Crackeling Peavey Classic 50/50

[hj5150]

List,

A while back while rehearsing, my amp decides to start making a crackling sound. The crackling sounds like a bad guitar cord. Thinking I may have a bad cord, I change my guitar cord but the crackling remains. I lightly tap on the amp and the crackling fluctuates with every tap.

I bought the amp used, and have no idea of its history, so I decided to change all the tubes. I changed the "Peavey" brand tubes with a complete set from EuroTubes. Thinking my problem is solved, I go along my merry way. Well as my fortune has it, the crackling comes back. I gave my amp to a fellow "electronics hobbyist" for the weekend. I tell him the crackling is very intermittent. He gives it back saying it never made any unusual noises for him. Last night we are rehearsing, and after the first hour I put the amp on standby. After a 20 min break I take it off of standby and it immediately starts its very annoying crackling sounds. I do some troubleshooting:

I unplug my guitar input to it so there is nothing going in, still cracks.
Lightly taping the top cover, the crackling is affected by every tap.
While I use a screwdriver to remove the screws on the top plate, the crackling sounds are being affected by the turn of the screws and the removal of the top cover. - It still cracks.
I switch the ground switch on the back of the amp to all positions, it still cracks.
I lightly tap on the plate that houses the tubes in the center of the amp, and every tap affects the crackling. Still continues to crack.
I decide to change the speaker cable to my cabinet - still cracks.
I plug the cabinet into a different speaker output - still cracks.
I lightly tap each of the 4 large capacitors that lay horizontal near the center of the board. The left 2 make no difference in the crackling sound. The right 2 affect the crackling sound with every tap, as well as the black vertical capacitor.

Taping on the transformers do nothing to the crackling sound.
Plugging the amp into a different wall outlet, or in 3 separate houses for that matter do nothing to cure the crackling.

I'm really trying to say "No to crack", but I'm at my wits end. And suggestions are more than welcome.

Thanks in advance

[BiBi]

Definitely not an expert here but when I've had crackling it usually means a bad solder connection somewhere. It doesn't sound like you are so comfortable using a soldering iron but if you are discharge the caps and go over all the connections. Is the Peavey on a circuit board? If so they usually have the most issues with heat and the like.

Also on another note, don't leave your amp on standby for long periods of time it actually will burn out your valves faster.

[hj5150]

OK, did some more research. I pulled the boards and checked for faulty solders. Nothing. Reseated all the tubes and connector plugs. Put it all back together and let it run for an hour (not on standby. . . thanks for the tip). Started crackling again so I did some more testing. Here are the results:

Put the amp in stereo mode. Each channel works perfectly. Clean and no static/crackling.

Switch the selector to mono (bridged or bi-amp mode?) and it starts crackling.

In mono with left channel on, right channel on = crackling.
In mono with left channel on, right channel off = crackling
In mono with left channel off, right channel on = perfect!

It appears that as long as the amp is in mono mode with the left channel on, it cracks.
If I’m in stereo mode, either the left or right channel independently sound perfect.

Thoughts?
Could it be my mono/stereo selector switch?

Thanks again.

[BiBi]

Hi again. Yes it sounds strange. How did you check for faulty solder joints?
Most of the times they are very difficult to see. But if you are patient and careful (especially on PCBs) you can reheat the solder connections. Yes it is a pain, but if it fixes the problem you're in luck.
Have you already switched around the valves? Just a guess but try exchanging the PI valves between channels, or better yet try some new ones. Then, try the output valves.
Good luck!

[hj5150]

Hi again. Yes it sounds strange. How did you check for faulty solder joints?
Most of the times they are very difficult to see. But if you are patient and careful (especially on PCBs) you can reheat the solder connections. Yes it is a pain, but if it fixes the problem you're in luck.
Have you already switched around the valves? Just a guess but try exchanging the PI valves between channels, or better yet try some new ones. Then, try the output valves.
Good luck!

I checked the solder joints with a magnifying glass. They all looked to be clean and complete.

Valves, I have never heard the term valves in an amp. I'm not that savvy. If you are referring to the tubes, yes, they have been pulled and replaced in different sockets.

Thanks again.

[Enzo]

SO squirt some cleaner in the mono/stereo switch.

[hj5150]

SO squirt some cleaner in the mono/stereo switch.

Good call. Never even thought of doing that.
Bought some cleaner yesterday and used it. Sadly it didn't work.

Grrrrrrrrr.