Recently we serviced a Guyaton amplifier having an overheated output power tube 6L6GC and after extensive troubleshooting we found the problem was in the bias section of the power tube.
The tube was running at approximately 300% of the recommended plate dissipation due to faulty decoupling capacitors. Later on, we realized that all the high voltage electrolytic capacitors had problems causing not just the damage of the power tube, but additionally tremolo malfunction and noisy signal
Vintage Amp Repair 