Barry got it! The OP states that "it is a solid amp" and I read that as "solid state amp"! My bad.
99% of issues with tube amps are tubes. I take it you have tried replacing tubes? The EL84s would be the first place I would look. Also, I recently watched a video by Psionic Audio on Youtube about servicing a Classic 30
. It was quite interesting. The filter caps are inexpensive IC brand and I would be changing those to F+Ts. The fella from Psionic really seems to know his stuff.
The way the circuit boards are connected looks like a recipe for disaster! Who ever thought that was a good idea??