[Amps] Two questioins about tetrode amplifiers.

[flynth at gmail.com]

Hi,

Could someone please confirm the output impedance of a classic tetrode
linear amplifier does'n change as plate voltage sags or swings?

I imagine it must be the same because no tetrode amp design I saw
stabilised the plate voltage. Then we also have a tuning switch that drops
plate voltage by half in a tetrode military amp many hams restore around
here . If output impedance changed by a lot it would make no sense to tune
with half the plate voltage

The second question is, has anyone figured out how to tune a tube amp
matching network with a nanoVNA? My tube is supposed to have an output
impedance of 2500ohms  so I tried removing it from the socket and replacing
it with a 2500ohm non inductive resistor then I tried to probe the output
port. I think this didn't show me the correct values.


Many thanks,
F.