TSL 100 intermittent volume jump...?

[acorkos]

I saw this amp a couple of weeks ago....owner said it needed new tubes. It's an early one from 1999...I pulled the chassis and noticed the power tube grid resistors were 220K, so I replaced them w/5.6Ks, replaced all the tubes, adjusted the bias, spray cleaned all the jacks and sent it on its way...sounding good and apparently healthy. Owner calls back a couple of days later....says the amp sounds great, better than before, but still has an issue he forgot to tell me about (thinking it would be solved w/new tubes)...very intermittently, while playing, the volume jumps up pretty dramatically, louder than it should be, based on the volume control settings, and then after a couple of minutes drops back down. I had him insert/remove/reinsert a guitar cable plug in the input, effects loop and speaker jacks 20 times each jack, but he says the problem persists....Anyone heard of this before? Any help is greatly appreciated.

[52 Bill]

Bad pot, bad ground connection on the pot?

[Mick Bailey]

My thoughts too. Possibly a cracked joint on the ground side of a pot.

Incidentally, I always re-solder the bias boards on these. They're really bad for cracking the joints on the trimpot pins and losing bias. Amongst many other things......