1971 traynor ygm3 risen from the dead, dying again

[otthedevil]

so my buddy found this in a dumpster and brought it to me, i gave him $20 for it. i plugged it in and it works just fine for an hour or two, then cuts out, no sound at all(all 3 inputshave the same result). I took it apart, cleaned up everything, and changed out one of the 12ax7 sockets, because it was arcing to the chassis. this worked great. Reverb was good, trem was good, nice and clean to nice and dirty at volume 3. I took it to grandma's and plugged in, and now there's barely any sound. i get a real distorted whisper, but its intermittent like, not consistent. Inside, all the connections look good, I dont find any questionable components. I jiggled the tubes and rotated them , no change.
Whats a good place to start?I figure to replce all the tubes, these gotta be 20 years old. all the pots did their job before , now none of them have any effect on the output sound. please advise

[vavlehead]

try another speaker for starters. and then the power tubes.

[otthedevil]

if it were a speaker issue, wouldnt the pots effect the sound?i'll check it out when i get home.