[Amps] Help with ARRL handbook design 4CX1000A 2m PA

Pete Lindsay psl at plcg.org
Mon Jul 21 12:43:27 EDT 2008


Hi Guys,

I have a 2m PA built around the design in the 1986 ARRL handbook
chapter 31 using a 4CX1000A. It was built by a friend to a very high
spec and looks like an exact copy of the original design. The problem
is it has never really worked that well. The problem lies in the
output efficiency which, at best, is only around 30-35%. I am using
3KV on the anode and have tried several tubes. The screen grid and
control grid currents act as you would expect when
increasing/decreasing the loading, but the output is just not there
(measured on several different power meters). I would be very
interested if anyone out there has successfully built one of these
amps and managed to get a reasonable output efficiency. Other amps I
have built with 8877/GS35 etc all work fine, but this one has me beat.
Is there a critical part to the design which needs close attention to
get it to work? Any help appreciated!

Thanks


Pete, G4CLA.


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