@glyph @adhdeanasl The gain structure on my #1 guitar amp is notoriously finicky, in part because the two channels feed each other, both are extremely sensitive to input variation, both respond to a “jazz/rock” master toggle, all three EQ knobs have extra toggle switches and THEY all interact with everything else in non-obvious ways, plus I have had it modded with a A/AB power switch and a 3 way toggle to pull negative feedback from different points in the internal signal chain.
ANYWAY I managed to get it set up sounding like absolute ass last summer, thin, raspy, no mojo whatsoever, went down the rabbit hole of tube swapping with little positive effect, and have been disappointed with the sound ever since.
I finally sat down with it, left the tubes alone, and dialed everything up from scratch…I do this by turning up the final master volume to max, nothing plugged in, and moving every knob and toggle while listening for variations in the low level hum/noise of the output (hat tip Steve Kimock who mentioned this trick on a message board decades ago). I listen for inflection points; spots on the potentiometer range where an audible change occurs. If you can hear that, you can trigger it with your picking hand, which is what I want from this amp. Maximum touch sensitivity.
It took about 90 minutes but I solved it using only my ears and more patience than I was able to muster over the last 6 months. It sings again. When the amp is dialed, I play more often, I play differently, and I enjoy it more. Winning!