> I am also wondering about my collection of NOS 3-1000z and 4-1000A
> Eimacs
Gas ingress or outgassing from materials inside the tube can be a
problem with any high-vacuum tube, but it seems to especially be
a problem with big glass tubes.
At the Dayton Hamvention, a friend of mine and I found several 3-
400 or 3-500Z's. They were mixed, some NOS and some used. I
asked they guy if the pulls were fresh pulls, and he said yes.
I bought the pulls and my friend bought the old new tubes. He
immediately plugged them in and blew up his amplifier (if it would
have been after the Measures reports, he would have thought it a
"parasitic").
The used tubes worked perfect.
I got the new tubes for next to nothing, cooked them up for a while
at low anode voltage, and the problems went away!
Running the filament helps on external anode tubes, because the
getting agent is heated by the filament. With glass tubes, the
gettering agent is often just sprayed on the anode. It's that flat gray
color you see on the anodes.
You have to heat that material to perhaps 1000 deg C to fully
activate it. It absorbs different gasses at different temperatures.
73, Tom W8JI
w8ji@contesting.com
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