That's a cool old vintage amplifier!
I can imagine that a lot of the electrolytic capacitors have gone bad, that's pretty common in old tube amps. There may be a few resistors that have gone out of tolerance also, usually the plate resistors on the tubes drift out due to the heat in use if the amp is pushed regularly. They seldom fail, but they can go out of tolerance.
Do you have a schematic for the amp?