Tube Amp Archive

Put a bright-cap, say 100-300pF depending on how much brightness, across the Drive-volume, from signal in to wiper. That should bring back alot of harmonics the that muddy drive. Normally, I'm not too happy with brightcaps all over the place, but here it does the job.

Could be bad resistors, possibly the plateresistors, or soldering, since it happens when the amp has heaten up. Could also be small current traveling between the boards, common in old dirty amps that's been sucking up fluids for many years.

Hey buddy, if it's the fs5 schem you need, I've got it.
I do warrantyrepairs on Koch-amps in Denmark, I might be able to help you. I'll have to get clearence if I can post schematics from Koch, have never signed a nondisclaimer from them although I got all schems from them.

cheers