[ARC5] [Boatanchors] More and More "Gassy" Tubes

[J. Forster]

Tubes are not perfectly sealed, and some gasses (He especially) diffuses
through glass. That's the bad news.

The good news is many can be saved. That's what the getter is for. BUT,
the tube MUST be operating for the getter to work. The trick is to power
the tube without destroying it and let the getter to do it's job.

Apply normal filament.

Apply negative grid bias to ensure cutoff through a roughly 100k resistor

Apply about 150 to 200 VDC to the plate through a current limiting
resistor to limit current to roughly 1/2 max Ip.

Slowly reduce grid bias, until Ip is about 20% of design Ip.

WAIT. At least a day.

The above an all be done on a tube tester.

Retest for gas.

-John

===================








> I'm starting to see more and more "gassy" and shorted
> tubes lately.  Even the venerable 1625.
> Not a lot- probably one out of  12-15, but that's
> way more than I saw a decade ago.
> You think these near-century-old envelope seals
> have a "shelf life?"
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