Richard Fry wrote:
"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

I know this question was directed to Walt, but I'd like to mention that
I've designed and built solid state class C amplifiers at the 5 - 10
watt level which have measured efficiencies of greater than 85%.

Roy Lewallen, W7EL