Conserving our good CRT's

[dtvmcdonald]

Originally Posted by jr_tech

No, the barium surface deposited by the getter on the neck or funnel is a long term active pump, that will maintain the tube at a low pressure until it is depleted. All tubes leak, but the barium surface can insure many years of decent vacuum.

jr

Barium is not exactly a great getter. Its great for oxygen and water,
but that's about all. Its totally useless for nitrogen, hydrogen argon, helium,
and hydrocarbons. I'm not sure about carbon monoxide.

The gasses that ooze out of hot nickel, iron, molybdenum or tungsten are mostly hydrogen and carbon monoxide. I've seen this over and over
again in vacuum systems with mass specs in them. I had one that
stayed sealed for over ten years and after initial bakeout and
pumpdown that's what I saw.

For vacuum tubes with soft glass envelopes you will always see
Argon developing due to radioactive decay of potassium in the glass.
For tubes with thoriated tungsten filaments of course you will see
Helium developing.

The great getter is Titanium. It will getter anything except rare
gases and methane. That sealed system used a titanium based
ion pump. I believe that large transmitter klystrons still use such pumps.