Buzzing sound but no sound from guitar.

[jamowil]

I have an old Peavey Classic hybrid amp, 50 watt, tube power amp, SS pre. When you switch the amp on all that happens is a temendous amount of hiss comes out. I've tried moving all of the knobs, but nothing happens what so ever. When you plug in a guitar cord there is a pop from it getting plugged in, but no input sound. I am very confused and would love it if someone could shed some light on the situation.

[Enzo]

Do you have a plain old Classic? Or is there a "VT series" or "VTX series" inder the Classic name?

The VT and VTX have power amp in jacks. And if you have that, plug a guitar into the power amp in jack. Any change? And you can run a cord from Preamp out jack to some other amp to see what the preamp section sounds like.

The original Classic came in A and B versions. The A had four input jacks - two normal and two bright. The B version also had four input jacks, but it was one bright, one normal, a series, and a parallel. But they lack power amp jacks and preamp out jacks, so we can't look there.

What it sounds like to me is a noisy/failed transistor. Or conceivably a missing power sipply voltage. This is going to require taking the board out of the amp and soldering parts on it. We will also need to check voltages here and there. If this is not in your skill set, then the amp will need to go to your terchnician for service.

[jamowil]

This is a plain old classic, A version. I don't have much experience in this type of stuff but I'm willing to try my hand and do my best to learn as much as possible. How would i go about finding a failed transistor? just take a voltage meter and test everything out until one of them doesn't check out?

[Enzo]

Sorta. I'd go through the circuit comparing voltages I find to those on the schematic. I'd apply a steady signal to the input, and trace it stage by stage through the amp to see where it disappears.

And I'd expect to replace ALL those small value electrolytics in the signal path.

[jamowil]

Ok, we have improvement. I don't know what happened but it sort of works now. The sound comes through when you have the channel volume dimed and the master 3/4 of the way. However the sound is fuzzy and if you pick lightly or turn the volume on the guitar down nothing comes out. I have tried it with two different speakers and a guitar and cord I know are good. Would it be a faulty volume pot or old tubes? they still heat up and get bright. And thank you so much for the help. I really appreciate it.

[Enzo]

My last line in post #4 is what I think it might be.

[jamowil]

Ok, I think I'm in a little over my head. How much do you think it would be to get it fixed? I only have about $25 into the amp as is so I'm ok with abandoning the project if that's what it comes to. I don't know much about the amp and I got it broken so I don't have any real attachment to it. If it's worth it I'll stick with it but if not that's fine

[Enzo]

You'd have to ask your local techs about their rates.

Here in my shop, something like that would likely not take over an hour and a half, so $60-90 labor. Parts are probably not going to be much. All those little caps are maybe a dollar each on a repair bill, likewise the small transistors in the preamp. Now whether it is worht it to you is up to you. It is a very rare Peavey amp we can't get back to working perfectly.

[jamowil]

Is it really that rare of an amp?

[Enzo]

Sorry if I was unclear. I meant it is extremely rare that we cannot repair a Peavey amplifier. Peavey amps are well supported, always have schematics available, have parts available, are well built, and mostly convenient to work on.

[jamowil]

Oh ok, well thank you very much for all the help. I really appreciate it.

[kurtdaniel]

Sounds like a ground loop in your system. Usually solved by checking your power cables for twists, tangles, and conflicts in your outlets. Thats what i learned from my advance guitar lesson..