Noob Q: are the efficiency figures for valve amps the same as with transistors?

[mr_push_pull]

Yet another newbie question. A friend of mine that's even less knowlegeable than me about tubes wants to buy this 6x200W Yamaha valve amp and this raised a good question: what are the efficiency figures for valve amps? What's the rough relationship between the class of operation and efficiency?

 

[Sch3mat1c]

Theoretically, class A goes from 10 to 33 to 50% efficiency (I think). Class AB runs from that to 66% or so, at class B. Class C is better at 66 to 80%, with extreme cases as class D running to 90 and 95%.

Class C is useless for audio unless modulated; class D is typically PWM.

All classes apply to both tubes and SS, but because SS has lower saturation voltage and no screen and heater power to waste, it always caps closer to theoretical maximums.

Tim

 

[mr_push_pull]

Class D with valves? Has it been done?

 

[Frank Berry]

"Class D with valves? Has it been done?"

Yes. In some amplitude modulated transmitters.
Harris called it PDM. Pulse Duration Modulation.

 

[Sch3mat1c]

I'll have to experiment with it someday, too. Will be interesting keeping it right on the knee so the screen doesn't melt.

Tim