> if you set your quiescent current at 100% of plate dissipation in a Class A amp then apply maximum signal for full volume, you will drive the plates over their power dissipation rating and they may red plate.
No. A class A amp runs *cooler* when you work it HARD.
This was only theoretical until I ran an older tube into dummy load. It creaked when it got hotter or cooler. Going zero to max, I could hear the cooling creak. Simple metering confirmed the DC power hardly changed while the dummy resistor was smoking its paint. IR probe confirm the plate ran cooler at full sine, even cooler pushed to hard clipping.
> couldn't work out how zero-signal plate current being 72mA and maximum-signal plate current at 79mA
That sounds like a push-pull condition.
72mA per _pair_ is 36mA each. At idle, a steady 36mA. Under large signal, one side swings down to zero and up to 72mA, the other side swings up to 72mA and down to zero.
It is a see-saw on a stump. Idle, both sides level above the ground. Under children, one side goes to zero (hits the dirt) and the other side goes twice as high.
> 72mA ... 79mA
Perfection would be 72mA. Tubes are curved. The "79mA" is a DC reading and not the peak. Tubes turn-on better than they turn-off, so under heavy signal they tend to conduct a bit more.
No. A class A amp runs *cooler* when you work it HARD.
This was only theoretical until I ran an older tube into dummy load. It creaked when it got hotter or cooler. Going zero to max, I could hear the cooling creak. Simple metering confirmed the DC power hardly changed while the dummy resistor was smoking its paint. IR probe confirm the plate ran cooler at full sine, even cooler pushed to hard clipping.
> couldn't work out how zero-signal plate current being 72mA and maximum-signal plate current at 79mA
That sounds like a push-pull condition.
72mA per _pair_ is 36mA each. At idle, a steady 36mA. Under large signal, one side swings down to zero and up to 72mA, the other side swings up to 72mA and down to zero.
It is a see-saw on a stump. Idle, both sides level above the ground. Under children, one side goes to zero (hits the dirt) and the other side goes twice as high.
> 72mA ... 79mA
Perfection would be 72mA. Tubes are curved. The "79mA" is a DC reading and not the peak. Tubes turn-on better than they turn-off, so under heavy signal they tend to conduct a bit more.
It's actually the spec's for SE operation. See Load lines and manufacturers figures (newbie)
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