To do the test with the resistor and the VNA, you should leave the tube
in place, since the output capacitance is important. Of course you must
disconnect plate and screen supplies.
73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco
On 31/10/2024 8:37, flynth@gmail.com wrote:
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.
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