William E. Sabin wrote:
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.

Agreed.

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.

Thanks for that information. A related topic would be the effect of
tank circuit Q on the bandwidth of HF amplifiers; I seem to remember
reading something about, but don't recall what it implied about the
magnitude of the tube internal impedance, as compared with the load
impedance.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek