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Light Bulb Vacuum Tube

Discussion in 'LEDs and Optoelectronics' started by Twigg, Dec 29, 2011.

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  1. Twigg


    Nov 23, 2011
    Hey all,
    I've taken on a project that's probably waaay outside my abilities and experience, but what the heck. I don't really know what people might suggest or advise, so I'm just going to explain the whole project here rather than a specific question. Most of my specific questions are mechanical in nature anyways. Still, it is technically an electronics project. If you have any suggestions, just chime in.

    The project: Create a vacuum triode using only a light bulb, copper wire, some metal bits and pieces, and very basic air tools. If the grid biasing doesn't work out, I'll settle for a rectifier tube. If all else fails, I'll settle for a discharge tube.

    Progress so far: Not much. The most difficult aspect of this project is the casing. Luckily, the one thing about this project that I do have enough experience with is maintaining vacuum. The trick is that the more holes there are in the tube, the faster the air leaks in.

    With plastic tubes, I can easily get two or three screws in while keeping the leakage slow enough, the problem is mounting the filament and attaching electrodes. For one, light bulb filaments are so brittle that tweezers will cut them like scissors. For two, it's almost impossible to attach anything to the ends of the screws inside the tube. A crimping tool simply won't fit in the tube. Soldering to steel screws is always a trick, and you have to get the whole screw so hot that it melts the plastic around it, leading to more leakage and structural weakness (I've tried it). To recap: the disadvantage of plastic tubes is that attachment is virtually impossible, the advantage is relatively easy vacuum.

    With an emptied-out light bulb, you can compromise one way or another. The first option is to use a rubber stopper with and appropriate number of holes for the leads and the vacuum port. The second option is really quite bizarre. The greatest random fact ever: light-bulb contacts will just barely screw into a garden hose adapter. Who'da thunk? I only just discovered this, but I'm betting that with a bit of silicone, the seal will work just fine. the problem then is the electrical contacts. Since you obviously can't run wires in and out the bottom of the bulb anymore (you'd have to have tiny sealed conduits running out of the garden hose adapter, which is just ridiculous). Theoretically, I could forgo and use the hose adapter as the lead, with a connecter soldered onto the contact of the light bulb, but I don't like the idea of having something with high voltage connected to my hand pump, even if the hose is non-conducting.
    In light of all this, I'm wondering, is it possible to drill holes in a light-bulb without breaking it? Has anyone tried this?
    I'll just keep updating as I go.
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