Had a chance to put my 8877's on a commercial HiPot tester today, and I
think the tubes passed that test just fine.
Each measured ZERO current flowing, measuring between grid and plate,
with 4KV on the plate, at around 6KV started to get a couple of MICRO
amps. At 8kv it measured 9ua, and the tester which was set to end the
test at 10 microamps of current, did so around 9KV on either tube.
My curiosity is, that with the tube holding off 8kv without allowing
more than a few microamps of current, is there any difference in this
test compared to an actual burn-in with filament, bias and HV voltages
applied, except for the large amount of current that might flow if it
did flash over? I would think not, except for the tube being brought up
to operating temperature for the first time in 20 years might unleash
impurities in the vacuum? Next step I plan is to run the filaments
without HV for a day or so, just to wake them up, then throw in some HV
and Bias.
Anyway, I was pleased with the results. I also tested a recently
acquired pair of absolutely mint condition Jennings glass 10-300pf
vacuum variables, which were rated at 7500v. 1 finally hit 10 microamps
at 10kv, the other at 12kv, both set to maximum capacitance. Good to
know they are in good shape, and those things sure are nice to look at!
A HiPot tester is a very handy machine, glad my friend has one!
73 Kevin K7ZS
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