Ian White, G3SEK wrote:


* The output impedance of the transistor doesn't come into the story at
all - not when characterizing RF power devices that are not operating in
class A. Even the device manufacturer doesn't know or care what it is.
Neither need we.



Tubes and transistor power amplifiers quite oftem
use negative feedback to improve SSB linearity.
Improvements of 5 to 10 dB are common. The
negative feedback reduces the internal impedance
of the tube and transistor amplifiers. The
tube/transistor data sheets do not consider this
factor.

Again, we usually don't really know or care much
about the values of the internal impedances.

But there is a special case. Voice/music/data tube
transmitters operating at low frequencies have a
problem called "sideband clipping" where the plate
tank selectivity may be too sharp and reduces the
modulation bandwidth. The internal impedance tends
to broaden the response at resonance. When
designing the tank circuit this effect may have to
be included.

Bill W0IYH