is way to difficult to understand. I CAN HEAR THE AMEN BROTHER!, COMING FROM THE NON TECHY GUITAR PLAYER CROWD OUT THERE ON THE FRET!!!

Many Thanks to who ever steps up!!!

[SciHi]

:confused: ...Well I'm just another confused and frustrated Crate V-5 owner...

I spent the last couple days playing around with a v5, I recently completed extensive mods to my crate v18 and figured the v5 would be a piece of cake. BUT the v5 is pretty screwed up. As bad as people said the v18 sounded, it was just a couple of resistors and capacitors away from great sounds. The v5 however, is a trainwreck, and not in a good way. There are no really simple fixes because, #1 it doesn't have a volume control and #2 it doesn't have a working tone stack. So those two things need fixed before you can worry about any small tweaks here or there.

What is currently called volume is a gain on the opamp. It is fine to have it there, just don't ever turn it up! The amp needs a volume control, preferrably between the two tube stages of the preamp. So you either pull the existing tone pot, fix the gain on the opamp as suggested by Jim P, or pull the pot and totally bypass the opamp totally, running the input to the first stage of the preamp tube. Your option, you get to choose. Jim P does give step by step instruction so you can keep the opamp working and move the volume control to the correct place. If you want to try and locate another pot on the amp somewhere, then you could add it for volume control and leave the gain on the opamp (this is more like the earlier models of this amp). So that is a third option to fix the "no true volume control."

To fix the tone stack, Jim P has step by step instructions and they are about the easiest. But many different one knob tone stacks, such as the tweed could be adopted. You could even add 2 (or 3) pot tone stacks by using dual pots, such as Verne A. posted on HC for the Palomino 8, a close cousin to this amp. Pick your favorite, or follow Jim P step by step instructions for the simplest. Once these two major problems are fixed, then you can start simple resistor and cap changes to voice the amp to your liking.

The amp I played with was modded by Rock_Mumbles. He jumpered the opamp, used a modified liteII tone stack, and added switchable cap bypass on v1b cathode. Real nice mod, very close to a well modded VJ. Maybe we can shame Professor Mumbles in posting his modified schematic drawing...

[rock_mumbles]

:confused: Hello folks,
Well I'm just another confused and frustrated Crate V-5 owner. I like alot of V-5 owners am looking for some (simple) mod instructions...

Like Scihibmxer posted, unfortunately the Crate V5 is not as easy to mod as some other amps I've modded in the last year, you won't gain much by just changing out a resistor or cap like other amps. We both thought - a nice little combo amp for a decent price, only 5 watts so it won't make quite as much noise in the house as the 18 watt amps, it's a 2 tube amp should be no problem to modify.
I probably spent about 10 hours working on my V5 last week (I was on spring break), so I am also "Confused And Frustrated"
My response to the V5 after the initial mods (bypassing the op amp and adding in the volume/tone control) "what the heck is up with you???" I spent way too much time for very little progress. I finally have the amp so it's OK as a test amp for guitars and pedals.

So...

What kind of guitar do you play??? (my modded V5 is OK with my Tele but doesn't sound very good at all with my brother's Dimarzio humbuckers, it would need to be throttled back for humbuckers)

What do you want your amp to do??? (you have to remember it's a simple 2 tube amp so do you want some cleans with breakup or completely overdriven - for complete overdriven sound listen to 777funks modded amps he sells on ebay, they are a one-trick pony)

In my opinion the speaker has to be replaced, what kind of speaker are you thinking about??? (the Weber Sig 10 or Sig 10S are good sounding reasonably priced speakers)

The things I have done that I could help you with is an easy way to:
(a) bypass the op amp and correct the input jack. (this involves removing the volume pot )
(b) remove the stock tone stack, and move the volume control and add a simple one knob tone control into the circuit where the stock tone stack was.
(c) deal with the amp's gain, if it has too much gain for you.

I wouldn't work on the amp unless you have some spare 16mm pots (and some new knobs handy) it's really easy to mess up the pots desoldering and soldering them. I help out at a friends music store so I have access to lots of parts and a good solder station, volt meters etc., so when I burned out the volume pot soldering the ground wire on, I just got another one out of the parts drawer.

You'll also need a couple of caps for the new tone stack three or four values of resistors and maybe a new 400V capacitor that goes in the circuit before the volume/tone stack.

Again, I can help you with the mods I have done, but anything else is just a guess. If you're interested, I'll put up a mod layout and parts list.

[jim p]

The most basic mod you can do that should have a significant change to the amp (with exception of replacing the speaker) is to use the tone pot for a volume pot and keep the volume pot for a gain control. I posted a list of components to remove and replace for this and how to jumper the tone pot to the control grid of the second triode for a volume control. I could draw up a small schematic to show what the changes are if someone wants. But a basic thing you may need to know is how to read a schematic and I will guess you might be able to read about just that subject on that thing they call the WEB. If you don’t know about something here open a new tab and Google it. Where do you find those tabs you have been using eh? So Google resistor, capacitor, and inductor heck you can find sections of college courses on electronics on this web thing.
Anyway doing the tone to volume control mod you do not have to remove the pots so no chance of damage to them. Other amps out there do not have a tone control so? The gain op amp set up in this amp is better then the Crate VC508 because that only had +/- 7 volt supplies which may not have been enough headroom to prevent clipping in the op amp before the tube.

[Tomko]

So you can decrease the voltages on the EL84 by increasing the cathode bias resistor? I'm still over 330 volts on the plate and screen grid but the amp works fine. I see the cathode bias resistor for the EL84 is R17, 330 ohm, 5 watt. What would you increase it to to get the voltages below 300v?
Also, you keep saying increase R16 to 10K but it is already 220K. Is this a typo, mistake or what? You're confusing me- easy to do.

[goonrick]

So you can decrease the voltages on the EL84 by increasing the cathode bias resistor? I'm still over 330 volts on the plate and screen grid but the amp works fine. I see the cathode bias resistor for the EL84 is R17, 330 ohm, 5 watt. What would you increase it to to get the voltages below 300v?
Also, you keep saying increase R16 to 10K but it is already 220K. Is this a typo, mistake or what? You're confusing me- easy to do.

If you look through this thread, you can see where Jim P recommended to make it a choke input power supply by ganging C14 and C15. I did this by removing C14 and replacing C15 with a larger cap. It did reduce the B+ by a number of volts and it got the screen running at around 296V on my amp.

I believe there were changes to the screen resistor and R25 as well, though I don't recall offhand what the changes were.

[Tomko]

Thanks for the info Goonrick but I really don't want to mess with the filter caps and I have no replacements for them (nor can you get them in this town) so I think I'll try a 4.7K grid screen resistor for the EL84 and see how what it does. Hope I don't mess something else up!

[jim p]

So you can decrease the voltages on the EL84 by increasing the cathode bias resistor? I'm still over 330 volts on the plate and screen grid but the amp works fine. I see the cathode bias resistor for the EL84 is R17, 330 ohm, 5 watt. What would you increase it to to get the voltages below 300v?
Also, you keep saying increase R16 to 10K but it is already 220K. Is this a typo, mistake or what? You're confusing me- easy to do.
If this is a question to me I lowered the cathode bias resistor to get to 12 watts at the plate of the EL84. The stock value is conservative probably for tube to tube variation (so plate current is low). Regarding the value of 10k I did mean R18 but what should be done is to remove the side of R18 connected to J4 and connect it to the junction of R26 R25 and C16+ this is where it should be (look at schematic). Bad thing is you will have to remove some of that clear RTV they gooped everywhere to get to this junction. Also would be best to change R25 to 7.5k (6ma across R25, this is from 4ma screen current and 2ma from 12AX7) should equal a 45 volt drop from the voltage at J4
To explain my changing the cathode bias resistor you can calculate the cathode current by the voltage across it (Vk/Rk = Ik) subtract 4ma for screen current(what it is in most cases) to get the plate current. Then the plate dissipation is the voltage across the tube (plate voltage minus cathode voltage) times the plate current.
On this amp with a 275 ohm resistor I had 11.4 volts at the cathode equal to 41.5mA – 4ma screen current for a plate current of 37.5mA with 326 volts at the plate minus 11.4 cathode voltage for 315 volts across the tube. So 315 volts times 37.5mA for 11.8 Watts.
Best way to try lower values is to parallel the resistor with a higher value if you know how to calculate resistors in parallel. A good method is reciprocal method example R1 in parallel with R2 there total resistance is 1/(1/R1 + 1/R2) = Rtotal What you are doing this way is changing them into the current that would be through them with one volt adding the total current then dividing the one volt by the current to get the resistance. Surf the web for more on calculating resistors in parallel for a better understanding.

[rock_mumbles]

... Regarding the value of 10k I did mean R18 but what should be done is to remove the side of R18 connected to J4 and connect it to the junction of R26 R25 and C16+ this is where it should be (look at schematic). ...

Hi Jim,

Would it help to add a 22uf 450V filter cap (to ground) in the B+ supply where R18 was connected to J4?

I just happen to have several caps without amp "homes".

Thanks

[Tomko]

Yes the question about R16 going to 10K (or 5K) was meant for you. I think you were the only one who mentioned it. I realized later you meant R18 after re-reading the whole thread and checking the schematic. I picked up a 4.7K today to try. I tried to hookup at R25 but must have ruined the resistor removing the RTV as all I got was a bunch of noise. Put it back the way it was and still got a bunch of noise. So now I will be replacing R25. I do know how to calculate both resistors and capacitors in series and parallel. Had Basic Electronics 101 in route to BSME. I am not an expert when it comes to electronics and I don't have anything but a basic working knowledge of amps (4 books), a soldering iron and a multimeter. I have worked extensively on my BF Bandmaster and they sure are easier to work on than PCB amps and in particular the V5. It was bad in its original form. I went for the basic tube amp with a 18 watt vol/tone circuit in between the two triodes. Had it working fine until I tried to hookup at R25.:thwap: Thanks for your knowledge and especially the explanation of the cathode bias.

[jim p]

Yes the question about R16 going to 10K (or 5K) was meant for you. I think you were the only one who mentioned it. I realized later you meant R18 after re-reading the whole thread and checking the schematic. I picked up a 4.7K today to try. I tried to hookup at R25 but must have ruined the resistor removing the RTV as all I got was a bunch of noise. Put it back the way it was and still got a bunch of noise. So now I will be replacing R25. I do know how to calculate both resistors and capacitors in series and parallel. Had Basic Electronics 101 in route to BSME. I am not an expert when it comes to electronics and I don't have anything but a basic working knowledge of amps (4 books), a soldering iron and a multimeter. I have worked extensively on my BF Bandmaster and they sure are easier to work on than PCB amps and in particular the V5. It was bad in its original form. I went for the basic tube amp with a 18 watt vol/tone circuit in between the two triodes. Had it working fine until I tried to hookup at R25.:thwap: Thanks for your knowledge and especially the explanation of the cathode bias.
Sorry for how things are working for you on the amp. One thing to watch out for is that RTV getting into the solder joint when you go to resolder this could give you a cold solder joint problem. First place I worked at used humaseal on there PCBs in the high voltage section (portable ultrasonic flaw scope) and it was a pain to rework things. You should look to make sure the PCB traces and plated feedthrough are OK. If the circuit is open you will have no supply to the plates on the triodes. So I would buzz things out with an ohmmeter. I put a triode/pentode switch in the amps I have so just needed to solder to the lead of the resistor in the board. If you move the screen grid to the plus side of C16 you should use the stock value of 470 ohms for R18 sorry if that was not clear in post. A higher value may work but will probably cause degenerative feedback with the changing voltage on the screen grid (which may be OK?). That is why I posted the fact that the screen grid should be at C25 plus. If you check the daddy of this amp the VC508 you will see on that one they got it right.

[jim p]

Hi Jim,

Would it help to add a 22uf 450V filter cap (to ground) in the B+ supply where R18 was connected to J4?

I just happen to have several caps without amp "homes".

Thanks
No you would just be paralleling C15 the 47uf cap in that same circuit if the amp is quiet no real need. One area that looks like it could use decoupling is the plate load resistor of the first triode R5. I posted before how you can get sound through the amp with the volume control at minimum and think this is due to no separate decoupling on the triodes. So one thing you could do is put a 10k resistor between plus C17 and R5 then decouple the junction of the new 10k and R5 with the 22uf cap you have. I can draw a small section of the schematic if it would help to explain. If you look at a Bravehart amp schematic you will see that they have both triodes decoupled. Without the decoupling and with a tone stack between the triodes the signal feedthrough is not 180 degrees out of phase and will not be canceled. If you were going to use it to decouple the screen grid instead of moving R18 to C16 plus I would put a 10k in series with the 470 ohm R18 and decouple at the junction of the two resistors.

[schenkadere]

I bought one of these after I sold my perfectly modified Epiphone Valve Junior with the help of 18watt members and 300+ pages of chit-chat. I get bored rather easy, and was going to go with the Valve Junior again (I sold it to see if I could get the combo and do similar things, but the price increase told me that there were greener pastures) as a platform, but decided to try out the Crate V5 since it was a combo not much bigger than the VJ. I like 10 inch speakers, I liked the looks of the amp, and thought that even if I have to replace everything and even make up a tagboard for it, it would still be cool. I also was hearing what others have been saying about the Crate and when I got it, surprise! I agreed that there was something amiss and decided that to just accept it and give it back would be like throwing in the towel. I knew that it could be better and I systematically worked on each section to see how my $100 initial investment could be improved on.
Speaker was pulled first. Weighing about a pound and with a tiny magnet, tiny voice coil, stiff suspension and a plastic (!?) cone, I could tell just by tapping on it that this was a tone sucker and big part of the bass weakness. I figured that it could be used in an amplifier to take to the beach or other dirty, wet place. The chassis looked awfully close to the speaker magnet, and I didn't think I could get anything in there that would be decent.I measured the depth of other speakers that I had and found that I was wrong. There WAS room for a better speaker. I popped in a 50 watt Eminence 10 inch and it cleared the chassis. Hooked it up and fired it up- better tone and bass, but the amp was still shrill and unmusical.
Looking inside the amp on the circuitboard I saw of all horrors, an op amp!. OK, I know, you can get good sound out of op amps, but looking at the circuit with the volume control in the feedback loop in the second stage, was didn't sit right with me. After the op amp, the tube circuit was fairly conventional other than a quasi- parametric tone circuit between two tube sections of the 12AX7. But looking at the output of the second triode section, I could see that 90% of the signal was dumped just before it got to the grid of the power tube. I guess that is why they needed the op amp in there- to make up for lost gain in the output tube's voltage divider at the grid. (Why?)
So what I did is to cut some traces and add some jumpers to make it an all tube amp. After the input resistors (1.5Kohm and 1 Meg) I cut that trace going to the input of the op amp and sent it straight to the first tube grid and cut away any other parts that were there that might have influence. I decided that the tone control was not a bad thing, just different- and I left it as is. Since I now had a 250Kohm volume pot out of the circuit, I put that between the tone circuits and the grid to the second triode in place of the attenuation scheme that was there and to maintain grid to ground loading and control. I cut the traces around the volume pot and ran jumpers to the appropriate places (the pot connects to the output of the tone circuit, the two lower resistors were cut out, and the other end of the pot was run to ground. The wiper fed the second triode's grid.
I checked for stability (good) output power-6.1 watts at clipping; up to 9 watts fully overdriven. and residual noise 7mV rms (from the power supply). The tone control can be more easily understood when you use a fuzz pedal or other distortion box into the input. It changes the midrange tone in weird ways, but it is better than just a treble cut, since your guitar already has that. Put your metal pedal in front of it and see how much range of tones you can get from it.
Clean on this amp is very good. You can have your amp set at 12 noon, and your guitar all the way up and it will be clean until you start hitting notes hard (or if you have hotter pickups, perhaps a bit sooner. Alternately, you can turn the amp all the way up and still get clean tones with the guitar just cracked open and swell into the realm of output tube distortion. It is very easy on the ears and very pedal friendly. Using external EQ helps you get the tone that you need/want from various axes.
I had ordered a new transformer for this amp (EDCOR 15 watt- the same one I used in my Valve Junior with great success- $20.64 plus $6.37 shipping), but I am happy enough with it the way it is (the output transformer in the Crate is much bigger than the Valve Juniors'- 10 watts instead of 5). I get deep tone from only a 10 inch speaker and I have to be careful not to use the neck pickup too much- it rattles the pictures and things on the wall in the living room. That transformer is going to have to wait for my 6550 single-ended project. One big output tube- should be cool and about 10 watts!
If you just want to add lots of gain easily and just get your feet wet in trying things, pull out resistor R27 (10K) and short out R 15 (100K) and that will get all the lost voltage (the sound) to the output tube and not lost in those 2 resistors. That way you still have the 2-stage op amp pre driver and it might be more of what you want (if more is better- like metal tone). I wanted pure tube and I got it with only an Exacto knife, 3 pieces of short wire, and some cutters and soldering rig, I didn't need to replace the output transformer, or add any parts in any location. Other than replacing the speaker, that was my only expense. I got the 50 watt Eminence for $12.00 each when I bought 4 from a music outlet store on line. I have used those speakers in amps from this 5 watt one to a stereo 15 watt rig and for a 40 watt combo as well. Tubes are all stock. Surely a better transformer and/or tubes will make a difference, but I got night and day difference with these simple mods. Sounds great for little $$$. If you want, and you can pull the board and replace it yourself, I can mod it for anyone for $40.00 plus shipping (which would be nominal in a Priority mail flat rate envelope ($5.00). There is hope for Crate V5 to become the 'next big thing in small amps.

Deafelectromark (alias manoteal):rockon:

Curious what Eminence speaker you used that actually cleared the chassis? It's a tight squeeze in there.

I really love the cleans on this amp.

[timothymegg]

I changed the speaker to an Eminence Red Coat Ramrod 75w speaker. Sounds great and it cleared the chasis. The height of the speaker is 4.3"

[schenkadere]

I changed the speaker to an Eminence Red Coat Ramrod 75w speaker. Sounds great and it cleared the chasis. The height of the speaker is 4.3"

Weird...maybe the magnet shape is different. Mine is 4" high and it touches. I can't imagine all the specs and tolerances are exactly the same on these cheesy Chinese amps. Guess you got lucky and I didn't.:thwap:

Just looked that one up...it's like 70 bucks...I only paid 80 for the amp...my mind can't justify that. LOL.

[deafelectromark]

I used a 50 watt, 4 ohm Eminence that had a height of 3 1/2 inches, which is the same for most Fender Custom-made, 10" speakers. The original speaker is 3 3/4", so they both cleared easily. The actual opening depth before you hit the chassis is 4 1/4 inches. A friend wanted a Kustom, 50 watt, 8 ohm and 10 inch speaker and I decided to put it in my amp to see if it was clear. Well the speaker looks to be 4 1/4 measuring it out of the cab, and I popped it in and then bolted down the chassis screws and it felt like it WAS touching the chassis. But then I pushed down a little with my hands and found that the magnet was filling the gap due to it powerful magnet strength. I wedged in some credit cars to measure the gap and it came out to be 0.10 clearance (1/10th of an inch!) with 3 credit cards fitting in, and so I thought it was doable. So I pulled the amp out again and bolted the speaker to the proper torque, and put the amp back in again. But now the clearance was 0.20- twice as much. That was due to the speaker's cardboard mounting material being squished a bit by being bolted down.
There may be variations for this useful measurement, but I am convinced that any 10 inch speaker with a thickness of 4.05 to 4.15 will be able fit with at least 0.10 clearance between the amp chassis and speaker magnet. The Kustom sounds great and produces over 100dB with 5 watts input. Nice, no-shrilly tone and very good low extension, too.
I have two orders on the board mod I am doing to return it to a basically all-tube amp. I hope that their ears as as pleased as mine- I play this guy everyday and have no complaints. Wait and see their impressions after I send them back their modded boards.
Mark

I really love the cleans on this amp.[/QUOTE]

[schenkadere]

I used a 50 watt, 4 ohm Eminence that had a height of 3 1/2 inches, which is the same for most Fender Custom-made, 10" speakers. The original speaker is 3 3/4", so they both cleared easily. The actual opening depth before you hit the chassis is 4 1/4 inches. A friend wanted a Kustom, 50 watt, 8 ohm and 10 inch speaker and I decided to put it in my amp to see if it was clear. Well the speaker looks to be 4 1/4 measuring it out of the cab, and I popped it in and then bolted down the chassis screws and it felt like it WAS touching the chassis. But then I pushed down a little with my hands and found that the magnet was filling the gap due to it powerful magnet strength. I wedged in some credit cars to measure the gap and it came out to be 0.10 clearance (1/10th of an inch!) with 3 credit cards fitting in, and so I thought it was doable. So I pulled the amp out again and bolted the speaker to the proper torque, and put the amp back in again. But now the clearance was 0.20- twice as much. That was due to the speaker's cardboard mounting material being squished a bit by being bolted down.
There may be variations for this useful measurement, but I am convinced that any 10 inch speaker with a thickness of 4.05 to 4.15 will be able fit with at least 0.10 clearance between the amp chassis and speaker magnet. The Kustom sounds great and produces over 100dB with 5 watts input. Nice, no-shrilly tone and very good low extension, too.
I have two orders on the board mod I am doing to return it to a basically all-tube amp. I hope that their ears as as pleased as mine- I play this guy everyday and have no complaints. Wait and see their impressions after I send them back their modded boards.
Mark

I really love the cleans on this amp.[/QUOTE]

I used your post. I removed the chassis and pressed down hard on the speaker while tightening the screws down hard. Then(fighting the magnet)I repositioned the chassis and pulled it away from the speaker while tightening those screws. I did it...I got clearance...may only be .10" but it is definitely no longer touching and that speaker is definitely 4". My cabinet wouldn't take anything larger unless I opened the chassis screw holes larger. I'm happy because I really like the Warehouse speaker. It was a pain in the *** for sure...it's hard to be that firm and be careful at the same time, but I did it. No damage I can see...or hear...sounds great. Thanks for the post!:dude:

[jim p]

The first stage op amp is not a tube screamer it is an overdrive stage for the first triode. I have seen some postings for the V5 and its father the VC508 calling the first stage a tube screamer it is not. The VC508 has problems in that the op amp has only +/- 7 volt supplies while the V5 has +/- 15 volt supplies so you should not run into the rails (op amp clipping) with the V5. If you are worried about the supply limits R19 and R20 can be lowered in value to raise the rails to +/- 18 volts for more headroom. A tube screamer is an op amp with two diodes in the feedback to cause clipping which is a poor mans version of what a tube will do. Also the choice of op amp in a tube screamer is based on the op amp recovery time from clipping which should never occur in the V5. Changing the op amp in this amplifier to a JRC4558 would be a bad idea because its low input impedance will kill your highs from the guitar (plus the over all spec for the TL072 is better in noise and input impedance it is a fet op amp not a bipolar). The classic Ibanez tube screamer is a 250k load on your guitar while most of you tube types like the idea of 1 Meg to keep the highs. If you like the sound of a tube screamer fine but it is trying to simulate what an overdriven tube will do and you have a tube to overdrive so no reason to use it. If you want to overdrive a tube amp using an Ibanez tube screamer is not the way to do it, you want to up the signal level into the amplifier without clipping so the tube in the amp will clip.
Of course you need to get a volume control between the first and second triodes in the V5 to use the op amp as an overdrive if not it is just a volume control. So you will have a solid state preamp with tube output .

[jim p]

The easiest mod to do that I can think of is to keep the volume pot as a gain pot and convert the tone pot into a volume control. You will have no tone control on the amplifier but there are other amps sold that do not have a tone control. In another post I talked about the op amp as an overdrive so that should give you an idea of how things will work. There are no cuts in this mod and the pots do not need to be removed from the PCB (see that some people have had problems removing the pots). The tone pot will short or pass the signal from the first triode to the second relative to its resistance setting. The attached photos are of the marked up schematic and the PCB with orange arrows on the parts to be removed C4 is hard to see it is hiding on the right hand side of the tone pot.
1) Components that must be removed for mod C5 C6 C4 and R27

2) R13 I think should be removed you do not need the extra gain in op amp stages.

3) C24 should be removed and replaced for better bass with 47nf or for more bass change to 100nf

4) C26 should be removed for a flat signal output from amplifier it can be changed to 22nf for a bright output which may be better for overdrive if you save C6 you can parallel C26 with it to get 20nf (see other brightness mod in this post I would not do both)

5) Jumper from feedthrough (PCB hole) of C5 not connected to ground (right next to tone pot) to feedthrough (PCB hole) of R27 not connected to ground (hole connected to R15 by trace).

Note: Damage to pots can occur when you remove the knobs so take it easy and walk the knobs off do not just pry on one side protect the front panel with thin piece of wood and use a flat blade screwdriver against the bottom of the knob.

Note: That the resistor and capacitor leads have been bent outwards or inwards so heat the solder joint on the back side of PCB up and use soldering iron tip to straighten before you try to remove them. If not you may damage the plated hole the resistor or capacitor is attached to causing a break in the circuit on the PCB.

Note: The clear RTV (room temperature vulcanizing is what it stands for) can be removed with needle nose pliers and careful scraping (wood or fingernail) if it is still on the board and gets into your solder joint you may get a cold solder joint due to it so keep an eye out for it.
Note: In pictures you can see that the screen grid resistor has been attached where it should be at R16 R25 and C16+ junction

Other possible tweaks
For brightness remove C28 replace with 4.7nf (If you got C4 out in one piece you can put it here)
For more gain short out R15 with R15 as stock you get 0.316 of the signal at the plate of the first triode. With R15 shorted you get 0.362 of signal 14% more. If you want go crazy and short out R30 or R29 for more yet but if you used C28 for brightness need to make it 10nf insted of 4.7nf

If you want I can use a schematic capture program to make a schematic that may be clearer then attached photo.
If you see any error in this post or any others that I have done let me know do not want to misinform anyone (the web is good for that).
Thanks and Happy Motoring

[jim p]

For those of you that are into possible noise problems due to ground loops the PCB to chassis ground is in a bad location. If you look at the bottom of the PCB you will see that the PCB attaches to the chassis close to the front end of the amplifier (near guitar input). I have cut the traces around the mounting hole then moved this ground to the power supply side of the PCB by attaching the plated hole to the ground plane with solder and solder braid. Just need to scrape off solder mask on bottom of PCB with razor blade, tin the area with solder and bridge plane to plated hole. See attached photos of before and after.

[jim p]

It’s been posted that with the 10” speaker in a small box the output is boxey. Has any one used a Weber beam blocker to see what effect this would have on changing that?

[jim p]

Well rather then wait for an answer to my beam blocker question I tried a simple test of using a relish jar lid propped against the grill cloth to see how things sound. I like the result the highs are slightly muted and the sound a bit more off axis. It is an easy thing to try yourself to see what you think. (See attached photo)
So instead of buying a blocker have decided to do the arts and craft thing and make my own. Looking in the recycling bin decided to use the bottom of a Mountain Dew can with some prepunched pipe hanger I have. You have to be careful cutting up the soda can to not lacerate yourself, once it is installed in the amp children and small animals should be safe from its sharp edges. The inside bottom of the can is domed so it looks like the real thing. To keep the dome in place I filled the void in the back with some calk I already had open. I might paint the thing or just use a magic marker to make it black. And yes that speaker in the picture is the stock V5 speaker it also makes a neat refrigerator magnet.

[schenkadere]

Well rather then wait for an answer to my beam blocker question I tried a simple test of using a relish jar lid propped against the grill cloth to see how things sound. I like the result the highs are slightly muted and the sound a bit more off axis. It is an easy thing to try yourself to see what you think. (See attached photo)
So instead of buying a blocker have decided to do the arts and craft thing and make my own. Looking in the recycling bin decided to use the bottom of a Mountain Dew can with some prepunched pipe hanger I have. You have to be careful cutting up the soda can to not lacerate yourself, once it is installed in the amp children and small animals should be safe from its sharp edges. The inside bottom of the can is domed so it looks like the real thing. To keep the dome in place I filled the void in the back with some calk I already had open. I might paint the thing or just use a magic marker to make it black. And yes that speaker in the picture is the stock V5 speaker it also makes a neat refrigerator magnet.

The clearance between the chassis and the speaker magnet is so tight after doing a speaker replacement that I can't imagine being able to install the beam blocker and still keep the magnet off the metal of the chassis.

[jim p]

The clearance between the chassis and the speaker magnet is so tight after doing a speaker replacement that I can't imagine being able to install the beam blocker and still keep the magnet off the metal of the chassis.
I put in the post for "Changing the speaker on the V5" that maybe just a thin knit fabric might work to reduce the highs. Another way to go if the fabric doesn’t affect the sound much would be to attach the blocker to a piece of fabric stretched in front of the speaker inside of the cabinet. Last choice is to steal a Volvo grill and use that diagonal thing they have, not really but if the test works to give you the tone you want. Then be creative and try to think of a solution.

[jim p]

Has anyone out there tried feedback from the secondary of the output transformer to the cathode resistor of the second triode on this amplifier? I have tried an initial test where I needed to connect the red lead of the transformer to J4 and the brown lead to J5 to get the output in phase with the signal on R8. Then used a 100k resistor from the output to the cathode of the second triode but not sure of the over all tone because except for the screen resistor connection the amp is stock (not stock speaker). I am planning on making a head instead of a combo amp out of this one so was thinking of adding a presence control on it.
Note: I would not try this without a scope and signal generator because if the feedback is out of phase the amp may oscillate which might result in damage to amp. So use caution if you try this.

[schenkadere]

I put in the post for "Changing the speaker on the V5" that maybe just a thin knit fabric might work to reduce the highs. Another way to go if the fabric doesn’t affect the sound much would be to attach the blocker to a piece of fabric stretched in front of the speaker inside of the cabinet. Last choice is to steal a Volvo grill and use that diagonal thing they have, not really but if the test works to give you the tone you want. Then be creative and try to think of a solution.

Actually the Warehouse speaker doesn't give me any reason or need. I'm quite happy with my speaker choice.

[timothymegg]

Hi Guys,
I have just read all the comments on this thread, and it looks like many of you are finding that this amplifier is a sleeper and can sound good if a few things can be changed. I thought I would drop a line here and tell you my reaction to all the stuff that is suggested here.
First thing (almost always) the speaker must go.
Second thing is that adding more parts, or trying to make a 'booster box' in the amp with the 'provided' op-amp is more technical than most owners could do confidently.
...
When the op amp was removed, there was very little gain to play with. You can get output tube distortion if you play it hard, with hot pickups and perhaps your favorite stomp box. I feel that some of the best distortion comes from those little boxes on the floor. 2 tubes are not going to get you a lot of gain...
My pedal layout in guitar into a homemade tube distortion box with one 12AX7 in it, then a dbx 119 compressor/expander, and then to a Picoverb for lushness.
... just try this if you really want all-tube sound.
Begin by cutting the trace after the input jack leaving R10,R11 for input loading. This will be just before pin 3 of op amp. Run a short length of coax from there to pin 2 of the 12AX7, and ground this wire at only one end (to prevent ground loops).
You will be cutting the volume pot out of the circuit and reroute wires as follows-keep the tone control circuit for now).
Connect the middle wiper to pin 2 of 12AX7. Cut out the R7, 220K resistor and the pot will take it's place for the load and volume control BETWEEN the two 12AX7 halves (this is so your guitar and/or you stompbox can play clean into the preamp tube or to push it more into output stage distortion)
Connect the top of the control to the junction of R15, R29,and C28: and the bottom to ground. Cut out the 100K (R15) (or R27, 10K) Resistor(s) so that the second half of the preamp tube is driving the same load. So you are basically removing R15, R27 and R7. You can increase the gain by floating a highish value resistor between the grounded end of the volume control (or a 500K or more pot) which gives you more drive voltage out of the second stage of the preamp, but I left that the way it is because it does give me the balanced sound (clean and dirty) that I want.
Mark (manoteal at cox dot net)

Mark, I really like how simple your mod is compared to JP. I noticed you said that there is a lot less gain for distortion. Are you saying with just a standard strat/tele/les paul and a cable direct into the amp you get clean at max volume on both? If not, at what level do you start to get overdrive or distortion? And, with a simple overdrive pedal you are saying I can still get the distortion sounds? does it have to be a distortion pedal? (I have both, just trying to know before I mod the amp)

Also, the tone pot on the amp - JP stated that the op amp controls part of the tone control. So, cutting out the op amp - did you notice a difference on the tone pot and what is the difference?

Thank you for your time, skill, and experience!
Peace,
Timothy

[schenkadere]

Has anyone out there tried feedback from the secondary of the output transformer to the cathode resistor of the second triode on this amplifier? I have tried an initial test where I needed to connect the red lead of the transformer to J4 and the brown lead to J5 to get the output in phase with the signal on R8. Then used a 100k resistor from the output to the cathode of the second triode but not sure of the over all tone because except for the screen resistor connection the amp is stock (not stock speaker). I am planning on making a head instead of a combo amp out of this one so was thinking of adding a presence control on it.
Note: I would not try this without a scope and signal generator because if the feedback is out of phase the amp may oscillate which might result in damage to amp. So use caution if you try this.

I like the idea of making this amp a head...that would be very cool...talk about compact!

I actually find the stock tone control more useful than a standard single tone control...but that's just me.

I got quite a bit more headroom by swapping the power tube for a lower current EL84.

[Tomko]

Jim P- I'm still around trying to make something out of this cheap amp. I put a 4.7K on the screen grid and soldered it to R25 on the R26 side. I also put 280 ohm cathode bias resistor on EL84. My plate is still about 335v but the screen grid is about 294v. I also changed R25 to 7.9K. This dropped my voltage on the 12AX7 plates from 200v to 180v. Do you think I'm in the ballpark on the cathode bias on the EL84? Do you think 180v or 200v is better for the 12AX7? I also removed the 2.2 uf cathode bypass cap from the 2nd triode and replaced the 2.2 uf cathode bypass cap with a 25 uf on the first triode. I'm still not satisfied with the sound. It's clean up to 5 but not all that expresive but then really gets going about 6-7 with a lot of good distortion, not much inbetween. Plugged into a 1-12 extension cab by itself it really roars when turned up. I may try a 2nd non-original speaker. Have two around. What do you think? Anyone else want to chime in?

Buyer beware: My amp had a 2.2 uf cathode bias cap on both triodes of the 12AX7; not one 22 uf as shown on the schematic. 2.2 uf limits bass response to about 500 Hz with a 1500 resistor. Normal Fender design is 22-25 uf with 1500 ohm resistor and 100 k plate load resistor. This lowers response to about 40 Hz. Also standard input resistor is 68k. IMO the 1.5k is way too low. Take it for what it's worth. Comments?

[Tomko]

Jim
You are telling me I should be using the stock 470 ohm R18 screen grid resistor? I guess I wasn't clear on that. I had changed to a 1K and that seemed to work fine. I may have to use that value if I can't re-use or find a new 470 ohm 3+watt locally.
Thanks,
Tom

[jim p]

Jim
You are telling me I should be using the stock 470 ohm R18 screen grid resistor? I guess I wasn't clear on that. I had changed to a 1K and that seemed to work fine. I may have to use that value if I can't re-use or find a new 470 ohm 3+watt locally.
Thanks,
Tom
The value of R18 the screen grid resistor should be 470 ohms if you need to use a 1 K instead I think that will be fine. Moving the supply side of R18 to junction of R26 and R25 is the important thing to reduce the screen grid voltage. You should measure the voltage across the cathode resistor to calculate the plate current (cathode current minus approx. 4mA screen grid current) and multiply it times voltage across the tube (plate minus cathode voltage) to see if you are 12 watts or less. I don’t think having the cathode bypass value of 2.2uf is a problem that would give you a 3 db down at approx 50Hz. Old designs were into a factor of 10 greater then required. Also for the guitar 190Hz(My mistake lowest frequency is 82Hz)is suppose to be lowest frequency and having it at 2.2uf helps reduce 60Hz amplification (hum). The plate supply for the triodes should have dropped approx 20 volts with your value change to 7.9 k at R25 that should not be any real problem.

[jim p]

On the mods where the op amp is not used you should be able to use CW1 the volume pot with no cuts to the board. Just cut all the pins off the op amp and remove them from the board (or desolder and remove the op amp intact if you want). Then remove C25, C27 R2 R14 R28 R15 and R27. Then jumper what was pin 7 of the op amp to ground hole of R27. Replace R15 with a short or any value less then 1K ohms. Jumper op amp pin 6 to other side of R27 you can go twisted pair or coax if you want to the R27 connections. Now R27 is a variable resistor for volume control. Next jumper Pin 3 of the op amp to the junction of R2 and R1. This connects the ¼ inch input jack to the grid of the first triode.

For the tone stack at minimum remove C5 no mater where you set the tone pot this will cut the highs starting at 1.5 kHz. While C4 is odd it starts to cut the highs again as you are turning the tone pot up I would remove it it’s your choice.

Replace lost pre emphasis the op amp boosted the highs so with the tone stack you could go treble cut, flat or boosted. If you replace C1 the cathode bypass cap with a 200nf cap this will boost the highs starting at 500 Hz. From what I was reading about tube screamers this may work better for overdriving the amp also because will overdrive highs more then bass and should be less muddy.

SEE POST #168 FOR MORE DETAIL

Any errors here let me know thanks.

[timothymegg]

On the mods where the op amp is not used you should be able to use CW1 the volume pot with no cuts to the board. Just cut all the pins off the op amp and remove them from the board (or desolder and remove the op amp intact if you want). Then remove C25, C27 R2 R14 R28 R15 and R27. Then jumper what was pin 7 of the op amp to ground hole of R27. Replace R15 with a short or any value less then 1K ohms. Jumper op amp pin 6 to other side of R27 you can go twisted pair or coax if you want to the R27 connections. Now R27 is a variable resistor for volume control. Next jumper Pin 3 of the op amp to the junction of R2 and R1. This connects the ¼ inch input jack to the grid of the first triode.

For the tone stack at minimum remove C5 no mater where you set the tone pot this will cut the highs starting at 1.5 kHz. While C4 is odd it starts to cut the highs again as you are turning the tone pot up I would remove it it’s your choice.

Replace lost pre emphasis the op amp boosted the highs so with the tone stack you could go treble cut, flat or boosted. If you replace C1 the cathode bypass cap with a 200nf cap this will boost the highs starting at 500 Hz. From what I was reading about tube screamers this may work better for overdriving the amp also because will overdrive highs more then bass and should be less muddy.

Any errors here let me know thanks.

I like how you described the tone parts. This mod seems much simpler than your other mods! I'm still comparing this mod and deafelectromark's. I like the idea of not having to jumper the volume pot.

Jim_P - does the tone part of this mod work alongside deafelectro's mod?

Thanks,
Timothy

[schenkadere]

Hey guys...do you really feel this cheap little amp is worth all of this...or is it simply the challenge of doing it?

[Tomko]

schenkadere- probably not worth all the trouble I've put into it but there is something to the challenge of making a crappy $75 amp into a single ended all tube amp- if it sounds good! I allready had a couple extra speakers. Have you seen the price of a vintage Champ lately?

[goonrick]

I did my mods both for the challenge and to get a good sounding all-tube single-ended amp. I must say I'm pretty happy with the results. It was easier to do the mods than to build one from scratch and it costs way less.

[jim p]

I like how you described the tone parts. This mod seems much simpler than your other mods! I'm still comparing this mod and deafelectromark's. I like the idea of not having to jumper the volume pot.

Jim_P - does the tone part of this mod work alongside deafelectro's mod?

Thanks,
Timothy
I posted the mod because you do not have to cut any traces on the PCB this way and if you are not using the op amp just cut it out. So far none of the mods I have posted involve any cuts. The deafelectro mod makes no changes to the stock tone stack, what you want to do with the tone stack is up to you. As I have said the op amp provided a treble boost before the tone stack if you do not replace that some how the tone control will just be a treble cut. I posted another tone stack for all tube previously with a 220k resistor and a resistor and capacitor in parallel to add back in the boost. But changing the value of the cathode bypass capacitor to 200nf may be a better way to go if you plan on overdriving the input triode. Some people have put in the Lite II tone stack the only thing I can see about that that I don’t like is the tone control interacts with the volume control looks like you will need to increase the treble with volume to maintain the highs because the tone control is hooked to the volume pot wiper.
Another reason I posted this mod was that you do not have to remove the pots which some people are having a problem with. I have been taking parts out of PCBs for years so it is no problem for me. The op amp can just be removed by cutting off all its pins then just heat and remove them, me I have a desoldering tool and desolder each pin then remove the op amp in one piece and can use it elsewhere.

[SciHi]

I drew up an alternate tone control for Rock Mumbles based on "that" tone control. It has been used on VJ mods. Somewhat similar arrangement of caps and resistors but pot needs removed for this one also. Wrong resistor values on the first on, this one corrected:
http://i615.photobucket.com/albums/tt237/scihibmxer/v5tonestackmodcorrect.jpg

[schenkadere]

schenkadere- probably not worth all the trouble I've put into it but there is something to the challenge of making a crappy $75 amp into a single ended all tube amp- if it sounds good! I allready had a couple extra speakers. Have you seen the price of a vintage Champ lately?

Forget about vintage...look at the prices of any of the Fender amps...through the roof! Lucky I'm not a fan.

I'll be honest...I'm incredibly picky and consider myself an ultimate tone seeker on a budget and with the few simple mods I made on the V5 and the addition of a graphic eq in front, it has become one of the best clean amps I've ever owned. I'm pleasantly shocked. I couldn't be happier. I can't understand all the hate for this amp...what can one expect for a $79-99 tube amp...come on!

Good luck with your mods, guys....hope you achieve the tone you seek!:)

[jim p]

This is the no op amp modification with the op amp removed a continuation of post #160. How you get the op amp out of the board is up to you, basic way is to cut off all pins and remove them one at a time. Also can desolder all the pins and remove op amp in one piece.
Steps involved in modification after removing PCB from chassis

1) Remove op amp IC1, C25, R28, R14, C5, C4, R27, R15 and R2
2) Replace R15 with a jumper
3) Jumper from op amp pin 3 to junction of C25 R2 and R1 (amplifier input jumper)
4) Jumper from pin 7 of op amp to ground via of R27 (black wire in picture)
5) Jumper from op amp pin 6 to junction of R27, R15, R7 and pin2 (grid) of 12AX7 (orange wire in photo near volume pot)

Options:
Remove R7 for higher maximum signal on grid of second triode.
Short R30 or R29 and remove C28 for more maximum signal at grid of second triode.
Remove C27 and use the vias (plated holes) in the PCB to connect rheostat (pot) to location of R27. Makes for shorter jumper runs on PCB.
Replace loss of pre emphasis for tone stack by replacing C1 with a 200nf cap (voltage rating of 6 volts or greater) so tone control will be treble boost, flat and treble cut. Or instead change R9 to approx 220k and add a Resistor and capacitor in parallel with it for treble boost.

See attached pictures.
Picture of tools used to remove op amp, resistors and capacitors. Also to remove solder from PCB vias.
If you get a vacuum desoldetring tool best to use fresh solder to make better thermal contact with solder joint to be desoldered. Also allow enough time to heat joint before pulling the trigger on the desoldering tool count in your head 1001, 1002… for 10 to 20 sec. Remember ground plane connections and large component leads will require more time for good results. Keep in mind too much time will lift the copper trace from the PCB making for a rework job.
If you see any errors please let me know, thanks.

[deafelectromark]

Mark, I really like how simple your mod is compared to JP. I noticed you said that there is a lot less gain for distortion. Are you saying with just a standard strat/tele/les paul and a cable direct into the amp you get clean at max volume on both? If not, at what level do you start to get overdrive or distortion? And, with a simple overdrive pedal you are saying I can still get the distortion sounds? does it have to be a distortion pedal? (I have both, just trying to know before I mod the amp)

Also, the tone pot on the amp - JP stated that the op amp controls part of the tone control. So, cutting out the op amp - did you notice a difference on the tone pot and what is the difference?

Thank you for your time, skill, and experience!
Peace,
Timothy

HI Tim,
The amp in the stock form wastes 90% of the signal in the sound path. Since I remove the op-am, I simply 'get back' my gain from the 90% losses in the voltage divider. The tone stack is altered by the changes I make the circuitry, which alters impedance, loading and frequency response. I found this to be very slight compared to stock, so I left it as-is.
Guitar directly plugged in will give you a mostly clean sound up to half way, where is starts to crunch when you hit the strings harder or have high output pickups. All the way up and you are in full distortion and it is plenty loud as it is driving the output tube into saturation. So to answer your question- plugging straight in, get a reasonable volume approximately like a Fender Champ, or Gibson GA-5. Probably a bit louder.
Using pedals and outboard gear (fuzzes, compressor, EQ's, etc.) I only have the amp at the 9 o'clock position (1/4?). It is easily as loud as stock, so no worries there.
I have done a couple of mods for a couple of guys that have this amp and you should hear what they have to say about my mod. I charged them $40.00 plus shipping to do it and I have boards ready ahead of time since I now have two amps to compare each other to Stock and modded. I can get SPL measurements if you want for comparison, but my mod also reduces the hiss and noise dramatically.
Mark

[jim p]

The attached pictures are spice simulations of the tone stack at full treble with and without pre emphasis. R4 represents the output impedance of the first triode in the amplifier 100k plate load with 65k plate impedance in parallel plus 22k R9 in series at input to tone stack. R6 is the load of the volume control 220k plus 250k the value of this has little effect on frequency response curve. On the op amp the values are the same as in the V5 I set the pot in the feedback to a fixed value of 33k ohms. C1 and R2 are same as C26 and R28 in the amplifier and are the pre emphasis for tone control. I removed the capacitors in this simulation that are C5 (2.2nf) and C4 (4nf) in the V5 tone stack.
With pre emphasis there is a 10db gain from 200Hz to 3 kHz with the tone control at maximum that is shown in the screen capture of the simulation.
Without pre emphasis the frequency out is flat within a db from 200Hz to 5 kHz so no boost of the highs. So without putting pre emphasis back into the amplifier after you remove the op amp the tone control will just be a treble flat or cut without boost. You can replace boost by changing the value of the cathode bypass resistor of the first triode to a lower value approx 200nf. Or change R9 to a higher value of say 220k with a resistor and capacitor in parallel to cut the bass and boost the highs.
Sorry the images are so cropped but that is the size allowed for the post.
I can also run this simulation with spice model of the 12AX7 but the results should be similar to the ones shown.

[larryx]

:master: Hello gang, Just wanted to throw something out there for those of us who are electronics challenged (but actually guitar players!)I cannot begin to praise the MOD GOD (manoteal@cox.net) For 40 bucks plus a few dollars for shipping Mark cut though the technical blah! blah! blah! balonie and made my V5 amp sound better than I could have ever expected! This thing sounds as good or better than a friends modded Gipper GA5 and Fender Chimp and with ((no more irritating hiss!) Yes the annoying hiss is completely gone forever!! A miracle!!! With the help of a Marks expertise and a replacement speaker. I now have "ONE KICK *** LITTLE AMPLIFIER!!!!!!!! Now I'm sending Mark my whole family of V-series amps so he can work his magic on them as well!!So put your money where Marks bionic ears are and get him to mod your V series amp. This guy talks softly but carries the weight of the world of tonal bliss on his shoulders. Your "Tonal Bliss" is just a UPS sticker away!!So let Mark mod your Crate V-5 amp and then "JUST SHUT UP AND PLAY YOUR GUITARS !WILL YAH!!! THANK! YOU! MARK! (The Man o Steel) I mean (manoteal@cox.net):master: :bravo: :rotflmao: :D :beer: :AOK: :rockon: :dude:

[oldguy]

That's great news, Larry! 3 cheers for Mark, then. I've been following this thread for awhile, and it's very interesting and informative.

With over 170 posts in this thread, it would be nice if the new members (who haven't done so) introduce themselves in "TheFretPlayers" section.........there's some great info here, and other members who would benefit from meeting some of you new folks.;)
Thanks.

[larryx]

:AOK: Wow! I don't know what your use to playing through? I had a hard time getting anything that sounded even close to a guitar amplifier out of it! I have played through better sounding transistor radios! I mean the V5 pior to having (deafelectromark) mod it, was by far the worst sounding guitar amphs I have ever heard. Someone gave me an Estaban little P.O.S. amph that smoked the V5 (in its stock form!) The speaker was replaced right away with a Jensen MOD 10-35.But that made almost no difference in the sound of it! It wasn't until after deafelectromarks (manoteal@cox.net)modification did the amp come to life. And man did it! I sounds as good as an old Fender Tweed. Without any effects a or anything the amp sounds like a tube jewel from days past, only much quieter!!With my Korg AX1500 dialed into it with some eq and reverb it's delicious! I don't play through any of my higher wattage amphs anymore!It sounds that good!!Screaming Metal sounds,bluesy jazz sounds. It's all there! I took the stock speaker and tore the speaker cone out of it before pitching it in the gabage with a big. SEE YAH! .............Thank You Once Again Mark!!!!(manoteal@cox.net)is the solution to getting amazing sound out of this little hamster cage!!!!!!!!!!:AOK:

[msteeln]

...quite possibly the best they ever or will ever make, is the decade+ old Vintage Club 30. Notorious for sloppy wiring, repairs needed, etc., but even with stock componants, you'll be hard pressed to find a better 2X12 for rock/country/blues/alt, even the nastiest metal if you put a pedal in front. User reviews are usually glowing. As I've read in searches about this amp, a few simple tube mods and they can even improve, substantially.
It's my #1 match for my late 40s bakelite Rickenbacher 8 str. lap steel to get the great old spooky Hawaiian sound, but I got to dime every single knob, except vol., to saturate, which causes fits of repair.

And, they go dirt cheap...

[Spudman]

...quite possibly the best they ever or will ever make, is the decade+ old Vintage Club 30.
And, they go dirt cheap...

If you are talking the old blond ones then I'd love to find a VC30 dirt cheap. I've been looking for a while and it seems the word is out. I do still have my blond VC5212 and it does sound great.

I just realized I don't know anybody on this thread.:confused:

[msteeln]

If you are talking the old blond ones then I'd love to find a VC30 dirt cheap. I've been looking for a while and it seems the word is out. I do still have my blond VC5212 and it does sound great.Mine's the later(?) w/black tolex. It's due for a complete elec. overhaul and upgrade so it can hand against the abuse but not change the tones.
The 1X12s go even cheaper (duh...), but I can't imagine them sounding as good as the 2X12.

[deafelectromark]

Hello Mr. Moderators, sirs!
Thank you for membership. Lots of good guys with much overlap into other fields, and lots of opinions that make for genetic diversity.
I had a 2x8 inch speaker with old musical instrument Radio Shack speakers, and wouldn't you know it- it FRIED one of them with the V5. The bass is so strong that it tears cones and burns out voice coils- and this is with my amp setting at 9 o'clock (!?) I found another pair of 8's (I am using eights because it is the biggest thing that my wife will allow in the living room). I put the Crate on top and it looks mighty big for practice. You would be surprised at the bass in a sealed cabinet- even with only 8 inch speakers!
The speakers I replaced from Rat Shack are a pair of full range German high-fi speakers made by Dual. They are VERY sensitive (we're talking 95+ dB per watt). I decided to play it safe and maybe get a few more days out of them by doping the surrounds with black RTV silicone and small brush. You would think it would affect the tone, but having a 'rubber' and paper surround doesn't effect it much.(Maybe a bit less treble?)
All this from a 5 watt tube amp blowing up 20-30 watts of speakers? I am glad the Eminence in my combo is 50 watts, less bass that the 2X8 cabinet, but at least it won't fry. Beware the power of tubes in saturation!:confused:
What happened to the talk about the V5? Are we heading into another direction from the last few posts?
Mark

[schenkadere]

Hello Mr. Moderators, sirs!
Thank you for membership. Lots of good guys with much overlap into other fields, and lots of opinions that make for genetic diversity.
I had a 2x8 inch speaker with old musical instrument Radio Shack speakers, and wouldn't you know it- it FRIED one of them with the V5. The bass is so strong that it tears cones and burns out voice coils- and this is with my amp setting at 9 o'clock (!?) I found another pair of 8's (I am using eights because it is the biggest thing that my wife will allow in the living room). I put the Crate on top and it looks mighty big for practice. You would be surprised at the bass in a sealed cabinet- even with only 8 inch speakers!
The speakers I replaced from Rat Shack are a pair of full range German high-fi speakers made by Dual. They are VERY sensitive (we're talking 95+ dB per watt). I decided to play it safe and maybe get a few more days out of them by doping the surrounds with black RTV silicone and small brush. You would think it would affect the tone, but having a 'rubber' and paper surround doesn't effect it much.(Maybe a bit less treble?)
All this from a 5 watt tube amp blowing up 20-30 watts of speakers? I am glad the Eminence in my combo is 50 watts, less bass that the 2X8 cabinet, but at least it won't fry. Beware the power of tubes in saturation!:confused:
What happened to the talk about the V5? Are we heading into another direction from the last few posts?
Mark

So, do you do V5 mods for other than friends and family? What would be involved?

[larryx]

:master: :bravo: VC's are an awsome amphfffff!! I've had a VC50 for years. As well as my much loved BV60H. I also have modded /corrected versions of the entire V series MKll line. V-18 212,V-33 212,V-33H and now thanks to ((manoteal@cox.net))a modded and much loved V-5! The statement that you must have been refering to was directed at the V-5 in its stock form. And yes. In its stock form it was one of the worst sounding amplifiers that I have ever heard! SS or tube! So,no need to defend Crate. I still have some of their amps and love them. I own other brands such as Fender,Marshall,Vox.
I'm not partial to any of them. They all serve a purpose. And the Crate amps would fool anyone in a blind taste test. And the MKll's were a steal!! That's why I ended up with the family of them! Although I play the V-5 more than any of them! Now that it has been transformed into a smokin little amplifier!!
So stop wasting your time everyone. Stop reading these long winded posts regarding the V-5 mods. Just check in with deafelectromark((manoteal@cox.net)) And forget about all the turd polishers out there. He has the ((quick and easy)) solution to getting this amp sounding right. No techno voodoo about it!! Now who's got the big swingin technical#$%^. Can't read anymore crap ola about a 68 dollar amplifier. Enough already!!!!!!!:thwap::beer:

[larryx]

:thwap: :confused: :"OH MY GOD JIM! I'M A DOCTOR! NOT A DAMN GUITAR AMPH TECHNICIAN!"
"EASY THERE DR.McCOY.BONES"WE WILL JUST CALL ON MR.SCOTT" I THINK HE SAID SOMETHING ABOUT DILITHIUM CHRISTALS AND A 49 PICO FERAD CAPACITOR WILL TAKE US BACK TO WARP SPEED" ANY OF YOU ACTUAL GUITAR PLAYERS?THIS IS THE FRET. NOT THE CIRCUIT BOARD!:confused:

[jim p]

:thwap: :confused: :"OH MY GOD JIM! I'M A DOCTOR! NOT A DAMN GUITAR AMPH TECHNICIAN!"
"EASY THERE DR.McCOY.BONES"WE WILL JUST CALL ON MR.SCOTT" I THINK HE SAID SOMETHING ABOUT DILITHIUM CHRISTALS AND A 49 PICO FERAD CAPACITOR WILL TAKE US BACK TO WARP SPEED" ANY OF YOU ACTUAL GUITAR PLAYERS?THIS IS THE FRET. NOT THE CIRCUIT BOARD!:confused:
I am making these posts for people who want to do the mods themselves. If you can not fine that is your choice. Also some people want to know more about the things they use not just put the key in the car and drive. After all with an electric guitar a good portion of your sound is due to the amplifier. So I am looking at feedback from people who are making changes and what they think. Also ideas for other ways to mod the amp to get the tone they want. If you don’t need to know much about the things you use and want to be reliant on others for answers fine. Ignore my posts, if you care to know more read on and read more about amplifiers and there components here and elsewhere.

[SciHi]

...ideas for other ways to mod the amp to get the tone they want.

I would be interested in more details on your reverb mod/addition to the v5. Like a schematic, if possible. Thanks for sharing the technical detail for those of us still learning...

[tunghaichuan]

Larry,

Don't take this the wrong way, but this thread is for people who want to mod the V5. If you don't think it's worth modding and think it is a piece of crap, those are you're opinions and you're welcome to them. But no one says you have to read the "long winded" posts here. Jim P. has done a great job detailing mods to get the maximum out of the V5. There are plenty of other threads which could use your expertise.

tung



:master: :bravo: VC's are an awsome amphfffff!! I've had a VC50 for years. As well as my much loved BV60H. I also have modded /corrected versions of the entire V series MKll line. V-18 212,V-33 212,V-33H and now thanks to ((manoteal@cox.net))a modded and much loved V-5! The statement that you must have been refering to was directed at the V-5 in its stock form. And yes. In its stock form it was one of the worst sounding amplifiers that I have ever heard! SS or tube! So,no need to defend Crate. I still have some of their amps and love them. I own other brands such as Fender,Marshall,Vox.
I'm not partial to any of them. They all serve a purpose. And the Crate amps would fool anyone in a blind taste test. And the MKll's were a steal!! That's why I ended up with the family of them! Although I play the V-5 more than any of them! Now that it has been transformed into a smokin little amplifier!!
So stop wasting your time everyone. Stop reading these long winded posts regarding the V-5 mods. Just check in with deafelectromark((manoteal@cox.net)) And forget about all the turd polishers out there. He has the ((quick and easy)) solution to getting this amp sounding right. No techno voodoo about it!! Now who's got the big swingin technical#$%^. Can't read anymore crap ola about a 68 dollar amplifier. Enough already!!!!!!!:thwap::beer:

[tunghaichuan]

I am making these posts for people who want to do the mods themselves. If you can not fine that is your choice. Also some people want to know more about the things they use not just put the key in the car and drive. After all with an electric guitar a good portion of your sound is due to the amplifier. So I am looking at feedback from people who are making changes and what they think. Also ideas for other ways to mod the amp to get the tone they want. If you don’t need to know much about the things you use and want to be reliant on others for answers fine. Ignore my posts, if you care to know more read on and read more about amplifiers and there components here and elsewhere.

+1. Thanks for taking the time to detail your mods to the V5. I, for one, appreciate them.

tung

[goonrick]

I, for one, am glad this thread exists for the purpose of learning how to mod the V5. It is today's Tube 10, Valve Junior, et al which were the beginners modding platform for their times.

I bought mine with full intentions to mod it and I wouldn't have gotten anywhere near as good of results without the posts of Jim P. I personally don't mind seeing more and more ideas on how to mod this ugly little duckling (in stock form).

[larryx]

:confused: If you mod it then it would't be stock anymore?:confused:
Did you read my entire post? Or just a piece of it? I Love the little piece of crap.

:confused: ...................MODIFIED THAT IS?.............:confused:


Man you techno dweebs get uppity!

[larryx]

Wow Jim,
I had no idea that it's the amphhh that gives you a majority of your electric guitar sound? You know. I have been playing guitar through tube amplifiers for over 40 years. And I had no idea!:whatever: And I find it an insult to be talked to in such a condescending manner. Although I don't need to show off my electronic prowess in such a feeble format. You guys go back to modding your hamster cages now. I'm gonna go play of one my guitars. Through one of my collection of tube amphhhhs! :whatever:


<<<<<<<<<<SEEEYA! ...The Fret!!...Er THE CIRCUIT BOARD!>>>>>>

[deafelectromark]

So, do you do V5 mods for other than friends and family? What would be involved?
Hi Schenkadere,
Yes I mod boards for whomever just wants a pure tube amp- all I really do is bypass the op-amp and move the "volume control' out of the feedback loop (gain) of the op-amp and put it where it belongs- between the two tube halves so you can force the 1st section into distortion with your outboard pedals, and using the volume control to set the crunch going into the second stage. This gives you basically what most small, single-ended have in stock form. Then I just raise the gain lost by the voltage divider at the input of the second stage, to 'get back' the gain that is lost from the op-amp not being there.
I have told others in this list to just read my earlier postings (post #16 and on) about what is required and enough (I hope) information for tech-minded players to do themselves. I just offer my services for people that aren't comfortable messing with high voltage and circuit boards.
To really go at in in detail, JimP is the MOD GOD to me. :master: I am not fancy or technical. Just remove a few parts, add jumpers to the right places and Boom- an all-tube fun amp for practice. I will not make a name for myself doing this- it isn't rocket science and my ideas are not my own, but gleaned for the support of many, many others on the original (and massive) Epiphone Valve Junior thread on the 18WATT site. If you are capable of playing with tone stacks, op-amp mods and technical wizardry- this thread has plenty to get you on the path of making this little guy "your own amp".
I did my mod for myself and thought it was miles apart from what it sounded like stock. So I told people here that I would do it for them for $40.00 labor and postage. You could continue down the path on your own. What I did sounds right, even though the "Tone Control" is a bit funky. I just leave it straight up unless I need a bit up upper mid-range or treble cut.
Of course the first place to begin is with the speaker. Then you are moving in the right direction. I am glad that many here are sharing their ideas and knowledge about amps in general and this amp in particular.
Cheers!
Mark:rockon:

[jim p]

I'm still not satisfied with the sound. It's clean up to 5 but not all that expresive but then really gets going about 6-7 with a lot of good distortion, not much inbetween.
Sorry I am late on an answer to your question regarding the sound at higher volume settings vs. low volume setting. The only way to get that high volume distortion is at high volume, that is when the flyback of the output transformer and speaker create heavy third harmonic distortion. This is due to the collapsing magnetic field built up around the transformer and speaker with the output tube turning off. Wish I had a digital scope so I could attach a picture of what the plate voltage looks like in both cases. This voltage (counter emf) is what will possibly damage the transformer and or output tube if you run the amp with no load (speaker or resistor) or use a speaker with to high impedance for the amp.
If you want to get that sound at low volumes then you will need to use a hot plate, Weber microMass or I have seen posts where people are using L-pads for this. The L-pad is a dual pot that has one pot in series with the speaker (approx 8 ohms max for 8 ohm L-pad) and one in parallel with the speaker (approx 200 ohms max) that always looks like 8 ohms to the amplifier. As you reduce the volume to the speaker with the L-pad the series resistor increases and the parallel resistor decreases. This thread http://acapella.harmony-central.com/forums/showthread.php?p=20597125 shows how someone set up an L-pad up on a Crate VC508. You can also surf around and find how other people have done this mod. I saw one company Parts Express that sells these to those guys building mega watt kidney bleeding car stereo systems I would get a 50 or 100 watt model just to make sure it is sturdy, if it falls you will be running the amp with no load and that is not good.
The sound with the L-pad will not be the same as driving a speaker because it is a resistive load and will dampen the output unlike a speaker which is inductive. This is where the Weber microMass makes the most amount of sense for simulating the amp in overdrive because it is a speaker with no cone.
I suppose you could carve up the cone on the stock V5 speaker so it can not push any air and maybe use this as a basis for a load, but not sure that would be worth it if damage in sued.

PS: Looking out on the web a little more I would for sure go for a high watt model and see how hot it is getting when you use it. These are made to regulate the volume to a midrange speaker or tweeter so usually not dumping much power. Although we are talking about 5 watts so maybe I am being over cautious.
PPS: Did see a thread where a guy talked about an l-pad going up in smoke so go big if you do this.

[larryx]

:master: the humblest of oppologies to the gang. well shut my mouth.

over:beer:

[jim p]

I would be interested in more details on your reverb mod/addition to the v5. Like a schematic, if possible. Thanks for sharing the technical detail for those of us still learning...
Adding reverb to the V5 or Valve Jr. is not that hard to do relative to your skill level at bread boarding circuits. Not sure if any one has offered this modification in a kit level but a good chance if someone did it could be made to work in most of the EL84 amplifiers on the market now. With the Valve Jr. amplifiers I have they used the same transformer as the Epiphone Valve Special that had +/- 18 volt AC secondary they used for +/- 15 volt DC supplys for a DSP. Not sure why someone had the bright idea to run your main signal path through a DSP (analog to digital to analog?), looks like they don’t make the Special anymore I wonder why? I will probably do this mod in multiple posts, sure I will forget something and need to have a lot of attachments to illustrate the mod. The reverb tank that I think is the best choice is an Accutronics 8BB2A1B this is 190 ohm input, 2275 ohm output medium delay, input and output grounded, no lock and open side down. You can find the secret decoder table for reverb model numbers at Accutronics web site. They also have schematics for drive and recovery circuits that differ from the ones that I use. One problem with the 8BB2A1B is that the input is grounded, for the drive circuit I am using it needs to be isolated. So you will need to carefully drill out the rivets that hold the input RCA connector and remount the input connector PCB with nylon or rubber washers and screws with nuts to isolate it. No one has this tank in stock with an isolated input that I know of. As reverb tanks go the lower the input impedance the greater the operating frequency range, so using an 8 ohm tank would be great but that requires around a 1 watt audio amplifier to drive the reverb tank. Plus 190 ohm input should be good to approx 3 kHz which is about as far as the guitar is going to go anyway. The best price I have found for this tank is 22.95 at Antique Electronic Supply (www.tubesandmore.com) they have some neat t-shirts too, ok prices on tubes and capacitors. May as well look around and get what you may need to help offset the shipping and handling charge while you are there. Oh they did have some RCA cables real cheap in clearance and you will need one for this.
For the reverb driver circuit I suggest using the Texas Instruments TLE2072 or TLE2071 this is a fet input op amp with low output impedance and good output current capability it cost around 2.50 but splurge your worth it. I would not use the NE5532 because it has low input impedance and will load down the volume pot and change the input bandwidth, while the TL074 (a FET input) has low output current capability. About the drive circuit, in the schematic C1 is going to connect to the wiper of the volume pot you will need to add a 220k resistor in series with volume pot wiper to grid of second triode(will post marked up schematic in future). C1 and R1 are a high pass filter with 3db down at approx 330Hz, low frequency signals in the reverb tank will make it sound muddy so this blocks them. If you are all about control and want to have a dwell control (input level control) on the input to the reverb tank then use a 1 Meg log pot for R1 and connect its wiper to + input of op amp. R3 sets the current through the reverb tank you can play around with this value by plus and minus 50 ohms. Because the reverb input is the same as an inductor its input impedance will double per octave, 190 ohms at 1 kHz to 380 ohms at 2 kHz… ECT. R6 will limit the maximum impedance in the op amp feed back path so the op amp will not get pasted into a supply rail.
I have attached pictures of the Accutronics and Ruby reverb tanks the case of the Ruby is nicer looking then the Accutronics and has nylon vibration isolation bushings standard. The Ruby tank also has small PCB inputs that have jumpers to make or break the isolation of the inputs and outputs. While I like the guts of the Accutronics better its more old school with the brass and solder connecting the magnets attached to the springs. The Ruby is the stock OEM tank from a Crate V50 that I will upgrade to a long tank.
That is it for now if you are ordering parts you may want to wait to see the reverb recovery circuit first that I will post soon. By the way if you kept the stock op amp in one piece you will be able to use it for the recovery amplifier. Also if you can figure things out for yourself as far as op amps you could buffer an NE5532 with one of the TL072 op amps so you can use that as a reverb driver then use the other half of the TL072 as the recovery amplifier.
All for now more to follow.

PS: If you are adding reverb check post #364 there I changed the reverb recovery circuit to a differential amplifier and used a jfet buffer in the tank on the reverb output. If you stay with the reverb recovery circuit in these posts you should isolate both the input and output RCA jacks and run a separate ground wire to the reverb tank chassis for lower noise. Also can’t hurt to put metal tape or a metal plate under the reverb tank to help reduce noise the plate or tape needs to be grounded also.

[jim p]

Previously on Modding the V5. In the previous post I covered the reverb tank driver circuit, now for the recovery amplifier. Here is where you get to use that TL072 op amp if you still have it in one piece. Looking at the attached schematic of the reverb recovery circuit I have made a change from most recovery circuits by adding C2 as a high pass filter. Because on the V5 that I have added reverb to, before adding reverb I had no 60 Hz hum at all (That 1 Hennery choke in the plate supply does wonders) now I have some with high levels of reverb (space the final frontier levels). As noted on the schematic a value of 100nF maybe better at blocking the 60 Hz hum. Moving on to the feed back loop of the op amp C1, R2, R3 and C3 the value of C1 keeps the op amp at unity gain at DC with a 3db down point at 140Hz this maybe another capacitor you could lower to reduce hum by changing to 220nf. If you know op amps you can see that you have plenty of gain (R3/R2 +1) approx 43 times the signal from the reverb tank. Across the feed back resistor R3 is C3 this will roll off the maximum output frequency of the amplifier at approx 4 kHz which will help prevent the possibility of oscillation of the op amp (also limit of reverb tank bandwidth). The output of the amplifier is coupled to the output level control through C4 by my calculation you maybe able to use a value of 220nf instead if you wish. Also if you added a resistor in series with the pot you could set a limit on maximum reverb level if you want. The wiper of the reverb level pot is going to be connected to R7 (220k ohms) on the Crate V5 PCB. The grounded side of R7 needs to be removed from the PCB and connected to the pot so R7 will be connected to the grid of the tube on one side and the reverb pot on the other. In the previous post I stated you need to add a 220k resistor from the wiper of the volume pot to the grid of the tube, this will sum the clean signal and the reverb signal at the grid of the tube. You will also need to add a 100 to 330pf cap from the grid of the tube to ground to help reduce or prevent reverb feedback. This mod keeps the clean signal path pure tube so you are stuck with the possibility of reverb feedback at high reverb level settings. If an op amp was used to buffer the output of the volume pot it would prevent this (you could use a cathode follower tube ckt also but). Or if an op amp was used as a summing amplifier for the clean and reverb signal this would also prevent the possibility of feedback. But the feedback will let you know the reverb is working so just consider it a test signal or you can use it to get peoples attention. One detail that is not on the schematics is decoupling of the power supplies on the bread boards I have 22-50 ohms in series with the +/- supplies with 22uf tant to ground. I took the supplies from C12+ and C13- to get approx 18 volts. If you have removed IC1 the op amp in the PCB you could reduce R19 and R20 to get +/- 18 volts at C10+ and C11- (you will need to have this circuit wired in and working to determine the value needed). I wanted greater then +/- 15 volts for maximum headroom for the op amps by there spec you could go as high as +/- 19 volts. Also I did not decouple the driver amplifier and recovery amplifier separately if you want to go for it. I would put decoupling on your proto board though because it will be located a distance from the power supply.
Next stuff to cover is hard wiring the RCA cables or installing female RCA Oh! Not politically correct sorry my bad, I meant RCA receptacles on the chassis. How to mount the reverb tank in the cabinet. How you mount the proto board is up to you.
Anyway see attachments.
Also in previous post you can see 9 volt battery clips on the proto board, I used two half dead 9 volt batterys to test the op amps before installing the board. I have a scope and signal generator to work with if you only have a meter I have to think of what you could do to test the board first.Maybe we can use the guitar as a signal generator and look for AC volts at the output of the op amp on both circuits. After an initial DC test of the circuit.
Any mistakes here please let me know,thanks.

[jim p]

Now that you built the reverb drive and recovery circuit how do you test it? What I have done is to attach two 9 volt battery clips for the +/- 18 volt supplies for DC and signal tests. So attach the clips and plug in the batteries hope you have decoupling resistors in series you can use them to check the supply current. On the board I built with one TL072 and one TLE2071 the positive and negative supply current was approx 8mA on each supply. So you can measure the voltage drop across the decoupling resistor divide it by the resistor value to calculate the supply current. If you have from 6 to 18mA per supply you are doing good so far. Next measure the voltage at the output pin of both amplifiers (pin 6 on single op amp, pin 1 or 7 on a dual) there voltage should be approx 0 volts with no signal.
Now for the signal test. Disconnect both batteries. What I did was to attach a ¼” jack to use a guitar as the input signal. You attach the jack at the same point where you will connect the volume pot to the reverb driver amplifier. Next connect the reverb driver amplifier output to the input of the reverb recovery amplifier. You will now need a cheep little high impedance speaker, old earphone, transistor radio speaker, alarm clock radio speaker whatever you have or can find. With a large value non polar capacitor 10uf or greater (you can make a non polar capacitor by connecting two polar capacitors plus to plus or minus to minus that will be equal to half there value) in series connect the speaker to the output of the reverb driver amplifier. Plug the guitar into the input connect the two batteries strum the guitar and listen. It might sound crummy but if you hear it you are good so far. Next unplug the batteries and move speaker connection to output of recovery amplifier. Reconnect the batteries and play away, sound coming out good you are all set to stick this puppy in the amplifier. If any of these tests fail look around for bad connections get your ohmmeter out and start seeing where things went wrong.

Regarding the supply rails to the amplifier circuit having less then 18 volts is probably OK. I have been calculating the maximum peak voltage required to drive the reverb tank and that looks to be approx 10 volts peak at 4 kHz so +/- 15 volts should be fine.
See the attached picture and schematic

[jim p]

On to the reverb tank. As I said in the previous post you will need to isolate the input to the reverb tank. I have done this by using a drill bit and routing out the rivets by hand not using a power tool. I also used a pair of diagonals to cut away the rivets. The reverb tank is not meant to take a lot of abuse so I think a power tool would be risky. In my case I have removed the spring assembly first because I am swapping the guts of the Accutronics with the Ruby tank. I am going to make a head amp out of the third Crate V5 so the reverb tank will be visible and the Ruby looks nice on the outside. After you get the input RCA connector free from the reverb chassis you will need to put insulation between it and the chassis then reattach it with screws and nuts. I used nylon washers for insulation and nylocks for the nuts. Nylocks are the nuts with a cinched in unthreaded nylon washer attached so they will not fall off due to vibration or failure to tighten completely. These are great to use on an amplifier so you do not need to worry about a loose nut floating around shorting out the amplifier. If you do not use nylocks I would use some loctite, nail polish or paint on the nuts to prevent them from coming loose.

Mounting the reverb tank in the amplifier. To do this I used 8-32 x 1 ½” hanger bolts, mounting the tank on the bottom of the amplifier cabinet. Hanger bolts are wood screws on one end and machine threads on the other. You will probably need to remove the speaker and possibly the baffle board to get easy access to mount the tank. Also will need to remove the lower back panel and using a flat blade screwdriver and pliers remove Velcro straps on bottom of cabinet (remove speaker first to avoid damage). To locate the placement of the four holes set the reverb tank on the inside bottom of the amplifier, place it in a location that will clear the speaker and allow for the connection of the RCA cables. Then mark the center of the four holes on the outside corners of the reverb tank. Next drill a small pilot hole be careful to not drill through to outside of the cabinet if in doubt put a piece of masking tape on the drill bit as a guide for the hole depth. You will need two nuts on each screw to lock them against each other for both installation of the screws into the cabinet and to hold the reverb tank. Screw the hanger bolts into the bottom of the cabinet again be careful to not go so far as to break through to the outside of the cabinet. Now you will need washers, nuts and springs, rubber or foam to mount the tank so it is isolated from the cabinet. This is to reduce pickup of the sound from the speaker which will muddy the sound produced by the reverb tank. In the attached picture you can see that I used springs for this. Use two nuts on each screw to lock them together but allow for free movement of the reverb tank.
Note one thing that may work to suspend the reverb tank is to cut up and use the foam that is packed into the reverb tank to protect it for shipping. Also you could use a bag to mount the tank but unless it is padded I don’t think it will isolate the tank from vibration.
PS If you have a fear of routing out the rivets on the tank I suggested as a second choice the 8DB2C1B tank. This is a 310 ohm input, isolated input tank the input current requirement is approx the same but you will loose bandwidth vs the 8BB2A1B

[SciHi]

Adding reverb to the V5 or Valve Jr. is not that hard to do...

Thanks Jim, I have a selection of opamps and project board to build one. I will let you know how it turns out.

SciHi

[jim p]

Last thing is where to put the proto board and the reverb level control. I have installed the proto board on the input jack side of the main PCB. I used the two screws that hold the PCB to connect brackets that I have standoffs attached to that hold the reverb amplifiers. Another way to go would be long metric screws with pass-through standoffs (a cut up Bic pen cylinder) to hold the reverb amp board. I have mounted the reverb level pot on the back of the chassis next to the speaker jack. I did not want to mess with front panel. But if you move the power indicator to above the power switch. The spacing is about right for putting the level control where the power indicator was. (See picture) So if you get a pot and knob from Crate it will look almost stock. Crate has a 20k audio pot in there tone stacks on V18, V33 and V50 or change to different knobs that match.
Guess I am leaving out mounting of RCA cable to PCB. I just hardwired to the board and ran the cable out a ventilation slot on the chassis. Mounting a dual RCA receptacle would be the best but I am not that crafty.

[flyk35r]

Thanks for the directions Jim. I managed to make your first mods without screwing the thing up.

Gary

[Tomko]

Thanks Jim, I'm still messing around and messing things up. I get it going good then I try to improve it and then back to the drawing- uh I mean circuit board. I'll try to keep this short as possible as I read it is a guitar player (which I am) thread and not a PCB modification thread but we electric players do need amps so the neighbors can hear us. I think the major problem with this amp- other than the obvious- is the power supply puts about 330 volts on my EL84 plate. The tube is designed to handle 300 volts max. I found a way to rectify this but my screen grid was then way more than my plate voltage. So then I went to lowering my screen grid and on and on....Going to the hospital so I'll have a couple weeks of recovery to again rectify the current problem. We have one electronics store in this one horse town other than radio shack so I have problems getting resistors that fit those tiny holes with the correct ratings. What I really want is more good clean headroom. Is that more than I can ask from a 5 watt single ended amp? Wish it had a tube rectifier:rotflmao: See you guys in a couple weeks.

[jim p]

Thanks for the directions Jim. I managed to make your first mods without screwing the thing up.

Gary
thanks for the feedback glad things are working for you.

[jim p]

I don't think the plate voltage being on the high side is a problem as long as the plate current is low enough to keep the plate at 12 watts. When the output tube goes positive there is better then 400 volts on the plate from transformer flyback. If you want to see a tube out of speck go to the Fender site and open the schematic for the Champ 600 they have 14 watts on a 12 watt tube and screen grid at 360 volts, should be 285 volts or less.

[jim p]

Another modification you can add to the V5 is a presence control which is adjustable negative feedback. Not sure why I have to state negative feedback because positive feedback would turn the amplifier into an oscillator. What I have done is to remove C8 the cathode bypass capacitor on the second triode and put a 10k pot with 22uf in series in parallel with R8. Then I found I needed to reverse the wires to the ¼ inch output jack to the speaker so orange to ground and black to the tip of the ¼ inch jack. You should also check that the J4 connection is a brown wire while J5 should be a red wire. Then from the black wire to the speaker jack I connected a 57k ¼ watt resistor to the cathode of the second triode. I wired the pot as a rheostat so maximum resistance is full clockwise equal to full feedback. Then if you dial the pot full counter clockwise the 22uf is in parallel with R8 and as the amp is stock you have no feedback.
What feedback will do is when the output tube is shutting down its control grid is going negative then its plate supply, the transformer inductance and speaker inductance is taking the output tube plate positive (flyback). If it goes more positive then it should relative to the input at the grid of the second triode the triode will shut off turning the output tube on pulling the plate voltage down. So with feedback there will be less distortion in the output signal. Almost all Fender amplifiers the Champ included have negative feedback. With feedback you will notice a loss in gain relative to the volume pot setting without feedback. Also the amplifier may not sound as bright, the brightness due to harmonic distortion that will be reduced by feedback.
A quick way to try out feedback without mounting the pot someplace would be to just remove C8 and install the 57k feedback resistor from the transformer secondary to the cathode of the second triode and see how you like it.
On the positive feedback front I never did it to see how bad that would be because if you do it wrong that is what you will have. What should happen is a constant screech or motor boating sound coming from the amplifier. If you do the whole mod with a pot you can set to the no feedback position then slowly dial in feedback if everything is right no odd noises.
See attached schematic and pictures.
Let me know of any errors, thanks

I am going to post scope pictures of what the output signal looks like with and without feedback. Also with resistor load vs. speaker as a load.

[jim p]

Instead of having a rectifier tube for plate voltage sag you can just use a watt wasting resistor in the plate supply. For someone that wants that old time amplifier supply voltage sag they would get because the amplifier had a rectifier tube the cheep and switchable solution is to use a 500 ohm 3 watt to 1k ohm 5 watt in series with the plate supply voltage on the V5 with a low value cap after it say 10uf 450 volts on the output side of the choke. If you add a switch across this resistor you now have both sag and new world diode rectifier no sag settings. This is a feature that Mesa Boogie has on some of there amplifiers go to the Schematic Heaven web site and check through the schematics there to see.

Another way to go would be to put the resistor on the input side of the choke so between the rectifier bridge and the first filter cap C14 and bleeder resistor R24. Now that I think about it this would be a better simulation on having a tube rectifier. There use a 54 ohm 5 watt to a 120 ohm 5 watt resistor. When you look at tube rectifier data sheets they need to have a choke on there output in some cases because the high instantaneous current of having a capacitor on there output would have fried them. Another plus factor of tube rectifiers was there lag on power up allows the filament supplies to heat up the tubes before the plate supply comes up, so this was like a built in standby switch on power up with less stress on the components. The down side is there resistance causes the power supply to sag with a change in load but maybe that is the sound you are after.

Note to increase the rate of the sag lowering the value of capacitor C14 (47uf) may be required say drop it down to a 10uf instead. So you could swap C17 and C14 to try this out.

On looking into this more using spice simulation and the curves on the data sheet for a 5Y3GT data sheet the thing to go with is 50 ohms in series with the bridge rectifier. The voltage drop across the rectifier tube looks to be a constant and the drop on the curves from 50 mA to 120 mA is approx equal to the 50 ohms that the rectifier tube requires when used without a choke. On simulation the supply has a gentle slope when a current transient (sudden jump from 50 mA to 120mA) is applied this also limits current on the filter cap which makes its life easer. On a single ended amplifier like this one a transient on the plate supply will appear at the output so this maybe a mod worth considering.

I have posted a picture of the sag mod and a marked up schematic showing the mod. This mod has dropped the plate supply down to 310 volts and when the amp is driven hard it drops another 15 volts. You will need to remove the pcb to get the diodes out of the board the leads are bent over on the solder side and need to be straightened before removal.

[jim p]

On the post for changing the speaker on the Crate it was pointed out to me that I was wrong on the lowest frequency from a guitar. I looked around and sure enough it is 82Hz not 190Hz. So I am going to go through my old posts and correct any error and any component values that may need to be changed regarding this. Thanks, I wish I knew this sooner. Also may update this post with the number of the posts affected.

I went through and changed post numbers #23, #26 and #32 for componet value errors I think it was the value of C24 to 100nF in all cases, thanks.

[timothymegg]

I looked the mod deafelectromark (manoteal) posted with the schematic and, I think there is a discrepancy? In post 16 talk about the jumper from before the op amp to the first triode stage. In post #97 the actual pin number of the jumper is mentioned as pin 2. Looking at the schematic, if it was jumped to pin 2 then there would be nothing connected to pin 7 of the preamp tube. My guess is that the actual connection should be to pin 7? There is also mention of grounding one end of the coax... is that just the shielding or the core too?

I have no electrical experience so I am asking the people who are in the know to help on this one. :D Timothy

PS: below is deafelectromark's posts that apply here. I have also tried to link the schematic with my best guess of the mod.



Post #16
After the input resistors (1.5Kohm and 1 Meg) I cut that trace going to the input of the op amp and sent it straight to the first tube grid and cut away any other parts that were there that might have influence. Since I now had a 250Kohm volume pot out of the circuit, I put that between the tone circuits and the grid to the second triode in place of the attenuation scheme that was there and to maintain grid to ground loading and control. I cut the traces around the volume pot and ran jumpers to the appropriate places (the pot connects to the output of the tone circuit, the two lower resistors were cut out, and the other end of the pot was run to ground. The wiper fed the second triode's grid.
Deafelectromark (alias manoteal):rockon:

Post #97
Begin by cutting the trace after the input jack leaving R10,R11 for input loading. This will be just before pin 3 of op amp. Run a short length of coax from there to pin 2 of the 12AX7, and ground this wire at only one end (to prevent ground loops).
You will be cutting the volume pot out of the circuit and reroute wires as follows-keep the tone control circuit for now).
Connect the middle wiper to pin 2 of 12AX7. Cut out the R7, 220K resistor and the pot will take it's place for the load and volume control BETWEEN the two 12AX7 halves (this is so your guitar and/or you stompbox can play clean into the preamp tube or to push it more into output stage distortion)
Connect the top of the control to the junction of R15, R29,and C28: and the bottom to ground. Cut out the 100K (R15) (or R27, 10K) Resistor(s) so that the second half of the preamp tube is driving the same load. So you are basically removing R15, R27 and R7.

http://i29.photobucket.com/albums/c257/t_achin/guitar/v5schmaticmod.jpg

http://i29.photobucket.com/albums/c257/t_achin/guitar/v5schmaticboardmod.jpg

[deafelectromark]

[QUOTE=timothymegg]I looked the mod deafelectromark (manoteal) posted with the schematic and, I think there is a discrepancy? In post 16 talk about the jumper from before the op amp to the first triode stage. In post #97 the actual pin number of the jumper is mentioned as pin 2. Looking at the schematic, if it was jumped to pin 2 then there would be nothing connected to pin 7 of the preamp tube. My guess is that the actual connection should be to pin 7? There is also mention of grounding one end of the coax... is that just the shielding or the core too?

I have no electrical experience so I am asking the people who are in the know to help on this one. :D Timothy

PS: below is deafelectromark's posts that apply here. I have also tried to link the schematic with my best guess of the mod.

You are right. :thwap: The second half of the preamp tube's input is pin 2 on the schematic and not pin 7. Pin 7 is the input to the first half of the triode (from the guitar jack and as shown in the schematic). I will have to pull my board and look at it again to see what I did. Sometimes I think that lower numbers come first (hence the confusion about pin 2 and 7) Remember that tubes pins are clockwise from the bottom after the space and not from the top- I made this transcription error late at night and pretty groggy. My apologies to all that have tried this and it didn't work for them.
I will double check my work (three happy customers right now for the boards that I made for them), so I just made a mistake in that post. I will post again with the right information.
In reference to shielded wire (coax), the coax is not really needed (I didn't have problems with it or without it- it is such a short run) but if you do use coax only ground one end of it (I prefer the input side coming from the input jack ground) for reduced ground loop problems. The middle conductor (not the braid, is for running a connection past the opamp to the input pin of the tube's first section (pin 7). It is always the braided part that is connected to ground (at only one end).
Does that make sense?:confused:

Thanks for catching that Timothy. I was just seeing if anyone was awake! :bravo:

Mark

[SciHi]

I have also tried to link the schematic with my best guess of the mod.

I haven't done the v5 mod, but I think you want to either cut the trace after R11 before the diodes, or pull R10 leg and move R11 up front where it should be and connect from R10 leg to the tube input. If you pull R1, then you would just run the jumper to the tube side R1 hole. (maybe these pictures will work? WOW, guess I got carried away in making them small, maybe better now...)

http://i615.photobucket.com/albums/tt237/scihibmxer/v5inputopampbypass.jpg

http://i615.photobucket.com/albums/tt237/scihibmxer/v5inputreturn.jpg

[timothymegg]

Ok, I got some pictures of deafelectromark's mod and so, I think I finally have it how he did the mod on the schematic and his pictures of the board.

http://i29.photobucket.com/albums/c257/t_achin/guitar/TopofV5.jpg
http://i29.photobucket.com/albums/c257/t_achin/guitar/V5othersidewithquestionsanddrawninw.jpg
http://i29.photobucket.com/albums/c257/t_achin/guitar/v5schmaticmodv23.jpg

[timothymegg]

pull R10 leg and move R11 up front where it should be
I'm curious why R11 should be upfront? What does that do? and what does having the way it is change anything?

[jim p]

Caution the schematic mark up of the volume pot in post #207 is wrong. Where it shows the red wire connected on the pot should be where the pot should be grounded. Then the red wire should be connected on the side of the pot that used to be connected to pin 7 of the op amp. The little dot on the schematic symbol is probably indication of clock wise direction so at full clock wise you want the wiper of the pot at the R29 side(when mod completed). There is also a cut not shown on the schematic the wiper needs to be cut free from the other terminal of the pot. If you leave R1 in this will give you some feedback for high frequencies on the input triode and if over driving the input to amp sounded shrill it would give a plate to grid feedback cap something to work against. The diodes are a few Pico farads the guitar cable is more capacitance then they are so no big need to remove them they were in there to protect the op amp input so your choice. The location of the 1 Meg to ground is not that critical the difference in distance is what an inch or so this is inside of a shielded enclosure and these are audio frequencies. If you remove the op amp C25 and R2 all you need to do is run a jumper from the feedthrough hole of pin 3 of the op amp to feedthrough hole of C25 or R2 to connect input signal to first stage.

[Rampant]

Hello guys
I'm new around here and have just found this thread.
Although I'm in UK, I bought this V5 while in the USA for work a couple of months ago. A bargain, I thought and I still think it sounds pretty good for the money and way better than my YamGA15 (first amp - in deal with guitar).

I've got a new Jensen speaker arriving for it soon and I've already replaced the tubes - oh yeah, Ive substituted the 12ax7 for a 12at7.

I'm interested in modding, but have never done anything like this before. I'd like a little more bass response if anything - please would you collectively suggest what I could do?

Cheerz

Mark H

[jim p]

First off I would get a clean copy of the schematic either from a post or Crate. Then go through all the posts here that should give you an idea of what is going on in and with the amplifier. As stated way back this amp by design is a solid state preamp (op amp) with a tube output so not ideal. Also it is based off an amp that had an 8 inch speaker that they limited the bass response on. Most of the parts on the amplifier are good except the speaker, screws and nuts. You have a double sided PCB with plated holes I was just looking inside a Epiphone Valve Jr. that has your chepo single sided no plated holes PCB. You also get that 1 Hennery choke in the power supply, iron being a big expense to a manufacture in cost and shipping weight. So anyway go through the posts and figure what mod makes the most sense for you in terms of skill level and the tone you want. For the most bass response adding feedback will extend bass by lowering output impedance therefore reflected impedance at the primary. Also the triode mode will increase bass response by lowering the tube impedance to 2 K ohms from the pentode mode impedance of 35 to 50 k ohms but with loss of output power 1.5 watts and darker sound.

[timothymegg]

Caution the schematic mark up of the volume pot in post #207 is wrong. Where it shows the red wire connected on the pot should be where the pot should be grounded. Then the red wire should be connected on the side of the pot that used to be connected to pin 7 of the op amp. The little dot on the schematic symbol is probably indication of clock wise direction so at full clock wise you want the wiper of the pot at the R29 side(when mod completed). There is also a cut not shown on the schematic the wiper needs to be cut free from the other terminal of the pot. If you leave R1 in this will give you some feedback for high frequencies on the input triode and if over driving the input to amp sounded shrill it would give a plate to grid feedback cap something to work against. The diodes are a few Pico farads the guitar cable is more capacitance then they are so no big need to remove them they were in there to protect the op amp input so your choice. The location of the 1 Meg to ground is not that critical the difference in distance is what an inch or so this is inside of a shielded enclosure and these are audio frequencies. If you remove the op amp C25 and R2 all you need to do is run a jumper from the feedthrough hole of pin 3 of the op amp to feedthrough hole of C25 or R2 to connect input signal to first stage.

I am no expert. I appreciate all that you do to help me figure this stuff out. Thanks Jim P. After I looked at the pictures supplied by deafelectromark after his mod I checked and rechecked where he hooked up the jumpers that he used. I don't think I missed anything and, I drew it the way he jumped it from the photos and his description. So, I have looked at it again after you said what you did - I still think that I have it correct. (Ill give you the trace cut between the wiper and the right side of CW1-1). The idea to leave in R1 and jump from Pin 3 to C25/R2 is awesome. If it was jumped the way you said above then it looks backwards from the way the pot was used originally with the signal going in the exit and being grounded in the input side? Below is the schematic that way you suggested. If you look where it is jumped compared to before, the R29 side is the input and the R27 side is the output. Maybe it doesn't matter which side is the input or output? But, the way it was jumped was the way I had it originally based on deafelectro's pictures (above). Looking right at the board where C27/R28 are placed on the board, the schematic and where the jumper was is why I put it that way on the schematic. I say all this because I believe the schematic I am posting here to be not what has been already tried and tested to work but, it is here to take a look at:

http://i29.photobucket.com/albums/c257/t_achin/guitar/v5schmaticmodv23jimp.jpg

Anyone have any comments?

[timothymegg]

First off I would get a clean copy of the schematic either from a post or Crate. Then go through all the posts here that should give you an idea of what is going on in and with the amplifier. As stated way back this amp by design is a solid state preamp (op amp) with a tube output so not ideal. Also it is based off an amp that had an 8 inch speaker that they limited the bass response on. Most of the parts on the amplifier are good except the speaker, screws and nuts. You have a double sided PCB with plated holes I was just looking inside a Epiphone Valve Jr. that has your chepo single sided no plated holes PCB. You also get that 1 Hennery choke in the power supply, iron being a big expense to a manufacture in cost and shipping weight. So anyway go through the posts and figure what mod makes the most sense for you in terms of skill level and the tone you want. For the most bass response adding feedback will extend bass by lowering output impedance therefore reflected impedance at the primary. Also the triode mode will increase bass response by lowering the tube impedance to 2 K ohms from the pentode mode impedance of 35 to 50 k ohms but with loss of output power 1.5 watts and darker sound.

Jim P - looking at Deafelectromark's mod, since C24 is cut out because the OP Amp is removed, what would be a way to increase the bass response or is there no need to do so?

Clean Schematic
http://i29.photobucket.com/albums/c257/t_achin/guitar/v5schmatic.jpg

[jim p]

Just need to correct Timothy’s mark up in post #212. You show one cut to many if you use the vias (holes) from where the op amp was do not cut the trace to pin 3(see attached schematic). On bass response with the op amp in C24 is a high pass filter that is 3db down (half volume) at 270Hz so if you removed the op amp bass response will be fine. If you use the op amp should change C24 to 100nF to lower bass to approx 50Hz. Only other way to extend bass response would be to replace transformer with one that has higher primary inductance (for the most part one that is bigger and weighs more). Use feedback this lowers the output impedance which lowers the reflected impedance at primary which lowers bass response. Use output tube in triode mode this lowers the plate impedance that is in parallel with the reflected impedance on the primary to increase bass response. The calculated numbers for these modes using an 8 ohm speaker, stock transformer turns ratio of 20:1 and primary inductance of 8 Hennery (a value I got from testing with AC signal no DC applied)
Pentode mode (stock) approx 60Hz 3db down
Feedback equivalent to ½ output impedance 30Hz 3db down
Triode mode 24Hz 3db down

Note to go as low as 24 Hz will need to replace C1 2.2uf with higher value 10uf or better. Also connecting to a 4 ohm speaker would increase bass response by halfing the reflected impedance.

[letter109]

:rotflmao: Hi all, just a note to say I have installed an 8 ohm Celestion Tube 10 speaker in place of the stock Crate speaker in one of my V5s. Very nice, and heartily recommended: more bottom end, less brittle plasticky high-end, and when in distortion mode, when two notes heterodyne (like on a major third interval) I get this really creamy, warm break-up that sounds frighteningly like Jimmy Page sted of just garbage. And the speaker isn't even broken in yet! My other two V5s will be getting their Tube 10 speakers in the near future.

FYI I got my speaker from Antique Electronic Supply. I play mainly a stock MII Squier Standard Tele I bought new through the V5. . .I can't believe the sound I am getting for a total $350 (for the guitar, the amp AND the speaker)!:rotflmao:

Next I will be trying some of the mods posted twoards the top of the thread. . .I'll let you know what I do and what happens when I cross those bridges. Thanks all for a great thread -Mike:rockon:

[Rampant]

Hi All

Just replaced my standard V5 speaker with a Jensen 8 ohm R10Q.
Vast improvement over stock.
Still deciding whether to risk modding...?

[goonrick]

Hi All

Just replaced my standard V5 speaker with a Jensen 8 ohm R10Q.
Vast improvement over stock.
Still deciding whether to risk modding...?

If you're at all familiar with soldering and the risks of probing into a tube amp, then it's well worth it. I couldn't stand the sound of mine before the mods, but now I love it. I did all the non-committal mods (speaker, tube changes) before I routed around the op-amp and it still sounded terrible.

There is a broad range of changes you can make, and the posts in this thread give you a lot of knowledge and options. I took a rather easy route with mine, combining some of the suggested mods based on my own tastes and mods I've done in the past.

This little amp is an excellent platform to get into modding. The PC comes out of the chassis quite easily and it's got a lot of room on the board for component changes.

I highly recommend doing a mod of some form or another. Check Jim P's notes on the output and power sections. Then pick and choose from the preamp mods based on the various posts and approaches.

[jim p]

From a RCA Receiving Tube Manual:

"A corrective filter can be used to improve the frequency characteristic of an output stage using a beam power tube or a pentode when inverse feedback is not applicable. The filter consists
of a resistor and a capacitor connection in series across the primary of the output transformer. Connected in this way, the filter is in parallel with the plate load impedance reflected from
the voice-coil by the output transformer. The magnitude of this reflected impedance increases with increasing frequency in the middle and upper audio range. The impedance of the filter,
however, decreases with increasing frequency. It follows that by use of the proper values for the resistance and the capacitance in the filter, the effective load impedance on the output
tubes can be made practically constant for all frequencies in the middle and upper audio range. The result is an improvement in the frequency characteristic of the output stage.

The resistance to be used in the filter for a push-pull stage is 1.3 times the recommended plate-to-plate load resistance; or, for a single-tube stage, is 1.3 times the recommended plate load
resistance. The capacitance in the filter should have a value such that the voltage gain of the output stage at a frequency of 1000 cycles or higher is equal to the voltage gain at 400 cycles.
A method of determining the proper value of capacitance for the filter is to make two measurements of the output voltage across the primary of the output transformer: first, when a
400-cycle signal is applied to the input, and second, when a 1000-cycle signal of the same voltage as the 400-cycle signal is applied to the input. The correct value of capacitance is the
one which gives equal output voltages for the two signal inputs. In practice, this values is usually found to be in the order of 0.05 microfarad."

This is like reading old English or Shakespeare they even have that cycles per second thing going on what’s it all mean?
It’s gotten quiet out there and thought people were running out of things to do so thought I would bring up another mod. As it states above the impedance of the speaker you are driving is increasing in impedance with increasing frequency. Because for the most part it is an inductor whose impedance is equal to 2 Pi (2 * 3.14) times frequency times inductance. Now if you are using feedback as it states above the feedback will correct for this and you should be fine. But what if you like that overdriven sound then feedback is a problem and maybe things are a little shrill or a bit of ice pick tone is happening. Well then if we level off the high frequencies maybe life will be good and that is what putting a resistor in series with a capacitor across the primary will do. From what I am finding on the web the values of choice for this are a 600 volt 47nF cap and a 5k 10 watt resistor so things should start to happen at approx 700 cycles per second (Hz).from above the resistor should be 6.5k(1.3 times the reflected impedance) so? Also instead of power going to the speaker you will be dropping some of it across the watt wasting 5k so maybe just dropping some will work say 10k instead. Also instead of 700Hz starting at 1 kHz might be better then the cap would be 33nF instead of 47nF or starting at 350Hz might be better so a 100nF cap would be your choice. Bottom line if you don’t have a waveform generator and scope you might need to play around with values and if you do have a scope you may still wind up playing with values. Another thing to consider is the turns ratio on the Crate transformer is 20:1 so the primary with 8 ohm speaker is 3200 ohms.

After all this I would just try what everyone else has done before the 5k 10 watts and 600 volt 47nF for a start and see how it goes. Be careful with wiring one side is the plate supply at approx 300 volts and the other is the plate of the output tube that can go to peaks of approx 600 volts at high signal levels. Also if you plan to have a switch to cut the filter in and out I would put it on the plate supply side but still there will be 600 volt peaks on switch contacts with the switch off(so don’t use a little itsy bitsy switch). Also there will be big peak to peak signal voltages on the leads so keep them away from the preamp section (12AX7). If you use a switch the plate supply lead is at AC ground so twist the wires to the switch so this lead will act as a shield. Also check things carefully because you could short the plate of the tube to the plate supply so use your ohmmeter and check before powering up.

Oh and another thing on the web some people think this filter is to correct for the output transformer that is not what the old guys at RCA were saying above it’s the speaker.

It would be nice to know if things are working for people out there so? Thanks

[rock_mumbles]

Hi Jim,

I have put Conjunctive Filters (CF's) on two amps. I've used a 1nf capacitor on one amp and a 2.2nf capacitor on the other, the 2.2nf is used by a high end amp builder. You just want the CF to take out some of the EL84 harshness without changing the overall sound.

From what I've read an amp will sound muffled (blanket over the speaker) with a 47nf or 22nf cap.

On the Gear Page Steve Ahola has posted about putting a CF on a Crate V18 here: http://www.thegearpage.net/board/showpost.php?p=5183840&postcount=63

[jim p]

What I posted is what the old guys at RCA had in the handbook and approx the same values in the “sewatt” web site octal mod I found on the web the other day. Also it tracks the impedance curve of the Jensen MOD speaker I posted. As I said you may want to play with values especially if you are just trying to kill a little high frequency ringing. Good chance a 10k to 20k resistor would do fine and not waste as much output power (need to increase cap values to stay in same frequency range). You will loose high frequencies but there is the tone control and boost in preamp section to make up for that. With a value like 2.2nf and 10k that starts to kick in at approx 7.3kHz so there you must just be knocking off some high frequency ringing, so it all depends on what you are after. Also the problem could be before the output and you are correcting it after the fact at the output transformer. But if you are doing mods with just a meter, soldering iron and assorted parts no way to really tell. Even with a scope and signal generator things may not be obvious. So all food for thought, you actual mileage may vary see dealer for details.

Also what is with conjunctive I thought that is a verb that ties two things together or another name for pink eye?

[rock_mumbles]

Hi Jim, since you know and really understand this stuff and I'm just a hack ...

I read a post on sewatt.com about using a conjunctive filter to keep the grid at the proper voltage in reference to the plate voltage. Can you explain this a bit more???

Thanks!

[jim p]

If the post was by Fondue then I am the one behind the post.

What I was getting at if that is the case is that you may be using the conjunctive filter to mask an oscillation that is occurring due to the screen grid being more positive then the plate during the negative swing of the output signal. What will happen then is the screen grid current will increase so its voltage drops then current flows back to the plate then screen grid voltage rises and the cycle repeats so you have an oscillation.
Two ways to try to stop this are to lower screen grid voltage which is probably the best way to go. Second is to add a grid stopper resistor such as the 470 ohm resistor already on the V5 (but not on stock Valve Jr) connected to the screen grid. If needed the value of this resistor could be raised as high as 2.5k

The screen grid should only attract the electrons and have little current flow, it is meant to increase the gain of the tube and isolate the plate from the cathode for better bandwidth. Any current flow to the screen grid is a loss of signal to the output (speaker) of the amplifier. Lowering the screen grid voltage will lower the gain of the output tube but only marginally.

The grid stopper resistor will increase the voltage drop of the screen grid with grid current which may just be changing the frequency of oscillation in the output tube.

The values you posted for the conjunctive filter were in the 7 kHz range from what I recall which would be in the range of masking an oscillation. Although if the speakers impedance does keep rising with frequency (which it probably does) it would put a limit on the highest impedance the primary of the transformer will see which is probably a good thing. Also no reason not to roll the amplifiers output off out side of the range of the guitar and its harmonics, and I doubt the speaker could reproduce a frequency that high.

The only way to find out for sure what is happening would be to check the amplifier out with a scope while it is driving a speaker at volume and hope to catch the transients.

PS: I am just in the process of replacing the output transformers on a couple of Valve Jr combos and found that I added a filter on the first one I am modifying. It has a 1nf with a 4.7k ohm in series which is 34 kHz not sure I needed it. The amp also has FET voltage regulators for plate, screen and preamp section but I can’t find a marked up schematic for what I did. A good thing to do is mark up a schematic of how your amp is wired and keep it with the amp. In the old days they use to have a schematic glued to the inside of the cabinet on radios, amps ect.

[jim p]

While replacing the output transformer on a Valve Jr combo with an Edcor GXSE 10-6-5K then measuring it’s low frequency response (-3db@ 100Hz) I decided to check the low frequency response of the stock Crate output transformer was amazed to find it is -3db @ 40 Hz with a 6 ohm load. It is just -1db at 80Hz which is the low end of the guitar, so any loss of low end on this amp is in the preamp section.

Nice to here if anyone’s mods are working out there.

[SciHi]

low frequency response of the stock Crate output transformer...

I have played and listened to similar "SE Charming Leah" mods to the crate v5 and valve jr done by Rock Mumbles. The tone and amp response is very good and similar for both amps. But the value jr puts out more volume for equivalent gain and distortion levels. Rock attributes it to the iron in the valve jr, Hammond 125ESE versus stock v5 OT. We haven't tried any other OT in the v5, but the 125ESE are a major upgrade for the valve jrs. Do you think it would help the v5's?

[jim p]

Well you will be down on output volume with the stock Crate output transformer because of the 20:1 turns ratio. Not sure why Crate used this ratio maybe so you can just plug in anywhere from 16 ohm to 4 ohms for the speaker load with just one secondary output. I never checked out the Hammond transformer did not want to spend around 60 bucks to upgrade the Valve Jr’s I have. So I went with the Edcor GXSE 10-6-5k for 25 bucks each for two with shipping. I would think the bass response of the stock Crate transformer should be close to or equal to the Hammond ESE.
The secondary to primary load for the Crate is
4 ohms : 1600 ohms
8 ohms : 3200 ohms
16 ohms : 6400 ohms
Having only 3200 ohms on the primary (with 8 ohm load) will also improve the bass response. But you will take loss of around 35% in output power. So you will get more output with the Hammond for a 60 buck investment or you could change to a 16 ohm speaker.
I didn’t think anyone is going for output volume with these 5 Watt amps anyway?

PS You said that the tones and distortion are similar for both amps that would mean the ideal primary impedance what is it 5k for EL84 6.5K for a 6V6 rule may not be true?

[SciHi]

I didn’t think anyone is going for output volume with these 5 Watt amps anyway?

Thanks. A pair of valve jrs is the stage setup for the blues trio Rock plays with. He admits the v5 is a great bedroom amp, and as you say, is not ready to put $60 (another 125ESE) into a $80 amp. We have been discussing some other OT options, more in the $25 range. He had the version 2 valve jrs and had to upgrade the OTs. I will likely mod my v5 for my son-in-law that likes heavy distortion drop-D, and stick with valve jrs...

[jim p]

The ones that I can think of are the Hammond _SE models guess can go by rule of thumb more they weigh better the bass. There is the OT8SE but I think I would spring for the OT10SE few bucks more should have better bass they have two primary taps for 5k or 6.5k I think and 4, 8 and 16 ohm secondary. Then Edcor they just have single secondary tap the primary has an ultra-linear tap that I might try out. I got the GXSE 10-6-5k so it would be between 4 ohms and 8 ohms bass was -3db at 120Hz with 6 ohm resistor. For 30 bucks instead of 20 could jump up to GXSE 15 they are a pound bigger then the GXSE 10 (1.75 lb) so the bass should be better guess there are others to choose from.

[SciHi]

... the ideal primary impedance what is it 5k for EL84 6.5K for a 6V6 rule may not be true?

I think they say ~6.5K can be used for either EL84 or 6v6, but not the best for either. Maybe it is 4-5K for EL84s and 7-8K for 6V6?

[tunghaichuan]

I think they say ~6.5K can be used for either EL84 or 6v6, but not the best for either. Maybe it is 4-5K for EL84s and 7-8K for 6V6?

Just a few thoughts from modding Valve Juniors and building tweed Princeton circuits:

I've used the Hammond 125ESE with both 6V6s and EL84s and it seems to work well using the 5K setting.

In one Valve Junior rebuild (chassis gutted and rebuilt with an eyelet board and NOS tubes) I used a massive Heyboer OT. It was rated conservatively at 160mA on the primary. It had 2.5k, 4k, and 6k primary impedances. I tried both 4k and 6k for use with the EL84 and 6k sounded best to me.

I've used a 125CSE in a Valve Junior circuit and I thought it sounded too bright and gritty, the 125ESE was a major improvement to my ears.

I've probably built over a dozen amps using tweed Princeton circuit and various combinations of tubes. About half were built using the 125ESE and 6V6 tubes. On one amp I substituted an Edcor XSE15-8-5k OT for the Hammond. To my ears the Hammond sounded better when the amp was pushed into distortion. The Edcor sounded better clean.

FWIW

tung

[Fonzie]

A few pages back, there was some discussion about which speakers will fit in the V5. I just put an eminence Patriot Ragin Cajun in mine and it fit with no problem; which surprised me since I measured everything first and thought that no way it would fit.
I also put in JJ EL84 and ECC81 while I had it apart.
Noticeable improvement in sound especially with my overdrive and distortion pedals. The stock speaker sounded like an angry can of bees, the Eminence sounds, well, like a speaker should sound.
I also plugged the V5 into my Deluxe Reverb cabinet with a Weber 12F150; The 12" speaker has some better warmth, but, considering that the Weber cost more than the whole V5 amp (I got mine at BestBuy for $50) i think the V5 is just fine. I might improve the board if I get brave enough, or just ship it to Mark Deafelectro because he is cool.

Mike

[SciHi]

The secondary to primary load for the Crate is
4 ohms : 1600 ohms
8 ohms : 3200 ohms
16 ohms : 6400 ohms
...

Jim, on the 6v6 mod earlier, http://www.thefret.net/showpost.php?p=124456&postcount=58, did you stick with the stock v5 OT? Are you saying running a 16 ohm speaker will make the OT more 6v6 friendly? How did that 6v6 mod turn out? As you say with the extra heater capacity you could power another preamp tube for a cascaded preamp, similar to the new Plexi Junior SE build.

[jim p]

What I was getting at with a 16 ohm load you won’t loose the watts at the output you are with an 8 ohm load. Power is equal to current squared times impedance (resistance) so do to the fact that with 8 ohms you are only 3200 ohms reflected instead of 5000 you are loosing power. While with 16 ohms you would have 6400 reflected and not have the loss. I don’t know about the whole 7k is better with this tube 5k with that thing I used the stock transformer with the 6V6 tube when I moded that amp. As I stated the heater current is less for a 6V6 by a factor equal to the current required for a 12AX7 so I may add a third tube to the third amp I have. But I may go with a signal pentode that I will overdrive before the output to see how that works.
I am thinking of dropping the plate supply on the V5 to up the plate current so it might give you greater output power with the stock transformer. But first I need to replace the stock (junk) output transformer on a VJ combo ver 1 amp and may give the ultra-linear mode a try with that.

[SciHi]

As I stated the heater current is less for a 6V6 by a factor equal to the current required for a 12AX7 so I may add a third tube to the third amp I have...

So we aren't running the opamp, so can we gain enough current from the existing 12.9 volt preamp heater circuit to run the second preamp tube ? The PT has 6.3 volt for the EL84 separate from the opamp and preamp heaters (+14.5,0,-14.5).

[SciHi]

...I used the stock transformer with the 6V6 tube ...

So the stock setup has R4-C23, Zobel (?) network, across the output to the speaker. So isn't this to correct an issue between the speaker and OT? So is the problem with the speaker or OT?

When you do your variable nfb you mentioned over on SEWATT, do you just connect at R4?

[jim p]

That RC network (R4, C23) on the secondary of the output transformer by my calculation doesn’t do anything till approx 160 kHz so don’t know the point in it. As far as variable negative feedback check post #201 I have a schematic and description of how to do it there.

Regarding heater current I was going to hook up the third tube to the 6.3 volt AC heater supply. I am running a tacked in 6CB6 pentode to try things out as far as adding a pentode for overdrive with the stock EL 84 and so far no problems. If things work out will switch to an EF86 for the pentode (wish they were cheaper). The heater supply is on the high side (should be 6.3 volts +/- 5%) so in future may look into adding a resistor in series.

Removing the op amp only frees up 10mA of current at best if you were going to use the +/- 15 volt supply for heater current. If I used one of those supplies I would go with the -15 to balance the load on the secondary. I see at Sewatt that they look to be adding all kinds of loads on the stock VJ transformer I wonder how they determined that the transformer is ok with the added loads?

[SciHi]

As far as variable negative feedback check post #201 I have a schematic and description of how to do it there.


Thanks. The schematic posted at SEWATT has the pot on the ground side of the the cathode bypass cap (cap needs lifted for nfb to work). I think that is correct, not as shown in the schematic in post #201???

[SciHi]

If things work out will switch to an EF86 for the pentode (wish they were cheaper).

Has anyone tried the Russian tube equivalents? " NOS RUSSIAN tubes (6J32P)/6267/EF86 " We have had good results with some of the Russian EL84M's.

[SciHi]

What I was getting at with a 16 ohm load you won’t loose the watts at the output you are with an 8 ohm load...

Jim, I think you really have something here! So I hooked up to my 2-12 cab, 2 - 16 ohm speakers in parallel. Put one on a switch so I could go from 2-12 at 8 ohms to 1-12 at 16 ohms (Jensen mod 12-70). Sounds much, much better with the single 16 ohm speaker, clearer, fuller (bottom end), and louder!!! I will have to try the reverse with 2 - 8 ohm speakers hooked up in series to really nail this one.

OK, just tried it with 2 - 8 ohm 10's in series. Sounds better at 16 ohms. So I think I will shop around and try to find a mod 10 in 16 ohm, I checked out the weber sig 10s and they are only available in 8 ohm.

So what's the downside with the 16 ohm load, is it harder on the EL84? (nothing died yet)

[jim p]

In the schematic for the negative feed back there is an X through the cap not to clear in the picture. Removing it is also in the text describing the mod. As far as the order of cap and pot and which is tied to ground doesn’t matter much.

On rethinking if the pot is at ground then the wires to the pot will be a twisted pair with one lead at ground so may be better for noise reduction wired with pot at ground.

I figure to go with the EF86 pentode because it looks to be an available standard part now, plus the mesh screen inside of the tube looks cool. If the pin out of the EL84 is the same I might look for that.

On to a 16 ohm load on the amp I don’t see that it should be a problem the primary impedance will be 6400 ohms instead of the standard 5000 ohms which should not be too bad. I forget where the plate voltage is at this point but at most may pay to keep it at approx 300 volts but without scoping it out that is just speculation.

[timothymegg]

Post #168: No OP Amp, No Jumper Mod...

Options:
Short R30 or R29 and remove C28 for more maximum signal at grid of second triode.
Replace loss of pre emphasis for tone stack by replacing C1 with a 200nf cap so tone control will be treble boost, flat and treble cut. Or instead change R9 to approx 220k and add a Resistor and capacitor in parallel with it for treble boost.

I did the mod last night and, WOW!! The options above are the ones I haven't done. My only complaint is that the tone stack seems to do VERY little. I did remove C4 and C5. And, with a Route 66 pedal on the compression side the tone knob seems to give me back all the treble that I want. I would like to be able to get some treble with the tone stack on the amp. So, my question is about the C1 replacement to 200nf... I don't have one. Can I use a different one of say 0.47uf (same as 470nf?) or 0.1uf (100nf?) because those are what I have? :confused: (both are 50V) What would be the tonal difference or effect?

I am very happy with the mods because now my amp sounds like a guitar amp. It is my first guitar amp and first time modding a circuit board. I am very thankful to deafelectromark and jim p for all there ideas and support!

Peace, Timothy

Edit: I realized I forgot to remove C25 :thwap: as I was marking up the schematic. After I did there was a lot more volume overall (guessing I was dumping some of the input signal to ground before I removed C25?). After I removed C25 I still wish the tone knob would do more so the same question above stands. Thanks

Schematic as I modded it:
PS: I didn't cut a trace between the wiper and the output of the volume pot and it works fine. jim p suggested before that it be cut but, I don't no where to cut it? deafelectromark didn't cut it either (from what I could gather?).
http://i29.photobucket.com/albums/c257/t_achin/guitar/v5schmaticmymod.jpg

[jim p]

Timothy what you have shown on the marked up schematic has to be in error because the input to the second triode is grounded. With things working my best guess is you really have the pot as a variable resistor to ground that is tied to the control grid of the second triode with the control grid also connected to R15 or R29.

On to getting more treble by changing C1 do you have two 100 nf (0.1 uf) caps if so two in parallel is equal to 200nf so you could use that at C1 for a treble boost. Just using 100 nf at C1 won’t start to have an effect until 1 kHz so may not be early enough. While 470nf (0.47 uf) will start at 225 Hz which is a little low. Using 200 nf (0.2 uf) the boost will start at 550 Hz. In the case of voltage rating 50 volts is plenty you could get away with 12 volt rating easy.
You can also put two 470nf caps in series for 235nf that would be close enough to 200nf at C1 location.

[timothymegg]

Timothy what you have shown on the marked up schematic has to be in error because the input to the second triode is grounded. With things working my best guess is you really have the pot as a variable resistor to ground that is tied to the control grid of the second triode with the control grid also connected to R15 or R29.
It most definitely works ;) It is the way deafelectroark did it in his mods.


On to getting more treble by changing C1 do you have two 100 nf (0.1 uf) caps if so two in parallel is equal to 200nf so you could use that at C1 for a treble boost. Just using 100 nf at C1 won’t start to have an effect until 1 kHz so may not be early enough. While 470nf (0.47 uf) will start at 225 Hz which is a little low. Using 200 nf (0.2 uf) the boost will start at 550 Hz. In the case of voltage rating 50 volts is plenty you could get away with 12 volt rating easy.
You can also put two 470nf caps in series for 235nf that would be close enough to 200nf at C1 location.
I don't have two of either, I have only one of each. I am curious though, what does the 2.2u C1 stock cap do? Is it more of a mid boost? And, if I use the 100nf will it slightly or greatly increase or boost the treble? I'm just looking for a little more sparkle and not shrill.
Thanks for the quick response: you rock! :AOK:
Timothy

[jim p]

The stock value of 2.2uf for C1 will bypass resistor R3 starting at 50Hz so you get the maximum gain from the first triode minus some 60 Hz (line frequency noise). By going with 200nf the gain is only half (27) for the low frequencies up to about 550 Hz. Then the gain will rise up to the maximum of approx 54. So by changing to 200nf you will drop the gain on the bass to get boost for treble (highs)

[SciHi]

It most definitely works ;) ...

So maybe the jumper from the volume pot to R27 is not on the ground side of the removed resistor, then it would work as a variable resistor???

[jim p]

So maybe the jumper from the volume pot to R27 is not on the ground side of the removed resistor, then it would work as a variable resistor???
I think how his mod works is how I described a similar mod in post #168. The pot is a variable resistor to ground at the control grid of the second triode.

[stoneattic]

Options:
Remove R7 for higher maximum signal on grid of second triode.
Short R30 or R29 and remove C28 for more maximum signal at grid of second triode.
Remove C27 and use the vias (plated holes) in the PCB to connect rheostat (pot) to location of R27. Makes for shorter jumper runs on PCB.
Replace loss of pre emphasis for tone stack by replacing C1 with a 200nf cap so tone control will be treble boost, flat and treble cut. Or instead change R9 to approx 220k and add a Resistor and capacitor in parallel with it for treble boost.


I did the no-opamp mod that jim p posted back in post 168 and it was a huge improvement! I also found an old 10" guitar amp speaker of somewhat unknown origin but figured since it had a much larger magnet and was paper instead of plasitic it had to be better and it sure is!

I didn't do the options jim p posted figuring I wanted a base line sound to compare before making the mods. I have a couple of questions that i hope jim p, or anyone might be able to answer.

What does "maximum signal at the grid of the second tirode" mentioned in the options to the mod do in terms of volume, overdrive/distortion, etc?

I use this amp as my living room practice amp so generally the more overdrive/distortion at lower volume the better (within reason). I've wondered if adding another pot to control volume between the second tirode and the EL84 would act as a master volume and allow me to get more distortion at lower volume via preamp overdrive, although preamp overdrive is generally not as smooth as power amp overdrive.

[tunghaichuan]

You might want to check out this blog post:

http://yeomansinstruments.blogspot.com/2008/07/vvr-greatest-thing-ever.html

The VVR will allow you to dial down the plate voltages to get the power section to overdrive faster and at low volumes. It won't sound exactly like a cranked amp because it isn't pushing air.

You can buy a VVR PCB from this site:

http://www.hallamplification.com/main.html?src=%2F#2,2

tung



I did the no-opamp mod that jim p posted back in post 168 and it was a huge improvement! I also found an old 10" guitar amp speaker of somewhat unknown origin but figured since it had a much larger magnet and was paper instead of plasitic it had to be better and it sure is!

I didn't do the options jim p posted figuring I wanted a base line sound to compare before making the mods. I have a couple of questions that i hope jim p, or anyone might be able to answer.

What does "maximum signal at the grid of the second tirode" mentioned in the options to the mod do in terms of volume, overdrive/distortion, etc?

I use this amp as my living room practice amp so generally the more overdrive/distortion at lower volume the better (within reason). I've wondered if adding another pot to control volume between the second tirode and the EL84 would act as a master volume and allow me to get more distortion at lower volume via preamp overdrive, although preamp overdrive is generally not as smooth as power amp overdrive.

[jim p]

You could put in a master volume before the output tube but just as the previous post states and you said that would be an overdriven triode not the output tube. I have not done the FET source follower variable regulator on the plate supply myself so I can’t give an opinion on it. I have varied another supply in the output section with good success for distortion at low volumes using a source follower.
Your other choice would be an L-Pad between the output and the speaker, not quite the same because more of driving a resistive load instead of a speaker (inductance, capacitance and resistance)
If it is the variable voltage regulator that is on the SEWATT web site adding a 100nf on the gate of the FET should improve power supply ripple rejection. Also in the schematic showing the circuit it in the amplifier there is a diode in series that on power down would unhook and leave filter caps charged. That could be cured by adding a diode across the FET that would be forward biased on power down. I may post a marked up schematic there to pose the question to the folks over there.
Right now I am looking at adding an overdrive channel to a V5 using a signal pentode as the overdriven tube. For now I am using a 6CB6 from a lot of tubes I bought on E-bay awhile back. It is not sounding too bad I ordered four tubes on E-bay from the Ukraine that are the Russian equivalent to an EF86 if all goes well maybe will post a mod to show how to do it.

[stoneattic]

The VVR sounds very interesting and probably better than a master volume. i may give this a shot.

This is a cathode bias amp correct? (I want to be sure and order the correct part)

[tunghaichuan]

The VVR sounds very interesting and probably better than a master volume. i may give this a shot.

This is a cathode bias amp correct? (I want to be sure and order the correct part)

Yes, it is cathode bias. The cathode bias resistor is R17 on the schematic.

tung