Hi Mike, in answer to cold tuning the output network:
The tube contributes a significant part of the total C1 value; for this
reason, it needs to be in the circuit. If this causes a problem connecting your
load resistor, the resistor can be placed across the rf choke with nearly the
same results, especially on the bands between 160 and 20m,
C1 resonates the network and C2 adjusts the output impedance. Therefore, in
your cold test C2 should be used to provide 50 ohms output. C1 resonates the
network and you should be able to remove or null the reactance reading showing
on your bridge. There is some interaction between C1 and C2 but the network
should act as described. Said another way, C1 will also change the 50 ohm
reading but not as much as C2, C2 will change the resonance/reactance but not
as much as C1
The method you are using is a wise move to confirm all is as expected. I
have used this method as high as 432 MHz with good results.
Happy tuning!
73,
Gerald K5GW
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