Peavey Tube amp noise

[Alek Z]

About a year ago I was taking my peavey classic 50 410 reproduction out of the car, and without my noticing it had leaned up against the hatch and when I opened it, it fell out, hit the trailer hitch, and the my foot/the ground. Terrified, I ran to plug it in and it worked fine! So I thought...
Playing it again later I noticed a strange kind of scratchy poppy noise, but only after playing the amp for 5-10 minutes. Being a tube amp I just figured I’d screwed up one of the tubes, and having way too many of every tube laying around I just popped a whole new set in, and the noises persisted. I acquired a Marshall shortly after this so I stopped playing at let it set for 6-8 months saying I’d take a look at it one day, hopefully there’s an obvious fix, since I have some knowledge of amp repair. I looked inside and just decided to do some research instead to find a quicker solution. Though a strange development happened since I’d let it sit for so long, now after playing for about 30 minutes (noises still hold off at first) it just started shrieking and I don’t know how to explain the sound but I had to immediately turn it off. Any help would be greatly appreciated because I’m fairly clueless.

[Enzo]

The amp fell. Something has been knocked loose. SOMETIMES it can be visually obvious, but usually not. So we use something insulated, like a wooden chopstick, and poke at each component to see if we can find something that reacts. Could be nothing more than a cracked solder joint.


What does reproduction mean? Peavey made a Classic back in the 1970s. They also made a Classic 50 in recent years. The latter is not a reproduction of the former. Are there newer still models?

[Chuck H]

The time sitting can mean oxide on any contacts that aren't soldered. Tube socket holes, switching jacks, ribbon contacts etc. DO CLEAN such contacts and then make further assessment of the former problem. As Enzo mentioned, it's probable something was knocked loose. This could be anything. Rid the matter of any complications from the amp sitting and oxidizing and then reboot the matter.

[glebert]

I would try to narrow it down to preamp or poweramp. Since you have a master volume if you turn that down does the noise go away? If so it is in the preamp, and you can see if any of channel controls change the sound. That can help narrow down where the problem is. If the noise doesn't go away it is in your power amp, V3, or the effects loop jacks/sub board/ribbon cable. There are a number of cables that connect parts of the amp together, such as the feedback, I would check those to see if something is half-loose.

By reproduction I am guessing one of the later ones with the oval badge on the front? I think they moved production to China somewhere in there. Mine is a later one as well.

Here is the schematic: https://www.thetubestore.com/lib/the...-Schematic.pdf

[Alek Z]

Yes the reproduction just meant the later model, it's in a 410 cab and has the classic yellow/brown material on the outside, but definitely newer due to the electrical components, my apologies for the confusion on that. Thanks for your responses, I'll check around for loose components, and use some contact cleaner. I haven't actually played the amp in a while, and I recall I did do a diagnostic of the pre amp vs power amp in the fashion mentioned and I think it's in the pre amp? I don't remember exactly, it's a fairly hard problem to pin down due to the infrequency of the noises actually occurring, just in that it's not a constant noise, but does happen every time I use it. I'll do cleaning tonight, then do the diagnostics.

Enzo - when you talk about poking at things with a chopstick to see if they react, how would they be reacting? What should I look for while doing this?

[Enzo]

I poke with a stick to see if anything reacts. If it reacts, it is loose. Well soldered parts won't react.

What does react mean? I means just that - the part reacts to touch in some fashion. Usually by making a noise.

[Alek Z]

Ok, so do you have the amp on when you do that and the noise will come through the speaker when you poke it? Or would you have it off and you hear it rattling in the joint?

[nevetslab]

Ok, so do you have the amp on when you do that and the noise will come through the speaker when you poke it? Or would you have it off and you hear it rattling in the joint?

The amp is powered on, speaker connected. If you were able to narrow the issues down to preamp section or power amp section, and can find that area on the PCB, then you would poke/prod with the chop stick, like tapping on the top of a resistor, capacitor, diode and such. Not enough to break a lead, of course. If a part reacts enough to scare you, you probably have found a broken solder joint. It helps having high intensity light on the area you're prodding. Tapping on the tubes is another method similar to prodding with the chop stick. If you found a tube that reacts strongly to that, you may have tube contact issues. Often one can re-tension the tube socket contacts, though that is only done with power off, all power supply caps fully discharged, and AC mains cord disconnected.