Crate V5 mods... anyone?

[SciHi]

Which wire should i be using to mod this ? (jumper wire etc)

Jumpers on the pcb, I just use small wire, 22-24 gauge is fine. If it is a single component or very close, I just use the cut off wire leg of a resistor or capacitor. Sometimes I will put the jumper on the bottom if things are packed real tight on top. If I am running to a pot or switch mounted to the chasis and it is a low voltage signal, then I will usually use shielded audio cable, like this, http://www.alliedelec.com/Images/Pro...E/214-1557.PDF mostly because I have access to it. This seems like a better source for amp parts/wire: http://cgi.ebay.co.uk/CABLE-WIRE-600...3A1%7C294%3A30

Old computers are a good source for small shielded wire, usually from the cd drives, this is very similar to what the valve junior uses. Higher voltage, or strong signal can usually be done with twisted pairs. Thanks Dr. Mumbles for adding the specifics...

http://i615.photobucket.com/albums/t...jumperwire.jpg

[rock_mumbles]

Which wire should i be using to mod this ? (jumper wire etc)...

I use wire from a burned out computer power supply to connect volume or tone pots and for runs of a few inches on a circuit board. A friend bought a professionally modded amplifier and all of the jumpering was done with single conductor stranded wire.

In my V5 I jumped around the OP-amp with a new 68K grid resistor, but I reworked the amp circuit quite a bit.

I use (old) computer sound card cables (CD to sound card) when I want to use small shielded cable, but again only for carrying the signal NOT for supplying voltage to the tubes, etc.

One of the main things about the wire you use is the insulator on the wire, some wire is really hard to solder because the insulation melts so easy.

[stoneattic]

I will mark up a schematic and post it but the way you have it configured there is no filter capacitor after the VVR. I think without adding another filter cap the quick and dirty way to solve that will be to replace R25 with a short. Then break the circuit where R26 hooks to C16 you should replace R26 with a 15 to 25 k (it may be best to use 25k) resistor to reduce the plate voltage on the 12AX7. Then R26 will hook to C15 + on one side and C17+ on the other side so it bypasses the VVR.
Another change I would make is to increase the grid stopper resistor value R18 a quick thing to do is to use the 4.7k that use to be R25 there.
As far as the diodes you show not sure you need them and some filter caps will have no bleeder resistor across them so they may stay charged for a while with the amp turned off.

On the master volume if you remove R31 and R16 you can hook a 500k (or 1 Meg) pot to where R31 connected to C7 then the wiper to where R31 hooked to C3 and pin 2 of EL84 and the other terminal of the pot to ground side of R16. May want to change C3 to 100pF or remove it (high frequency roll off). I would just use twisted individual wires to connect to the PCB and pot.

On the master volume and feedback you could have both but you cannot use them both at the same time. When you use master volume the gain between the 12AX7 and output tube is changing with you adjusting volume so no way to know what feedback ratio to use. So you would have to max out the master volume then use feedback so the gain control will be your volume control as if you had no master volume. Also with the Variable voltage regulator the feedback would not work due to gain of output tube changing with changing plate voltage. Plus feedback makes going into distortion abrupt so it would not work well with using variable voltage on the plate supply.

jim_p, thanks for the schematics, etc.

I believe there is a mistake in the schematic for the VVR though. Your text says to replace R26 with a 25K, but the schematic say R28.

I was showing diodes because the instructions with the VVR said they sould be used when using the VVR to control the power tubes only to prevent the two B+ circiut (VVRed and non-VVRed) from interacting.

I'm not following your last paragraph regarding feedback. Are you saying that the master volume and VVR will conflict? Excuse my ignorance please. I'm still learning my way around tube amps. I have a basic understanding of how tubes work and have been doing a lot of reading, but some of the intricacies still elude me.

[jim p]

I'm not following your last paragraph regarding feedback. Are you saying that the master volume and VVR will conflict? Excuse my ignorance please. I'm still learning my way around tube amps. I have a basic understanding of how tubes work and have been doing a lot of reading, but some of the intricacies still elude me.

Thanks for pointing out my error on the schematic; I’ll have to fix that. Still confused on the need for the diodes but they can’t hurt except on the no bleeder resistor aspect.
The last part of the post was just commenting because of another post in regard to feedback and master volume together being a problem. From what I gather you are just adding master volume and variable voltage regulator those two together should be no problem. Hope you are having no problems making the modifications. Probably would be good to post pictures of the mod and details for anyone else considering installing the VVR themselves.

I didn’t go in to detail on changing R25 to a short it will give you a filter cap after the VVR. If you look through previous posts you will find that C16 should have been a filter cap for the screen grid voltage so one side of R18 should have been hooked to it. Figure that the EL84 is ok without the lower screen grid voltage and C16 is really serving no purpose so may as well take advantage of it for this mod.

By changing R18 to 4.7k that will lower the screen grid voltage relative to the screen grid current through it. Also the higher value will be safer for the tube if the plate voltage goes lower than the screen grid voltage and the screen grid current rises. The higher value resistor should provide greater negative feedback and limit the maximum current that might pass through the screen grid.

Hope your mod is going well let us know how it works out.

[stoneattic]

Thanks for pointing out my error on the schematic; I’ll have to fix that. Still confused on the need for the diodes but they can’t hurt except on the no bleeder resistor aspect.
The last part of the post was just commenting because of another post in regard to feedback and master volume together being a problem. From what I gather you are just adding master volume and variable voltage regulator those two together should be no problem. Hope you are having no problems making the modifications. Probably would be good to post pictures of the mod and details for anyone else considering installing the VVR themselves.

I didn’t go in to detail on changing R25 to a short it will give you a filter cap after the VVR. If you look through previous posts you will find that C16 should have been a filter cap for the screen grid voltage so one side of R18 should have been hooked to it. Figure that the EL84 is ok without the lower screen grid voltage and C16 is really serving no purpose so may as well take advantage of it for this mod.

By changing R18 to 4.7k that will lower the screen grid voltage relative to the screen grid current through it. Also the higher value will be safer for the tube if the plate voltage goes lower than the screen grid voltage and the screen grid current rises. The higher value resistor should provide greater negative feedback and limit the maximum current that might pass through the screen grid.

Hope your mod is going well let us know how it works out.

Now I don't feel too bad about not following how the feedback related to what I was doing.

I'm just adding the MV and VVR to your IC removal mod from post 168. The 168 mod and a different speaker REALLY improved this amp. It's actually enjoyable to play now.

I was just digging though my various caps, pots and resistors and of course I don't have what I need so I'm gathering parts right now. I believe 1/2w on the resistors is all I need. On cap C1 there is an electrolytic there now, I really don't know when you use the various caps (elec, ceramic, poly, etc) over another in different applications. I assume I would use an electrolytic since that's what's there already, correct?

I'll post some pics when I finish, although I'm sure they will be embarrassing. I plan on putting the MV where the light is now and either drill a new hole for the VVR, or (I'm leaning toward) moving the switch and use that hole for the VVR.

Thanks for all your help.

[jim p]

I was just digging though my various caps, pots and resistors and of course I don't have what I need so I'm gathering parts right now. I believe 1/2w on the resistors is all I need. On cap C1 there is an electrolytic there now, I really don't know when you use the various caps (elec, ceramic, poly, etc) over another in different applications. I assume I would use an electrolytic since that's what's there already, correct?

On the wattage rating of the resistors the only one I know off hand that you need is R26 to a 25k you can just get by with a ½ watt there but a 1 watt would be better.

On the construction or type of capacitor film caps are your best then they vary by what they are made of Mylar, polyester, ect. problem being size and cost. You want your better capacitors in the signal path, the coupling capacitors such as C2 and C7. At the lower capacitance values mica caps are good ceramic capacitors capacitance value may change greatly with temperature and they can be microphonic. Electrolytic capacitors are usually just used for power supply filtering and at times if a large value is needed in a signal path such as the nopolar electrolytic capacitors used in crossover networks in speakers.

So if the capacitance value required is less than 1uF and the voltage rating is not too high you could probably find a film capacitor for that location.

Another thing about electrolytic capacitors is they can dry out so you should keep them away from the hotter components in the amplifier. I fixed a JVC TV and the basic cause of the failure was an electrolytic capacitor mounted inside of the u-shaped heat sink for the vertical deflection amplifier. Also good to keep high wattage resistors raised above the PCB for air flow.

[stoneattic]

On the wattage rating of the resistors the only one I know off hand that you need is R26 to a 25k you can just get by with a ½ watt there but a 1 watt would be better.

I also need a 1Meg resistor for the master volume, originally a 1/2 watt.

On the construction or type of capacitor film caps are your best then they vary by what they are made of Mylar, polyester, ect. problem being size and cost. You want your better capacitors in the signal path, the coupling capacitors such as C2 and C7. At the lower capacitance values mica caps are good ceramic capacitors capacitance value may change greatly with temperature and they can be microphonic. Electrolytic capacitors are usually just used for power supply filtering and at times if a large value is needed in a signal path such as the nopolar electrolytic capacitors used in crossover networks in speakers.

So if the capacitance value required is less than 1uF and the voltage rating is not too high you could probably find a film capacitor for that location.

I failed to mention that when I did your post 168 omp amp removal I didn't mod the tone control that you mentioned. I wanted to hear what just the omp amp removal sounded like. But now the tone control doesn't do much so I was going to replace C1 with a 200nf as you recommended. C1 is currently a 2.2uf (50v) electrolytic and after a quick check on mouser.com it looks like I might be limited to eletrolytics if I need the 50V.

So if cost it no object which order of film caps would you recommend?

Thanks again!

[jim p]

C1 has no more than two to three volts across it so you do not need a 50 volt capacitor there. A 6 volt or greater voltage rating will be fine. If you need the 1 Meg for R16 ½ or ¼ watt will be fine.

[SynySter_SlaSh]

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 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.

isnt the orange wire on r14 ?
I cant see anything on pin 6 of the op amp ???

Im confused, are there jumpers on the other side of the board ?

Do you have a picture please.

EDIT!!!

I have done the mod as to how i can see it on the photo, I put it back together just enough to test it but have a couple of concerns

1. with the plastic knobs off and a lead plugged in i was holding the guitar side of the lead with one hand and turning the vol pot with the other to test the signal, it seemed a bit noisy and as i turned it up i got a bit of a shock, i cant remember in which hand tho. i put it pack together and played through it a bit with a guitar. tone is definately improved and i am yet to change the bias resister to 180 ohms. although when i touch any metal part of the guitar there is a slight pop noise ??? sort of what you get on cheaper strats where the hum goes away from touching it, it wasnt there before the mod.

any idea what ive done wrong ? (shock, pop noise)

2. it appears that the tone knob goes from 0 - 5 (like a guitar tone control) and then doesnt realy do anything from 5 - 10

sugest me some easy improvements forthis please

thanks

[jim p]

isnt the orange wire on r14 ?
I cant see anything on pin 6 of the op amp ???

Im confused, are there jumpers on the other side of the board ?

Do you have a picture please.

EDIT!!!

I have done the mod as to how i can see it on the photo, I put it back together just enough to test it but have a couple of concerns

1. with the plastic knobs off and a lead plugged in i was holding the guitar side of the lead with one hand and turning the vol pot with the other to test the signal, it seemed a bit noisy and as i turned it up i got a bit of a shock, i cant remember in which hand tho. i put it pack together and played through it a bit with a guitar. tone is definately improved and i am yet to change the bias resister to 180 ohms. although when i touch any metal part of the guitar there is a slight pop noise ??? sort of what you get on cheaper strats where the hum goes away from touching it, it wasnt there before the mod.

any idea what ive done wrong ? (shock, pop noise)

2. it appears that the tone knob goes from 0 - 5 (like a guitar tone control) and then doesnt realy do anything from 5 - 10

sugest me some easy improvements forthis please

thanks

The orange jumper (pot to grid and input signal) in the picture is in the via (PCB hole) for R14 but if you look there is a PCB trace that ties that to the pin6 via of the op amp so it is the same as pin 6. So all the jumpers required for the modification are in the picture of post #168.

You can have more hum from line pickup (60Hz) because the bass response of the amplifier was rolled off at 250Hz by the values of C24 and R14 that were used by the op amp. If you touch the strings of the guitar and the hum stops that is a ground problem somewhere (usually the guitar).

Nothing in the modification changed the grounding of the amplifier and from the noise, pop and shock you are asking about a bad ground would be the likely cause. Have you reinstalled and tightened all the screws that hold the PC board into the chassis? Are you plugged into a three prong wall outlet that has a known good ground prong? Do you have florescent lights near by if so turn them off and see if noise stops?

As far as the tone control to get treble boost you will need to change C1 to a 200nF 6 volt or greater capacitor instead of the stock 2.2uF. The op amp provided treble boost before the tube stages without it you have no boost so tone control will only cut the treble.

Before you change R17 to 180 ohms you should read up on how to measure the power dissipation of a power tube in a single ended amplifier, it is probably in these posts and out on the web (how to bias a Valve Jr) for the Valve Jr (also a SE amplifier). You will need a voltmeter and have to make voltage measurements in the amplifier with it running. You have to be careful because you will measure the plate voltage which is approx 330 volts.

Hope this helps you figure things out.

[SynySter_SlaSh]

Thanks for all your answers guys.

Now juat wondering about this:

"Options:
Remove R7 for higher maximum signal on grid of second triode."

I what way will this effect the tone of the amp ?

thanks

EDIT

Im in the uk and cant seem to find a 6v 200nf cap, only the 50v big ones. suggest me somewhere online please ?

[jim p]

You can use a capacitor (or condenser) with a higher voltage rating it would be best to use a film cap and they usually are found in the lower voltage rating. As far as removing R7 it will only have an effect at a high volume setting and it is a little safer for the control grid of the triode to have it installed. Shorting R30 and R29 would be the better choice to increase the maximum signal into the second triode (but it will reduce the gain of the first triode). If you have plenty of range on the volume control as it is now I would just leave the volume control alone. Also I have noticed that some pots are touchy at the low setting and having R7 as a 220k should help. The way the volume pot is setup with the mod of post #168 is not the best way to go just easiest way to move the volume control to between the triodes. The volume control would be better to be a potentiometer and not a rheostat as it is in this mod. A rheostat is a variable resistor so the resistance the first triode is driving changes with the volume setting. If the volume control was set up as a potentiometer the second triode would be connected to the wiper so it is connected to a variable voltage divider. Then the first triode would see a close to constant load independent of the volume setting.
As a quick temporary capacitor change if you removed C25 in one piece it is a 100nF cap so you could replace C1 with that to get some treble boost starting at 1kHz instead of 500 Hz.
Also you could change R3 to two 750 ohm resistors in series then put 2.2 uf across one of the resistors and 100nF across the other for just +3db treble boost instead of +6db as you have with 200nf across the 1.5k stock R3. (see schematic) With the split resistor there is more low frequency gain.

[stoneattic]

jim_p,

Maybe I'm over thinking this, but I'm trying to decide on what capacitor to order to replace C1 and there a quite a few different types of film capacitors (polyester, polypropylene, metalized, etc). On top of that there seems to be few choices that have 200nf. I see plenty of 220nf, is that close enough?

Also, you suggested either 500K or 1M for the MV pot. What are the advantages/disadvantages between the two? Audio taper I assume?

Any specific type of resistor (metal, carbon, etc) for the 1 watt to replace R26?

Sorry for all the questions. I can handle the mechanical end of things (mounting, soldering, etc) but I'm just starting to learn the electronics end.

thanks

[jim p]

On the capacitor metalized polyester should be fine and 220nf is an OK value. Regarding R26 the composition is not that important it is just a series dropping resistor in the power supply circuit. On the tone front legend is that you would want carbon composition in the signal path.
The master volume pot needs to be an audio (log taper) pot with 1 Meg you will get a little more gain from the triode that is the input to the output pentode say by calculation 59 with 1 Meg and 57 with 500k ohms.

[SynySter_SlaSh]

hello again. which of these is most suitable for replacing c1

http://cgi.ebay.co.uk/4-X-MALLORY-0-2uF-600VDC-POLYESTER-FILM-CAPACITOR_W0QQitemZ350114259294QQcmdZViewItemQQptZ LH_DefaultDomain_0?hash=item51846fa15e&_trksid=p32 86.c0.m14&_trkparms=65%3A12|66%3A2|39%3A1|72%3A213 6|293%3A1|294%3A50

http://cgi.ebay.co.uk/5-pcs-MP-Axial-Capacitor-0-2uF-600V-10_W0QQitemZ140301844908QQcmdZViewItemQQptZLH_Defa ultDomain_0?hash=item20aaa441ac&_trksid=p3286.c0.m 14&_trkparms=65%3A12|66%3A2|39%3A1|72%3A2136|293%3 A1|294%3A50

http://cgi.ebay.co.uk/10-condos-polyester-mylar-0-2uF-200nF-200V-10_W0QQitemZ280348133654QQcmdZViewItemQQptZFR_YO_M aisonJardin_Bricolage_ElectroniqueComposants?hash= item41460d0916&_trksid=p3286.c0.m14&_trkparms=65%3 A12|66%3A2|39%3A1|72%3A2136|293%3A1|294%3A50

thanks

[rock_mumbles]

You could make any of them work...

(my opinion)

The third one would probably be the easiest to fit into the PCB I would expect it to be the smallest of the three caps and it has radial leads.

The second and third are probably both higher quality caps than the third one but installing them may be more difficult.

The second one with axial leads (leads come out of each end) has to be mounted vertically (staked) I used a Mallory 150 series cap for C1 in my V5.

The first cap "an Orange Drop" style had radial leads but is probably a much larger cap, the large Orange drops I've used have large diameter leads which can be difficult to install into the pcb

Here's a picture of my C1 "staked" cap

[jim p]

As stated in the previous post you can use any of the three, the first ones are large and usually used for coupling caps between tube stages. Also I surfed on electronic components at yahoo.uk where I go to see the latest on F1, The tour of France what Lady Ga Ga is up to, if Amy Winehouse has fallen into a pool in a drunken fit and also the swine flu status. Found there some distributors you can buy from RSH Electronics, Rapid Electronics and ESR Electronics are a few. Found a Web site for hobbyists Called The Electronics club they have a links page with distributors on it http://www.kpsec.freeuk.com/links.htm This one http://www.bowood-electronics.co.uk/ charges 1 Pound 65p for shipping with a minimum order of 5 Pounds. So instead of just caps for your shipping you could get some other parts you may need.

[rock_mumbles]

...
As a quick temporary capacitor change if you removed C25 in one piece it is a 100nF cap so you could replace C1 with that to get some treble boost starting at 1kHz instead of 500 Hz.
Also you could change R3 to two 750 ohm resistors in series then put 2.2 uf across one of the resistors and 100nF across the other for just +3db treble boost instead of +6db as you have with 200nf across the 1.5k stock R3. (see schematic) With the split resistor there is more low frequency gain.

Hi Jim, I just did this on my "Home Bake" (5F1 ???) scratch built amp and I really like it. I previously had a 1.5K cathode resistor bypassed with a 2uf film capacitor. With the split resistor treble boost the tone was evened out, it helped to tamed the (ugly) mid-range.

Thanks, for the great tip!!!!

[timothymegg]

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. 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.

I'm so happy !! I finally got around to getting a couple 100nf caps which I wired in parallel like you said replacing C1. The difference is night and day. Before the amp sounded too bassy and muffled without an eq in front of it. Now it sounds like a guitar amp again!

On another note: I re installed the R7 resistor to allow a little more headroom because the amp was breaking up too early. Now it starts to get a little crunch with hummbuckers around 4 and gets more driven from 6.5 on. Before it was breaking up as low as 2.5. So, I don't recommend taking out R7 in the mod I did in post # 240.

Thanks again to all the geeks and guitar amp freaks that put their knowledge out for adventurous guys like myself. Especially thanks to jim p and deafelectromark (manoteal) !!

Peace out!