[r8i0]

Bill, you've got a lot more experience than I do so I doubt I can help much, but I feel your pain.  I've got an 84B that has a similar volume jumping around problem that I've yet to diagnose.  I've prodded for loose components; looked for cold solder joints;  cleaned dirty pots and tube pins but haven't located

Good evening,
Earlier today I replaced the pair of 6f6 tubes with a pair of 6v6 tubes and the problem got worse. The bounce went crazy. Big highs and low lows. I am going to concentrate on the output for now and will report the results.
R8i0