peavey deuce /low power problem

[mark allen]

amp will not turn up past 2 on master level. gets a more overdriven sound but not more volume. b version non vt series. tubes and speakers good.amp is way overdue for cap job but i need to know what is the most likely causes of this. all jacks and other controls work. amp has one master volume. sounds thinner over2.

[Enzo]

If both channels are similarly affected, then look first to the mixer amp stage, where the master volume is. Most likely in my mind? The 2uf/35v cap.

In fact I would suggest replacing every one of those. I would suspect them way before I;d worry about the e-caps in the power supply. There are at least 9 of them.

[mark allen]

thanks enzo, i will order some parts and let you know how it worked out. this is an excellent site. i have been on this site many times and should have registerd a long tme ago.

[mark allen]

enzo, i replaced all the caps on this deuce except the 4 power supply ones and the single 220uf which i am now going to order, from another place where im also getting new tubes. the amp is now working perfect again. thanks for your help.

[GridLeak]

Hello Everyone - New here to this forum. I do a lot of preamp building mostly for recording work but was asked recently to repair a guitar amp for a friend. The amp is a Peavey Deuce 240T.

The original problem was a weak PS filter cap and broken solder joint on the output stage cap/diode/OT CT connection. I fixed this problem and all seemed ok.

Two days later the amp was fired up and a new problem had arisen. The problem was pretty much the same as was described in the original post of this thread - output sounded very weak across all channels, volume would not increase when output was over 2 or 3 and the sound was mushy and more distorted than it should have been. The sound reminded me of what you would get if you used a variac and lowered the voltages to a near non working level. I checked the wall outlet voltages just in case and they were fine. I took the amp home and fired it up again before removing the chassis and same thing. After I removed the chassis I reconnected the speakers and fired it up once more and to my surprise the problem had disappeared - amp sounded normal again.

I've had it on the bench for a couple of days. All plate-screen and bias voltages are well within spec. I checked the 2.2/50V cap in the mixer amp as was suggested and it checked strong with a capacitance meter as did all the other 2.2s. I've tried to make it act up again via some poking and prodding around the output stage in case of a cold solder joint with no luck.

The good news is the amp is apparently working fine. The bad news is that whatever caused the output to get weak and mushy hasn't been identified and fixed - so I assume it will return at some point. I may just go ahead and change the caps in the mixer and driver stages though I would expect a bad cap to go once and stay 'gone'.

I thought I would post this here to see if anyone had any other suggestions, insight or tips as to how pinpoint the problem.

Thanks

[Enzo]

Hi, welcome. May I suggest starting a new thread for your amp instead of tacking onto the end of a dead thread. You will get better response, and there will be no confusing the two amps in the same thread.


Measuring the capacitance of those caps doesn;t tell you their health. Their ESR can go sky high, they can get leaky, upsetting DC levels in the circuit. And it has just been my experience over the years that those small value electrolytics used as couplers like this are often the cause of trouble. They are 35 years old after all.


Poke and prod the whole amp, not just the output stage. The whole circuit is involved putting sound out the speakers, not just the power stages. And a power stage problem would have no effect on the operation of a volume control.

Use a rubber mallet or your fist and whack the end of the chassis HARD. Does the amp react? It should not, but if it does, then there is a loose connection somewhere.

Places to look for solder cracks besides jacks - every control along the panel

[GridLeak]

Thanks Enzo,

I'll give it another go with some new caps.

Good call on the control panel PC mount pots. Forgot about those and I should know better - I've seen too many of them (joints) fracture on all types of gear.

[Enzo]

And while you are at it, check the controls themselves. Sometimes the wafer cracks.