[Phlogiston]

Question for you tube amp gurus:  A bit of background before the question. Normal suggested bias for the 7591A pair is 70ma combined cathode current (35ma/tube). The amp generated fair heat and the trannies would get fairly warm to the touch.  Reduced current to 65ma and noticed a reduced heat factor, without affecting the sound - plenty of power in my studio.  I've now reduced the cathode current to 56 ma (required a bit of circuit change to get the bias voltage where it needed to be for the reduced current), and the amp still sounds great, though I'm sure my max power output is down, but still way more than I need.  How far can one reduce idle current before a degradation in sound at lower listening levels?  I would assume that getting the current too low would put the tube in an operating range where linearity would be affected.  I'm just looking for maximum tube life without sacrificing sound quality.  Power supply voltages run about 15 volts high with the reduced output idle current.  A problem? Well within the voltage ratings of all caps.

I think nobody answered the bias question because it is hard to tell. At some point the sound becomes a bit thin and tinny. A little depends on the listener. I don't think what you have done will be noticed.

As to the B+, how does it compare with the max plate/screen voltage of your output tubes?

Yeah, add a fan.