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

[Peter Voelpel]

I built with those tubes a push-pull 2m amp many years ago, it was a
quick&dirty design with efficiency at 58%.
So the tubes do very well there. 
Is there something running hot in the output circuitry? Capacitors,
stripline, coil etc.?

73 Peter


-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Pete Lindsay
Sent: Montag, 21. Juli 2008 18:43
To: amps at contesting.com
Subject: [Amps] Help with ARRL handbook design 4CX1000A 2m PA

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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