I'm working on a somewhat defunct 2100B for a blind friend of mine. He
drives it with an old TS520. My pal tunes both his exciter and the amp
with separate aural RF driven indicators. I've watched him do this
many time and checked it out after, and he's always very close to
right on. He operates only CW. I know squat about the 2100B, but have
reasonable experience amp experience with my home-brew 813's.
Problem: Over time the input swr to the amp appears to have gone
haywire: 4:1 or more on 40; 1.8:1 on 80; less than 1.5:1 on 20. I have
it on the bench here now and am driving it with my pro3. I can reduce
the input swr to acceptable levels with a small antenna tuner between
my exciter and his amp (or with the tuner in the pro3). The amp's
output is fed into a dummy load with a known watt meter.
Then, tuning up as per the manual for max power out, at the very best,
with 50w of drive I can get a bit more than 250W out into a dummy
load. Advancing the drive further and retuning doesn't produce a whole
lot more output -- it appears to be saturating after 50 or 60W of
drive (probably drawing lots of grid current). Plate voltage is OK.
The loading control is all the way meshed on 80 and 40. It's seems
quite normal on 20, but less power out.
I didn't want to retune the input coils if the tubes were obviously
bad. I can't get anywhere near 500ma of plate current needed for full
output -- more like half that is about it.
Is there anything else to look for before I look for new 572B's ?
Thanks for any suggestions...
Jerome - VA7VV
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