"Walter Maxwell" wrote
What seems to be overlooked here is that the source resistance at the
output
terminals of the pi-nework in Class B and C amplifiers is non-dissipative,
which
is the reason they can be loaded for delivering all available power for a
given
grid drive, and still have efficiencies greater than 50 percent. One of
the
myths circulated for years, and still prevelant, is that the reason for
Class B
and C amps to have efficiencies greater than 50 percent is that the load
resistance must be greater than the source resistance. Tain't so.
____________

Walt - what is your thinking on the point that untuned, solid-state
amplifiers also can have PA DC-to-RF power conversion efficiencies of 70% or
more at the device level?

In fact the solid-state, analog FM broadcast transmitters supplied by Harris
Corporation and others need no tuning to produce their rated output power
into a 1.3:1 SWR or less, anywhere in the FM broadcast band 88-108 MHz.
Even the harmonic filter needs no changes, and maintains harmonics at -80
dBc or better. They are frequency agile, and can be reset from one carrier
frequency to another, anywhere in the FM band with a transition time of a
few seconds

The overall AC input to r-f output efficiency of these transmitters exceeds
60% (includes the exciter, control system, IPA, and cabinet fans).

RF