Reg Edwards wrote:
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All power amplifiers have a tuned circuit in the plate. It is
essential to reduce output power contained in the harmonics.

In any case, power in the harmonics is wasted power.

With a tuned circuit in the plate it is impossible to achieve a
rectangular voltage output waveform. It is always a sinewaveform.

A rectangular plate current in conjunction with a tuned load always
causes harmonic power to be wasted at the plate.

So one might just as well use a sinusoidal driving waveform, Class-C
or not. It's easier. It also avoids generating and wasting harmonic
power in the driver.


Not true.

A network with an inductive input will allow a square waveform at the
device output but not waste significant energy in harmonics. I've done
that in designs.

In the 1950's RCA had an AM BC transmitter that drove a tube with a
near square wave, and had a near square wave. The RCA transmitter used
a low-mu triode that had parallel tuned circuits in the grid and anode
set at the third harmonic. It had conventional networks feeding the
grid and to the antenna from the plate resonantor. That transmitter
made over 95% anode efficiency.

73 Tom