Tuning is VERY touchy. You really have to have the loading right or the screen
current is
excessive in either direction.
None of my 4CX1000A or 4CX1500B amps were all that touchy, from 1.8
to 144 MHz. Screen current does vary with loading, from negative
through zero to positive, but it is a smooth and easily controlled
change provided the loading capacitor has some reasonable rate of
adjustment. I prefer vacuum variables, but if using an air variable
I put a vernier drive on it.
With vacuum variable tune and load caps in a pi network, I have no
problem going from band to band by using logged presets. Of course
the presets have to be changed if I make any change to the antenna
system, and tuning needs to be verified if there is any possibility
of weather conditions affecting the antenna (ice or snow).
73,
Paul N1BUG
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