I recently bought (as-is) an old Dentron Clipperton-L amp, early model
(serial #0906) without tuned inputs. The person I bought it from said it has
been sitting on a shelf for several years unused. He said when last tried,
it put out about 600-700 watts, using the three 572B tubes which are in it.
(The fourth tube had a bad filament and he removed it.)
After I received the amp, I hooked it up. Everything lights up. The panel
voltage meter reads correct volts-- about 1,800 in CW position and 2,700 in
SSB. When I flip switch to operate and activate my exciter, the relay clicks
and the red light comes on, but very little RF comes out of the amp, no
matter how I tune it. My watt meter shows about half what the exciter is
sending barefoot. The Clipperton current meter shows only about 50 mills of
current. I would expect the current to be 400-500 mills, even with just
three tubes. On SSB, the amp meter does bounce a little with modulation, but
the power is less than barefoot strength.
I checked all connections inside the amp. Nothing smelled burned. Using an
ohmmeter, the B-plus line seems O.K. from the power supply to the plate caps
of the 572B tubes. I didn't check voltage with amp running. I'm too big a
coward for that and I don't trust my voltmeter lead insulation.
The amp seems to be biased off or the signal doesn't seem to reach the
cathodes.
My questions:
1. Could the tubes just be bad or shouldn't even bad tubes show more
current?
2. Could the .01 caps feeding the input signal be bad?
3. My instruction book refers to a matching network in the parts list, but
the input in my amp goes directly through .01 caps to the filaments.
4. What is the purpose of the 9.1 volt, 50-watt zener and could it be the
problem?
5. What should I check next?
Any help will be g reatly appreciated.
73, Winston K4CWQ
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