Making glass-to-metal seals for homemade vacuum tubes

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Making glass-to-metal seals for homemade vacuum tubes

zdw

Comments (41)

tliltocatl
One thing about gallium/galinstan - it would actually make a descent high vacuum seal as it has lowest vapor pressure of all elements - so it doesn't evaporate. The problem is that it sticks to just about everything that isn't PE/PTFE. Galinstan thermometers use some proprietary coating to make glass repel it.I was once entertaining the idea of using gallium for an electrostatically or MHD boosted Sprengel pump, but figured out sticking would make it infeasible. And now it's unobitanium too.
alister
What was the large-scale commercial procedure for making electrodes that pass through the glass without letting air in? I assume that electronics manufacturers must have been making millions of such vacuum tubes in the past. Is the knowledge lost (or not practical for hobby use)?
SyzygyRhythm
The article mentions that thin-walled copper tube can be used, but then says a precision lathe is required. But you can easily buy off-the-shelf copper tube with 1.6 or 2.0 mm diameter and 0.5 mm wall thickness. Is that not thin enough? If not, could one chemically thin the walls (acid, electrolysis) until it is enough?
tyingq
The research here is clearly interesting, but if you just need to get something like this working, premade neon tube electrodes are plentiful and inexpensive.
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?
egl2020
Love this kind of fearless DIY. Keep at it.
kazinator
> For the seal, this is a good thing: less metal means less expansionBut power tubes need to pass some decent amounts of plate current through some of the pins. Even small signal tubes have considerable current going through the heater filaments; you don't want hookup wires for that which are like metallic spider silk.
projektfu
I was wondering about the feasibilty of this, but I thought that useful tubes needed a harder vacuum than that. Is this really "good enough" for a triode?I figured the wire-holding/element-holding aspect of a standard tube was in the base, and the glass-to-base seal is the important part. You can have a less-hot metal holding the filament and penetrating through the base. But I haven't looked carefully. These are my off-the-top-of-my-head thoughts about it.
mmmlinux
I'm surprised there was no mention of Fernico or Dumet metal. they were designed for this application.[0] https://en.wikipedia.org/wiki/Fernico
smlacy
Hmmmm. Wonder if you could just induct through the glass with coils on each side? Seems perfect for high voltage applications?
LgWoodenBadger
Would you be able to reseal the cracked glass and regenerate the vacuum through the other end?More glass, epoxy, or similar?
bsder
Erm, don't the guys making homemade Nixie tubes have this figured out?https://www.youtube.com/watch?v=wxL4ElboiuA