Tim Wescott wrote:
I have very little direct tube experience, but from what I've read it
sounds like the grid is emitting.

This is certainly consistent with what I'm thinking.

In all the old tube books this is a result of mistreating the tube --
running so much cathode current that the oxide vaporizes a bit and
condenses on the grid (although it may also happen from positive ion
bombardment -- hmm). But who knows what 50 years of sitting in a drawer
(or getting carted around) will do?

At the same time Allison says that this is what gassy tubes do, too
:-).

The explanation from Allison that there was a small crack at a pin seal
is a bit more easy to use in terms of timing of my particular problem.

I have no idea of how to actually test this theory, or what other
mechanisms would cause this problem. The best I can do is mention that
while 807's are normally $18 at Antique Radio Supply they're on sale
right now at $10

That's where mine came from, and what inspired my question "are a
certain chunk of 45-year old 807's this way?".

and 1625's are still a better buy at $5.50.

In fact I have plenty of 1625's too :-).

Tim.