Crate V5 mods... anyone?

[Christopher Whitlow]

Here is a list of things to check and ohmmeter to see if the connections are correct.


With the op amp out you should have C24 C25 and C26 removed with a jumper from pin 3 of the op amp to the junction of R1 and R2 with R2 removed. That is the signal from the guitar to the first triode. Pin 7 of the op amp should be grounded C27 removed R27 should be removed with a jumper from the junction of R27, R7 and R15 jumpered to pin 6 of the op amp. C6 should be installed R15 should be installed. If you ohmmeter from the tip of the ¼ inch jack to pin 7 of the 12AX7 you should read the value of R1 47k also check to ground should be 1 Meg. Ohmmeter pin 2 of the 12AX7 to ground you should have zero with volume pot turned down to 250k at volume at full clockwise. From pin 2 of the 12AX7 to R9 should read approx 500k to 600k.

Another source for amp modifications and help is over at sewatt.com

You are awesome! I know already that one problem will be me not realizing I interrupted the flow when I did the second mod by NOT replacing c6 or c15. Amazing what you miss when you dont know what to look for. I have a multi meter and will check values at those critical points a Bnd replace my missing parts in the signal path then report back. I have the book mentioned above on it's way and Im learning a bunch from the pdf that explains amps in the 70's and before. When I recieved this amp free I decided this was my chance to learn how they work and boy howdy am I a learnin! Thnx again folks!

[vinyl_key]

Hey all, proud owner of a V5 that I modded per post #168 ~2 years ago with a few questions after re-reading all 23 pages of this thread :

My current set up for my Crate is: op-amp removed and stock 12AX7 replaced with a 12AT7.

• What are some ways to make the tone control act like like a normal tone control. I've seen mentions of changes to the tone stack in this thread, but they're a bit hard to follow what's going on with more than half of the images gone.
• Will a Weber Signature AlNiCo 10 fit in? The depth is longer than the 4" that will fit, but it looks like the magnet (with the cover removed) is skinny enough to just stick past the amp enclosure. If the AlNiCo doesn't fit, a Sig ceramic will make do.

Thanks for the wealth of information in this thread

[SciHi]

• What are some ways to make the tone control act like like a normal tone control. I've seen mentions of changes to the tone stack in this thread, but they're a bit hard to follow what's going on with more than half of the images gone.

Since the stock tone pot has the wiper to ground, I converted it to a Marshall normal channel tone control. I can post a partial schematic for this mod when I return home after the 4th... http://mhuss.com/18watt/schematics/18wattLite.gif

OK, maybe this will help.

[jim p]

The Weber AlNiCo will fit without the shielding around the magnet. You could consider the Eminence Legend 10516 as a speaker choice also. The output transformer impedance is really 16 ohms so you may want to get a 16 ohm speaker. On the tone control if you remove C5 and C4 and change C1 to 470nF then the tone control will be set to bass at CCW and treble at full CW. The op amp used to boost the treble so to make up for that changing the first triode bypass cap to 470nF will make up for not having the op amp boost.

[SciHi]

I was talking with Rock Mumbles this evening and he reminded me of the power tube fixes for this amp. First, the screen resistor needs moved to the correct position, then the EL84 bias needs corrected, depending on the size of the cathode bypass cap, 240-270R cathode resistor. I also added a master volume but it is not necessary...

[rock_mumbles]

I was talking with Rock Mumbles this evening and he reminded me of the power tube fixes for this amp. First, the screen resistor needs moved to the correct position, then the EL84 bias needs corrected, depending on the size of the cathode bypass cap, 240-270R cathode resistor. I also added a master volume but it is not necessary...

I used a 240 ohm cathode resistor and wish it was still a bit smaller, although I do have a 100 ohm (not-a) sag resistor that drops a few volts. My plate voltage is now 297V and the screen is 289V, prior to reworking the dropping resistor and screen resistor the screen was about 310V and the plate about 300V ... not good ...

I love this amp with the circuit I now have in it, I pulled the minimum number of parts to be able to rework the circuit.
First I pulled both pots, the stock op-amp gain control for the volume control ??? what were they thinking, and the tone pot mess, although if you want to leave the tone pot in circuit it can be rebuilt to the Marshall 18 Watt "normal" tone control, which works really nice for a Marshally V5.

I pulled R1, R9, R10, R15 and R27. I cut R7 as it's mounted on top of the socket (it might not be a bad idea to cut D9 and D10, so theres no power to the op amp even though it's not connected to anything anymore)

The easiest way to redo the input to bypass the op amp and associated circuitry is to jumper R10 and run a 68k (or less) resistor from the right R10 via (pcb hole) to the top R1 via, closest to C1. You should be able to place the input resistor lead into the right R10 via and bend the lead over and up into the left via to form the jumper. I put insulation tubing on the exposed input resistor leads.

For V1a, R3 gets switched to a 2.7k and C1 to a 0.68uf (film)

V1b is fine stock

R17 the EL84 cathode resistor is way too large at a 330 ohm it should be about 240 ohms.

Instead of just moving the screen supply like SciHi showed above, I replaced R25 with two resistors in series, put two 2.2k 2 watt resistors in series one leg goes into the R25 via (pcb hole) closest to C16, I put the other leg into the left via labeled R23 (unused) then I connected the left leg of R18 (screen resistor) to the junction of the two 2,2k resistors.

Then for the tone control/volume pot, I used the Framus mid control with a 500k Audio volume pot. The left via of R9 (closest to C2) is used for the tone control input and the volume control output connects to the left via of R27
here's a schematic of the tone/volume control ...

[bcdon***]

That is some serious hacking, very interesting!

[rock_mumbles]

It's completed, to tame the highs a bit I ended up putting a 680pf cap across R6, that did the trick.

I pulled the Weber Ceramic Sig 10 (smooth cone) and replaced it with a new Jensen C10Q I picked up for $20 ... I decided I wanted to keep the Weber Sig 10, it sounded a lot better in the Crate combo cab, fortunately the Framus mid control deals with the boxy heavy midrange tone of the Jensen pretty well.

The Weber Sig 10 is a nice affordable speaker for the Crate V5, it sounds really good in the small Crate combo cabinet. With my Strat the Jensen C10Q (which has a larger magnet and just barely fits) has a bit too much of a midrange dominant tone (for me) ...

I agree with jim p that the Eminence 1058/10516 series speakers are really nice sounding, it was the best sounding speaker we tried in my brother's Vox AC4TV ...

[vinyl_key]

Thanks for the info!

Got my Weber AlNiCo Sig10s in the mail today, sounds much better! Can't wait till the speaker gets fully broken in. Now all that's left is to get the tone circuit to my liking.

[Maarten Aerts]

Found this thread again today.
signed in to share my results with the V5.
(Intro: played bass for 35 + years and home guitar, but recently tried to play guitar in a band because i got this amazing Epiphone dot studio es335. And it's fun to rock.)

Also bought the crate v5 about six months ago, and found the modding fora....

The mods described here were way to scary
I instead did the following, combined from other fora:
Changed the speaker with a Celestion tube 10.
Changed the tubes:
1 x JJ EL84 / 6BQ5 Matched (TF-0987)
1 x JJ 12AX7 / ECC83S (TF-3645) (also tried others, not nice)
Replaced R17 with a 150watt 5 ohm resistor because the bass distorted ugly .

Loved the sound, wished it could get louder to play on stage.Use it every day at home.

The amazing thing is, my marshall jcm900 4501, was always failing when played on higher volume.
The store were i bought it couldn't find the problem, so i kept in as a home practice amp. (to shy to make a big noise about warranty those days)
On low volume it was exellent, but totally unreliable for stage.

And now i finaly had dared to solder on an actual tube amp (R17)- i had the courage to open up the marshall and found out that the pins of the things the tubes go into weren't soldered right.
If really hot, they would lose contact....
Now a have my big amp again and a really nice little V5, thanks to these fora.
love it with its cleanish blues tone and distortion with a carl martin pedal.

And after re-reading all these pages i think i will do the no-op amp mod.
I understand a lot more now

Hope i won't spoil it

[Maarten Aerts]

Since the Crate was to have more output with 16 ohm, i put some input-jacks together to make plug 2 x 8 ohm speakers out, and 16 ohm in.

Tried the celestion of the marshal with the internal tube 10 (crate), it is amazing, so loud! With the 335studio it made the tonepot usefull, jazz, blues.Pedals worked great.
Way to loud for home-use. but full sound.
With my 10" swr-basscab it was also really loud, and a nice sound, but not as much big warm open in the lows.
So i need a 12" cab with 75/100 watt celestion G12 and the jacks wired for 16 ohm, no need for soldering. (A Jensen would be to much mid-high i think)
Thanks again for the valuable info

Back to playing now

[cebreez]

Hello All!! My name is Terry Smith.... I am a new member to this forum but I've been pouring over it for weeks. Have had my Crate V5 for at least as long as this thread has been up and it has actually seen very little use since I regularly play through a Peavey Classic 30 1x12 even when I practice. Though lately I've wanted to have a more portable setup when away from home so I got the old Crate back out in hopes of modding it a bit. This is a great thread and jim p you are my hero.... BUT!! Here is my quandary.... I want to keep the op-amp.... Round out the tone.... and increase the headroom. I've liked some of the mods that move the volume pot and deal with the tone knob... I know Im behind but (why?) would we have the tone controlled by the op-amp to start with...? Would it not serve better after the op-amp......? If this all sounds confusing it is because I am very confused!... (and going blind ) I actually found an old 10" speaker from an Alesis Wildfire I had laying around... It fit after some coaxing but made a huge difference in tone and headroom. Now I am ready for new tubes and whatever mods you fellas deem absolutely necessary to capture of little more of that Fender magic. Any help would be GREATLY appreciated.

P.S. Im not scared to mod anything. Just want to make sure its worth it in the end.

Thanks
Terry

[cebreez]

Is this thread dead? HELLOOOO!!!

[SciHi]

Is this thread dead? HELLOOOO!!!

HELLO and welcome. Jim P. had posted very early some fixes if you want to keep the opamp, I think most of use just removed it and modded from there... It is hard to get much headroom, at any volume, out of a single EL84. You can get good overdrive and it will get loud when the EL84 is being driven hard but none of the little 5 watt single end tube amps have much for clean headroom. The speaker is probably the biggest single improvement to the amp, in my opinion, the most important first mod. My experience is the tubes have much less impact, unless you want to run a lower gain tube such as a 12AY7. Put in a decent speaker, and keep the gain turned down and it should at least be usable.

[cebreez]

Thanks SciHi! I was feeling really alone in here! I understand what you are saying. I didn't see jim p's earlier post and what I'm finding out is the older post seem to lose there pictures. Could just be my crappy computer though. I understand what you are saying but let me interject with a personal observation and please feel free to call me foolish. Like I said I know just enough to be dangerous. I built successfully the "Noisy Cricket" amp and at first was very pleased till I realized for old deaf ears it just was not loud enough and broke up way too soon. I know why and thats okay but before I took the soldering iron back to it I did a little test and plugged it into my pedal board to see how close it was to an overdrive circuit. It just made everything louder, much much louder but did not overdrive or distort the signal at all. Why.... ? My point is I believe the op amp circuit in the Crate V5 is doing exactly the same thing. It is not there to overdrive the preamp tube just to compress and amplify the input signal giving us more headroom. When I changed out speakers I got phenomenal results from a relatively cheap speaker with a bigger magnet. Now i would like to use the input circuit(the op amp) and extend the frequency range (more lows and highs) on command with a better tone circuit. I like the op amp because there is so much you can do in that little space and never have to touch the tubes or drive circuit. Like putting a performance chip in your car or cleaner gas and getting better performance without having to crack open the engine. I hope all this makes sense.... it does in my head but then again that is another matter. HA!

Thanks SciHi....

[SciHi]

... Now i would like to use the input circuit (the op amp) and extend the frequency range (more lows and highs) on command with a better tone circuit. I like the op amp because there is so much you can do in that little space and never have to touch the tubes or drive circuit. Like putting a performance chip in your car or cleaner gas and getting better performance without having to crack open the engine. I hope all this makes sense.... it does in my head but then again that is another matter. HA!

Bent on keeping that opamp, well check out Verne's posts over at HC, "Supercharging a V8." http://acapella.harmony-central.com/...rcharging-a-V8

The V8 is the V5's big brother. First thing Verne did was put in a high quality chip! Replaced the TL072, check it out, and Verne is still around and could help out keeping the opamp intact. You can compare the schematics and see where the V5 cut a few corners to "cheapen" up the amp.

Here is a favorite quote of Verne's:

"The problem with the opamp implementation as found on the V8 – particularly the hiss and extremely low amount of clean headroom – isn’t the USE of an op-amp, but the CHOICE of op-amp. The TL072 is a cheap [20 cents in quantity] component that probably introduces as much noise as using a tube, so it defeats the purpose. Because of its low headroom, it actually introduces a bunch of noise that keeps you from really cranking the gain to its sweet spot.

The “fix” is to replace it with a TLE2072. This is one of Texas Instruments Excalibur series and is renown for being the best of the best. You can get this chip from Mouser for around $2.50. The only complicating factor is that SLM soldered the TL072CN to the circuit board."

[cebreez]

P.S. I saw jim p's original post but none pictures were there to show what he did. The guy really knows what he is doing but I had a hard time following his explanations. I wish I had been a member then and gotten into the discussion. I believe he was on the right track but I would have loved to coax him into a different direction. When I get this figured out and eventually I will, I will do my best to post the schematic markups. I totally disagree with the "sledgehammer" idea. This amp is a real sleeper and has almost everything you would find in amps costly "x infinity" more. I am thinking too about a different output transformer to boost this to a 10 or 15 watt amp but haven't gotten past the input circuit yet.

[tunghaichuan***]

P.S. I saw jim p's original post but none pictures were there to show what he did. The guy really knows what he is doing but I had a hard time following his explanations. I wish I had been a member then and gotten into the discussion. I believe he was on the right track but I would have loved to coax him into a different direction. When I get this figured out and eventually I will, I will do my best to post the schematic markups. I totally disagree with the "sledgehammer" idea. This amp is a real sleeper and has almost everything you would find in amps costly "x infinity" more. I am thinking too about a different output transformer to boost this to a 10 or 15 watt amp but haven't gotten past the input circuit yet.

You might have to replace the power transformer as well as the output transformer. Boosting the amp from 5 watts to 10-15 watts is not as easy as it might seem. There are several ways you could go about it.

You could add another EL84 in parallel to give you 10 watts, but you'd have to use an output transformer with half the primary impedance as the existing unit. You'd have to replace the power transformer with one that has double the current capacity as the stock unit.

If you wanted to move up to a larger, single power tube, you could probably get 10 watts out of a 6L6GC tube in SE. But again you'd have replace both stock transformers with appropriate new units.

For 15 watts in SE operation, you'd need to go to a 6550 or a KT88.

All of the above are for single ended operation, and the larger the tube, the heavier the transformers get to handle the increased current. These transformers also tend to be very expensive.

You could completely gut the amp and build in a push pull circuit using two EL84s or 6V6s. But then you have to add a phase inverter to operate the amp in push pull. This is in addition to the existing preamp circuit. The transformers would be smaller and lighter, but the question is: do you have enough room in the chassis for the extra circuitry?

Modding a 5W amp into a 10-15 watt amp is not an economical way to get a killer practice amp. Really, you'd be better off buying a commercial amp that already has the features you want.

[cebreez]

I totally get what your saying and all options that I have considered. Wasn't thinking about the power transformer, good point. Definitely not enough room to start adding more tube circuitry. Larger tube...? Well...? Maybe. Expense is definitely the issue. I have a larger tube amp but not really wanting to go that route. Want to keep this one small and compact. Played with my BBE Sonic Maximizer in front of the Crate today and love the tonal difference it made. Gave it clarity and very nice harmonics. Liked it so much I ordered a pcb for a look-a-like on "madbeans.com". Might try to incorporate that on the input or in place of it. Also considered a nice 4 knob preamp pedal circuit for the same reason. Would add the necessary gain and EQ on the front end while still keeping it clean and low noise.