[Heathkit] Low power and gassey tubes

[Shawn Duley]

You gotta love the helpful spirit of you guys. Thanks for the help.

I may now be on track to solving the low power issue.  I incorrectly
assumed that correcting all the out of spec components would clear
things up.  Especially when I was doing tube substitutions and getting
the same results.  But someone pointed out a key point that I had
suspected, but forgot to check.  It was mentioned that grid current will
drop over time if the finals are gassy.   When I was going through the
archives here and on the Tempe server serveral months ago, I remembered
a discussion on gassy tubes and the characteristic "Blue Glow".  Sure
enough, after it got dark I checked each tube and every tube tested was
gassy.  The newest set looked like a neon bulb!

Then went to the RCA handbook and found the following info:  "If a valve
has been on the shelf for a long time, it frequently shows a higher gas
current under operating conditions, but this may usually be reduced to
normal by operating the valve under normal conditions, with a low
resistance connection between grid and cathode, for a short period.
When a valve is slightly gassy, it usually shows a blue glow
(ionization) between cathode and anode.  In extreme cases this may
extend outside the ends of the electrodes, but a valve in such condition
should be regarded with suspicion and tested before being used in any
equipment, as it might do serious damage."

The handbook describes how to perform a "negative grid current test" for
gas, but doesn't really discuss the restoration procedure mentioned
above (no time frame or value given for the low resistance mentioned).

Anyone ever try to restore a NOS gassy tube??  If not, I may give it a
try after I do some serious valve theory review.  Sure would save a lot
of headaches from buying a bucket full of tubes to find a good set.

Thanks to all!
Shawn, N7PRP