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Re: [TCML] Handmade Vacuum Tubes Video: Build A Better 811A Mousetrap?



Neal Namowicz wrote:
Hi all,
Although I've yet to attempt a VTTC (let alone make my own tube!) I've been curious about tubes, so I've been following along this thread. I'm just wondering; what the heck is a "getter"? I saw the link, so I thought, ok, now maybe I can figure it out, but that wasn't any help. Thanks in advance for the info.


A getter is some reactive metal (barium, titanium, etc.) that is deposited on the inside of something you want a high vacuum in. It's sort of like flypaper or a roach motel for stray atoms. At any reasonable vacuum, you basically have to wait for the molecule to bounce out the port to the pump, or land on the getter and get stuck there.

Typically, a barium (or other) compound is placed on a little tray, and it gets heated up, breaking down into some gas (which gets pumped away) and the metal, which evaporates onto the inside surface of the envelope (where it looks shiny and mirror like). I don't recall the exact chemistry.. maybe something like a carbonate?

You can also heat the getter up with an induction furnace scheme. If you've ever taken the base off a vacuum tube, you'll notice that some of the wires that come through don't go to a pin.. they're the wires to the getter heater.
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