I have an ancient Sommerkamp (German for Yaesu) FL-2500 amplifier that is
not working. If you can offer me some advice, I would greatly appreciate
it.
This amplifier covers 160 through 10m, uses five 6KD6 sweep tubes in
parallel. With 100w drive, the amp delivers about 1kW input. There is no
tuned input network and run-of-the-mill PI network output network. The B+
supply delivers a modest 1kV, just right for these sweep tubes.
Here's my problem:
- First on 20m, then later on each of the other bands, the amplifier simply
ceased to produce any output one second after applying drive. The plate
voltage is normal, and the plate current runs a steady 1A. This does not
vary no matter how much drive I apply, and no matter how I adjust the Tune
and Load capacitors. The plate current spikes up to 1A within one second of
switching to transmit, even with no drive applied. I have replaced all the
finals, and I have found a tube tester (they still exist in some obscure
places) that verified the quality of all the tubes. I have never heard any
arcing or noted any other symptom.
That the amplifier has failed one band at a time led me to suspect that the
fixed padding capacitors in the PI network might be failing. A capacitance
meter has shown these caps to be at their nominal values, at least at the
very low voltages at which that meter operates.
So, I'm flummoxed. Can any of you suggest my next step? Have any of you
had a similar problem with an FL-2500? Am I the only one left on the planet
with this amplifier?
73,
Dave VE2ZP@rac.ca
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