My old tube tester confirmed a short in this 6AU6 tube, which explains why a resistor fried on it's socket. I know replacement is the best solution, but old tubes are getting hard to find. I always figured shorts inside tubes occur because the parts inside are loose. Is it possible to drill into the glass, and use a pin to align the parts so they are not shorted, then shoot some epoxy inside to keep these parts solid, so they cant touch anymore?
Yes, I know they need a vacuum, so I'll have to use a vacuum cleaner to suck out the air, then epoxy the hole shut.
Have you got a source of caesium for the getter? C/H "shorts" you can often get a bit more life without "bacon & eggs" by upping the heater volts on the tester for a few seconds, to compress the oxide? back a bit. G/A shorts presumably due to thermal bending/failed spot weld unlikely. If I was going to give it a go I'd try very high magnetic field and high current through the G/A contact and arrange for the magnetic force to hopefully bend the relevant bit farther away. So shit or bust, make a G/A spot-weld or spring apart. If a structural suport failure , reorientate the valve perhaps
Aren't the getters usually calcium? Caesium has a high vapour pressure--it's used in photomultipliers, and its migration is inconveniently fast even at 20C.
Cheers
Phil Hobbs
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Dr Philip C D Hobbs
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ElectroOptical Innovations LLC
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Before I was forced to try something that drastic I'd redesign it for a transistor. Here is an ebay listing for an NOS tube for $4 including shipping. He has four of them if you want to forestall drilling into your tube for a few decades...
Iknow this is trolling, but on youtube I ran across a person that was building small tubes such as this at his house. Very interisting to watch him do it. Long time ago and I don't recall the title or where to find it.
There was one from Europe a few years ago that got a lot of travel.
But in 1964 or 65 there was an article in QST about an Argentinian who wa making tubes. He was mostly interested in making his own power tubes for transmitters, so his own design rather than copying well known tubes.
They talk about it in the areas where antique radios are discussed, there's a certain plateau one has to reach and most aren't up there yet.
What I wonder is if it was "common" in the early days of tubes. People made all kinds of things, I've read that they'd get some quartz and make their own crystals even and certainly people made their own paper capacitors in the early days, so making a tube might not be out of the norm, so long as someone had the resources. It might perhaps have been more "common" back then, since tubes were still new, but perhaps not. But it would be interesting to see if there were articles about making your own tubes back then.
Getting enough vacuum seems to be a common issue, at least once you have some success as a glass blower. I haven't seen much about whether people are making triodes or anything more complicated.
There was alot of tube bootlegging going on in the early 20s. I'm think a guy with the specialized equipment to make one tube would be strongly tempted to make a dozen or hire people and make hundreds or more.
I am not so sure. There are alot of people, especially in the US, who think you can DIY things you simply can't. It is a matter of knowing the process . At this point I wonder if tubes like a 6AU6 are bombarded like CRTs were.
At one point I thought about trying to build an EMPG but after some researc h (not posting on a forum) found out it is just about impossible without al ot of money and resources. I have come up with alot of ideas that simply we re not practical, and the ones that were were either unsaleable or already done and at the very least unpatentable.
Also, some people have no idea how to think things through. Even with an ad equate vacuum pump, just how do you get the epoxy on there ? Tubes, before final manufacturing processes have a tube through which the vacuum is pulle d ad then that is heated right near the seat of the socket, or other end an d in the atmosphere the glass tubing collapses and then you cut it off. I a m not sure when the getter is applied.
And the OP's assumption that one of the suspension components broke is a bi t off as well. The 6AU6 is a pentode right ? Does it have the suppressor gr id internally tied to the cathode ? (most do) If so the short is more likel y caused by one of those fine wires simply breaking. They are held in place by mica sheets so any misalignment could only come from traumatic mechanic al shock.
now if he has a G1 to plate short then the trauma must have been vertical a nd just made the whole thing shift down and cause the wires at the bottom g oing to the actual pins short out. Otherwise the short would read cathode t o G2, not plate. Well not necessarily.
An excellent exercise in futility for a Tuesday night. Get off the four buc ks and buy the tube and replace the resistor.
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