[Rainer.]

Yep, completely sure. The drive channel works perfectly fine, it must be the amp...

Another piece of the puzzle has emerged. When the amp is having one of it's tantrums (as I am calling them now), when set to the clean channel, the drive channel's master volume actually makes some sound louder and softer, none of the other knobs on the drive channel work on the clean channel, as expected, except the master volume, which seems to be having some effect while the clean channel volume doesn't cut out all the sound when all the way down.

This makes me think it probably is the channel switching, then, like you said MT.

So is it shop time?

[BillSPrestonEsq]

dumb question, but what about a dead pot on the clean channel? I had a dud pot in my old crate that sounded exactly like your clip. I am not sure how the t-50c is set up exactly, but a bum pot would seem to explain the sound bleeding through when all the way down. Thats just a guess, but it seems to match the problem to me.

(is the master volume a master volume or a post volume control on just the crunch channel?)

[Rainer.]

Post volume on the dirt channel.

All the pots on the clean channel are working when the whole clean channel is working, plus I've tried wobbling them around, and so It's not a bad joint on any of 'em. So I'm thinking relay switch.