W3JDR wrote:

In order to get any semblence of efficiency, the drive waveform should drive
the stage from near-cut-off to near-saturation, somewhat like a switch.
However, depending on how hard the sinusoidal input signal drives the "Clacc
C" stage, the conduction-angle and thus the duty-cycle of the output (before
filtering) will increase or decrease, resulting in variable output power in
the load.

Joe
W3JDR


Who said the drive had to be sinusoidal? If the final can run almost square
wave, why can't the driver?