John wrote:

Interesting idea, Johan, but I believe you'll find that if you drive the amplifiers with a sinewave, there is an efficiency penalty; whereas, if you drive them with a square wave, you actually have made a PWM modulator.

Yes and yes.

I meant square wave drive (class D).

My idea was to combine the modulator and the P.A. in the same stage.
This would eliminate the need for a separate PWM modulator in the
P.A. power supply.

The switching waveform will look a bit "spikey" at low output power. Worst case
is when the output power is close to zero, the signal will look like a train of 
impulses
with alternating polarity. I guess the spectrum will then contain all odd 
harmonics
at the same amplitude as the fundamental, limited only by the switching times.

Assuming a Q of 6 in the series resonant output circuit (typical value, I 
think), this
circuit alone would attenuate the 3f component by 24dB. Not too bad.


73
Johan SM6LKM