[crispyambulance]

If we're talking homemade vacuum tubes... I wonder if it wouldn't be easier to just use metal endplates with feedthroughs for electrical (like spark-plugs) and with v-grooves for o-rings or some other gasket material. this kind of construction can handle vacuum easily, I think?

[MisterTea]

It will not hold a vacuum. Gas can diffuse through rubber and rubber itself will out-gas in very low vacuums. Metal and glass seals are the only truly air tight sealing methods. Even then, remaining gas is trapped in tubes and a getter https://en.wikipedia.org/wiki/Getter is activated at factory to trap this remaining gas on the tube wall in a thin layer of metal. That is why many tubes have a dark silver coating at the top or a band, that's the evaporated getter metal.

See also: https://en.wikipedia.org/wiki/Materials_for_use_in_vacuum

Also, don't use V grooves for O-rings. Read the Parker o-ring handbook for proper seal design: https://test.parker.com/content/dam/Parker-com/Literature/O-...

[labcomputer]

As the other replier mentioned, that won't work.

What would work is to mill a knife edge into both the end plate and the can and use off-the-shelf copper Conflat ("CF") gaskets, which are available in a large number of standard sizes.

You'd have to work out a way to hold a vacuum in the can while you're tightening the flange though

[johnwalkr]

In addition to the other comments, in general o-rings are actually very difficult to use for vacuum sealing. Unintuitively, at least until you have some experience in seal design, lower pressure differentials are much harder to seal than large ones. They depend on the pressure differential itself to form the seal, they don't work like a gasket between 2 faces. This is also why compressing in a v-groove doesn't make them perform better.

Even if you can get an o-ring to seal a vacuum, it will likely only work in the context of applying a vacuum to a system to a desired level, not as a permanent seal.

[tliltocatl]

To everyone screaming "this would not work": it would work (with right kind of fluorine rubber) as long as the lamp is attached to the pump. Thermionics (but not CRTs) don't actually need UHV, HV is good enough, so no copper conflat necessary. If you want to seal the tube off - then yes, the tube needs a proper seal and a getter. Afaik, the getter is there to counter slow outgassing of tube internals (virtual leaks) rather than any external leaks.