As a curiosity, since Marshall used the U/L operation to get 200W from 4 KT88's running in push-pull in its famous Major amp, I just wonder how much power can be squeezed out of two of them operating in class A in U/L mode. I'm thinking (and maybe with little acknowledgement of the tubes needing to "rest" once in a while...) that if you can get nominally the rated dissipation of plate and screen as your output power for class AB operation, it shouldn't be impossible to get half that for class A? And, if not, how close can you get before the onset of cut-off or grid loading?
With all losses calculated in, you should be able to squeeze an honest 40W output from 1 pair in class A UL PP. 2 pairs (4 tubes) should give 80W.
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