[morzh]

Murf

If you are methodical in your approach you will easily get to the root cause.

1. Was it ever playing well?
2. If yes, were the tubes OK?
3. Whatever it was, are they OK now?
4. Have you changed EVERY cap (OK, forget micas).
5. Have you checked EVERY resistor? No point guessing "could it be a bad resistor", just check them.
6. Yes, voltages. But, if your tubes are good and your resistors are good, and your wiring is good, your voltages will likely be good too.

Start with the basics, that will likely give you your answer.