Todd, KA1KAQ wrote:
Geoff -
I've read a little bit about transmitting tubes that sit for long
periods releasing molecules that can form gas inside of the tube.
Someone came up with a procedure for de-gassing them with a home built
jig of some sort, to run them for a period of time getting them hot
enough for the getter to absorb the gasses and other crap that had
been released while dormant. It involves little or no voltage beyond
the heater itself.
Can't comment on your particular situation or the mechanism at work
with the low voltages, but it sure sounds like one of those tubes that
was otherwise good, but went gassy from sitting idle. Hopefully
someone with more knowledge on the subject will comment. I have a
number of old transmitting tubes in storage and worry about this very
thing.
I put that tube in the opposite socket after applying B+ (the blue glow
went away) and disconnected the plate lead on the opposite side... that
tube now draws 0 plate current. I probably killed it. In this process,
I started testing some of my spares... another draws little or no
current, one only comes up to about 150mA of plate current, when tuned
off resonance, another up to around 150mA -at- resonance, (1500vDC on
the plates) but tuning it slightly off resonance causes that particular
tube to go into a run-away current situation.
*sigh*
only 6 more to test, but they'll have to wait. Gotta pack for a 2 day
trip, leaving this afternoon.
73
