Hi,
I am happy to accept that the 4CX250B family have their limitations, I run a
conduction cooled version (CCS1) on 2m. Sometime I will post my screen
regulator circuit somewhere for a reference. It consists of a simple
constant current source feeding a shunt regulator, with some other
protection incorporated.
My grid circuit is heavily swamped, partly to reduce the overall gain of the
amplifier as I have a surplus of drive power available.
Interestingly a few veterans of 2m SSB have actually taken the time to give
very positive reports, one in fact said "if you hadn't told me I would have
never have believed that you were running a tetrode".
During one SSB contest I suddenly got a bad report from a local, I was
beaming right through his location and operating very close in frequency,
since he is a "serious contester" I quietly slipped away and went QRT. Away
from the contest I found myself questioning what had gone wrong... too much
drive.. too little idle current etc.
Went through loads of permutations before I found the villain of the piece
was the processor in the driving rig!
In conclusion I am not suggesting for one minute we should not be seeking
low distortion in our PAs but it is somewhat critical of clean drive!
Regards David G0FVT
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