Paul K0DOK has built the 3cx800a7 amp. using aluminum in place of brass for the
plate line, and is not able to get the amp. to work. He has 2000 volts on the
plate, correct filament voltage, and a bias of about 5.1 volts on the cathode.
The input tunes up according to the article description, resting plate current
is about 50 ma. When tuned for a dip in plate current the grid current rises
higher than normal, and the plate current dips to a very low value. Output is
about the same as drive power. We cannot see anything wrong with the circuit
visually. The plate circuit is tuned for resonance at the low end of the band.
It looks to me like the amp is to lightly loaded? Any one with experience
with this amp, or using the 3cx800a7 on two meters have any ideas or
suggestions? Could we have a bad tube? HELP!
John, N0JA
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