Another Peavey Triumph 60 with problems.

[Inthe]

Here's the symptoms: It's way quieter than it should be with a weird clipping distortion when I run signal through the input or in to the return jack. This happens on all 3 channels. If I run a signal into the preamp output (which also goes to the power amp, effectively bypassing the preamp entirely) I get great,clean audio. This tells me that the problem is isolated to the preamp.

Here's what I've done:
Checked all the ribbon cables (they're good)
Reflowed all the tube socket joints
Checked heater voltages (they're good)
Tested all the preamp tubes (they're good)
Tightened all the preamp tube sockets.

The amp still malfunctions exactly as before. I don't have a scope, just a meter. Posting here is my last-gasp try before I send it to my tech. I know it has to be something simple and cheap. There's not more than $10 worth of parts on any of the boards in that thing.

[Chuck H]

If you have a scope and a signal tracer you can chase the problem down the signal chain. If you don't you can try the pop test by touching a metal probe (insulated handle!) to the tube grid pins and listen for the nature of the pop. This requires some intuition though since you do have some sound all the way to the input. Sooo...

Are any of the panel controls exhibiting unusual behavior? For example, do the tone knobs change the tone of the messed up signal? Do all the gain controls and master affect the signal level? Does wiggling any plugged in jack or knob make noise?

[Inthe]

If you have a scope and a signal tracer you can chase the problem down the signal chain. If you don't you can try the pop test by touching a metal probe (insulated handle!) to the tube grid pins and listen for the nature of the pop. This requires some intuition though since you do have some sound all the way to the input. Sooo...

Are any of the panel controls exhibiting unusual behavior? For example, do the tone knobs change the tone of the messed up signal? Do all the gain controls and master affect the signal level? Does wiggling any plugged in jack or knob make noise?

The jacks are cleaned and the controls do what they are supposed to.

[Chuck H]

If all the controls and switching is working as it should then plugging into the effects return with the guitar SHOULD yield a louder signal that plugging into the pre amp out jack. Since it doesn't that leaves only V4a and it's associated jacks and circuits in between. That's the effects loop recovery circuit. It's just a basic gain stage and a couple of jacks. One is a switching jack. There aren't any relays or pot controls. If you can trace a schematic and locate that circuit it's probably where you'll find a problem. I suspect something like a lifted pad on a jack mount or a sprung jack switch.