this post was submitted on 27 Aug 2023
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I’m so far from an expert it’s not even funny but I’m a hobbyist for old valve (tube on the other side of the Atlantic) electronics. You need an industrial base to make semiconductors but if you can do flamework with glass and build a good enough pump that opens the door to amplifiers, radio, telecommunications, and even crude computers which in turn opens the door to a lot of creature comforts and social improvement that wouldn’t otherwise be possible.
You actually can make simple semiconductors artisanally, once again plugging Sam Zeloof. The biggest trick is getting the silicon in the first place, since you need an electric furnace to smelt it with any efficiency. Then, it's just a matter of distilling it to high purity and growing a crystal.
The pump is the biggest trick for vacuum tubes. If you have a primitive metalworking civilisation to start with, you probably have enough mercury for a Sprengel pump and/or a master craftsman who could make a mechanical pump, but if we're starting really from scratch that could be an issue. Steam to displace air + a chemical getter is another option I've been wondering about.
Also worth mentioning are electrochemical diodes, which you can make with just brine, iron and a piece of aluminum. Aluminum is tricky to make but if you can produce it it's also pretty good for wires, in case you don't have a copper mine handy.
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Electronic valves are still a thing?
I had relatives that swore on radios based on that technology could endure the detonation of bomb and still work flawlessly.
And I had a colleague in school that saved up to be able to buy a valve based guitar amplifier.
They didn't stop working somehow. The trick is that they need a very high (deadly) bias voltage to work, are mechanically delicate, have to be heated and possibly cleared of gasses leaking in, and from what I can tell have inferior characteristics for a lot of applications.
On the other hand, your relatives are right about the electrical toughness, and they have no firm upper frequency limit, so they still have industrial niches.
Yeah the guitar amp and vintage HiFi markets keep a few types (mostly power triodes and pentodes but also preamp valves and even a couple of rectifiers) in production, largely in the former Eastern Bloc. There's a few people on YouTube making their own too.