31–40 of 51 posts
Earlier quoted context omitted.
xray, photomultiplier and laser tubes are still SOTA. PM tubes in particular have a huge number of glass feed through for the intermediate plate voltages.
Musical instrument amplifiers still use them as well, at least some of them.
Hmmmm. Wonder if you could just induct through the glass with coils on each side? Seems perfect for high voltage applications?
If you want a gas discharge tube and not vacuum, you can even drop the coil on the inside: https://hackaday.io/project/194683-plasma-toroid-sky-guided-... But most hollow-state devices run on either DC or pulses, so coupled inductors wouldn't work.
Earlier quoted context omitted.
If you want a gas discharge tube and not vacuum, you can even drop the coil on the inside: https://hackaday.io/project/194683-plasma-toroid-sky-guided-... But most hollow-state devices run on either DC or pulses, so coupled inductors wouldn't work.
Wouldn't work ... without additional electronic components.
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?
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-...
Would you be able to reseal the cracked glass and regenerate the vacuum through the other end? More glass, epoxy, or similar?
Plastic generally isn't an air tight seal. The leaks may be slow, but generally we hope vacuum tubes last for years.
If I may offer an anecdote, the output stage in my guitar amplifier is powered by a GEC tube that is now 55 years old. It sounds great. When I found the tube, it had been rolling around for a couple of decades at the bottom of a wooden box.
This could simply be survivorship bias, but it does appear that back in the day, they knew how to build these things to last.
Earlier quoted context omitted.
Vacuum tubes are still made today, so I'm sure the knowledge is not lost. I'm curious about the answer as well.
I was under the impression that they were only made in eastern Europe at this point, former bloc nations. Even then, the demand must be microscopic at this point.
I’m not sure where non audio vacuum tubes are made. I’m sure there’s a variety of companies around the world making X-ray, transmitter, laser, etc. tubes.
Earlier quoted context omitted.
As mentioned in TFA, the most important factor for successfully joining a metal and a glass is to match their thermal expansion coefficients. Most pure metals have a much greater thermal expansion than any glass, which will cause cracks. In the nineteenth century, the first successful joinings of metal with glass were done using platinum, but that is obviously too expensive for normal applications. Eventually a speci…
Ordinary incandescent bulbs must have similar sealing requirements, but they probably mostly rely on using a thin conductor that doesn't contract much when it cools. Also IIRC modern incandescent bulbs do not use a high vacuum but contain a low pressure inert gas so leakage would be slower if it occurs at all.
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?
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
Earlier quoted context omitted.
Vacuum tubes are still made today, so I'm sure the knowledge is not lost. I'm curious about the answer as well.
I was under the impression that they were only made in eastern Europe at this point, former bloc nations. Even then, the demand must be microscopic at this point.
There's also a niche HiFi market, my daily driver audio amp is a 1960s Leak EL84 amp. It's a cool bit of living history and it's very non-fatiguing to listen to for long periods.