I agree with Rockvirgo. I don't think the caps have anything to do with it.
Amps with no global negative feedback have no choice but to let the bias drift. Without feedback, thermal changes cause an imbalance in the bias and that imbalance grows with temperature and time. Pass amps are known for needing to have the bias readjusted every so often to account for the average increase but maybe after a few days of being left on, it can peak and run the transistors out of headroom. I knew a guy who readjusted the bias on his X350 every few months, for example.
PS, I think the bias is class A at first in some amps due to current inrush and not deliberate design. See JA's measurements for high bias amplifiers and you can see this effect. One of my buddys has a Gryphon ST-100 amplifier that will burn the skin off your hands the first half hour after turn on.
Arthur
Amps with no global negative feedback have no choice but to let the bias drift. Without feedback, thermal changes cause an imbalance in the bias and that imbalance grows with temperature and time. Pass amps are known for needing to have the bias readjusted every so often to account for the average increase but maybe after a few days of being left on, it can peak and run the transistors out of headroom. I knew a guy who readjusted the bias on his X350 every few months, for example.
PS, I think the bias is class A at first in some amps due to current inrush and not deliberate design. See JA's measurements for high bias amplifiers and you can see this effect. One of my buddys has a Gryphon ST-100 amplifier that will burn the skin off your hands the first half hour after turn on.
Arthur