Can I troubleshoot my own amp?

[zionstrat]

Hey guys, our incredible amp technician has retired and there's no other competent folks in the area. I need to sell my Peavey50 classic however it's developing the crunchy static thing that happens when an old amp warms up. The hotter it is the more crunchy static you get.

From past experience, I hear that this is likely a capacitor that is going or is losing its connection And I'm wondering if this is something that I can troubleshoot?

Although I do tons of guitar wiring, I've always avoided AC because I know there's big capacitors in there that can kill you. For me to be successful, I think I need a how to list, to safely discharge capacitors and then go through components. I can follow schematics but it's all plumbing to me.. I can see the path but I don't know what I should understand about the electronics themselves.

I'm good with a multimeter for resistance and it's got a hundred other settings on it that I don't use :-)
This isn't something that I expect to do in the future so an extremely simple idiots guide would be useful.

Do you guys think this is doable and can anyone point me to content?

Thanks either way, Michael

[Demanic]

You are correct in that you have to be certain of the caps and how to safely discharge them. 500VDC can really ruin your day.

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[beaubrummels]

If you are that new and uncertain, I would find a competent repair shop that is not local and send it out.

If you are doing your homework and feel you can get through it, you'd know there isn't an idiot's guide. You either know exactly what you need to do and fix it right, or you don't.

[Demanic]

If you are that new and uncertain, I would find a competent repair shop that is not local and send it out.

If you are doing your homework and feel you can get through it, you'd know there isn't an idiot's guide. You either know exactly what you need to do and fix it right, or you don't.

Yeah, just like with any other dangerous tool, idiots and amp repair don't tend to mix well.
The only upside is that you really only get to make one serious mistake.

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[zionstrat]

Okay, sounds like you guys have got me looking for a tech in another city :-) much appreciated!

[Ewizard]

The short answer is no you can't; the long answer is that you most certainly can..... If you accept the challenge and responsibility of bricking the thing.

You can do what is known as shotgunning, where you simply replace all of one type of part, in hopes that you get it. Or you can do the more technical method of trying to nail down where the problem is coming from and replace parts around the problem area/s. The latter is where knowledge is power. Generally, you can nail down noise issues by simply removing a tube and seeing if things improve. You start with V1 and move toward the power tubes removing only one tube at a time. If you're lucky, when you remove a tube and the noise goes away, you can isolate it to that tube's circuitry. You can replace teh components directly related to that part of the circuit and hopefully, the problem goes away. You also try and replace the "noisy " tube with a known good one, just to ensure it is not the tube that is the issue. If you remove all the tubes from the input to just before the output tubes, you have an issue in the power supply that is manifesting in the output.

Resistors are also known to cause crackling, especially on the preamps plates. But it can happen as well with bypass caps on the cathodes. The short answer is that it is not that easy to simply prescribe a particular problem. I had an issue once where I was certain it was a bad Plate resistor, nope, it was a bad tube.

I think it would be best and more prudent for you to find even an average tech. One that can make a living at all fixing guitar amps should be good enough to at least make the amp work again without noise. Price-wise, well, good techs aren't cheap and cheap techs aren't good.

[zionstrat]

The short answer is no you can't; the long answer is that you most certainly can..... If you accept the challenge and responsibility of bricking the thing.

You can do what is known as shotgunning, where you simply replace all of one type of part, in hopes that you get it. Or you can do the more technical method of trying to nail down where the problem is coming from and replace parts around the problem area/s. The latter is where knowledge is power. Generally, you can nail down noise issues by simply removing a tube and seeing if things improve. You start with V1 and move toward the power tubes removing only one tube at a time. If you're lucky, when you remove a tube and the noise goes away, you can isolate it to that tube's circuitry. You can replace teh components directly related to that part of the circuit and hopefully, the problem goes away. You also try and replace the "noisy " tube with a known good one, just to ensure it is not the tube that is the issue. If you remove all the tubes from the input to just before the output tubes, you have an issue in the power supply that is manifesting in the output.

Resistors are also known to cause crackling, especially on the preamps plates. But it can happen as well with bypass caps on the cathodes. The short answer is that it is not that easy to simply prescribe a particular problem. I had an issue once where I was certain it was a bad Plate resistor, nope, it was a bad tube.

I think it would be best and more prudent for you to find even an average tech. One that can make a living at all fixing guitar amps should be good enough to at least make the amp work again without noise. Price-wise, well, good techs aren't cheap and cheap techs aren't good.

Thanks for a great summary! As much as I love modifying guitars and all the theory that goes with it, I can't imagine that there is much of an amp modding market in this area, so probably no good reason for me to learn the skill set.


Thanks again!