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Old 9th August 2011, 03:05 AM   #1
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Default building vacuum tubes... some questons

A kid from Germany and me are going to attempt to design and build our own vacuum tubes, even though he lives across the planet, we will work togather he will design them, and since i have most of the machinery, I will build them, but just a couple of questions...

What kind of glass do I use, and were can i get it locally? I been trying to figure what glass to use, and no web site tells what.

and how hard of a vacuum pump do we need, can i just run 2 fridge compressors in series.

don't even get me started about getters can i just buy getters from... say a sodium bulb?
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Old 9th August 2011, 08:00 AM   #2
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There is actually a place somewhere on the web that sells the glass and the metals/filament wires etc needed, Inc I think, Getters....

As to Vac. pumps, I doubt any number of series-connected fridge compressors will achieve the Vac needed for a good tube...

A few experiments with an old tube, a bell-jar and your compressors will tell you.
--But, when you try, with the old tube, keep the heaters at approx 1/2 potential when you let the vac down to air, so the cathode will be above 100 deg. C. Its Moisture from the air that kills 'em when down to air apparently....

You need summit like a Mercury or Oil diffusion pump to get a high enough vac, backed up by a GOOD vac. pump I would think.
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Old 9th August 2011, 09:39 AM   #3
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Perhaps one of the small vacumpumps for installing home heatpumps and ac will do. Not to high priced.
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Old 9th August 2011, 10:04 AM   #4
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You need to essentially put two pumps in series. A rough pump can get things down to 40-50u or so, then you kick in a diffusion pump to get to 1u or less.
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Old 9th August 2011, 12:05 PM   #5
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See the video on this page and maybe the manufacturer can help you

http://paillard.claude.free.fr/

Philippe
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Old 9th August 2011, 02:03 PM   #6
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I just love that video.

Get a swiss army knife and lets make som triodes.

Wonder how close he comes in matching from one to another.

That´s tube DIY i´ll take up knitting or something
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Old 9th August 2011, 04:42 PM   #7
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can you give me the link to were i can buy the filaments and stuff,

Ive seen the french guys video, is it possible to make a diffusion pump?
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Old 9th August 2011, 11:55 PM   #8
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Scientific American mag. had some Amateur Scientist construction articles a long while back on making a vacuum pump for tubes and lasers etc. They used two fridge rotary vane pumps in series I think. Could also check Ebay for a two stage rotary vane pump specifically for vacuum systems. Varian, Edwards, Welch, Balzers.... Then you need a diffusion pump in front of that. (although a low quality tube vacuum could be reached with just the two rotary vane pumps)

Oil diffusion pumps used to be quite cheap as surplus when they got replaced by turbomolecular pumps in industry. (avoid mercury diffusion pumps, too dangerous) Might look on Ebay for Varian or Edwards or other oil diffusion pumps. You need vacuum gages that can work to these low pressures. (not simple mechanical gauges) Thermocouple gauges are used for the pressure range between the mechanical vane pump and the diffusion/turbo pump, and ion gauges are used for the very low pressure at the input of the diffusion/turbo pump. You'll need some kind of high vacuum valve too since the diffusion pump cannot be exposed to atmospheric while in operation without ruining it and possibly causing a fire. (you cannot turn off the rotary vane pump while the diffusion pump is hot either, so another high vac valve is generally used between them also for emergency shut down) (and the ion gauge cannot be exposed to atmospheric while in operation either)

Obviously, this is not a simple hobby exercise, so consulting one of the text books on high vacuum systems is mandatory. A proper high vac. system will cost you several thousand $ even at surplus prices I expect, so you will want to know what you are doing. I have a full turbopump system in storage, but nowhere to set it up currently.
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Old 10th August 2011, 12:48 AM   #9
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You should get the classic Building Scientific Apparatus by Moore, Davis & Coplan. There's also a Lindsay reprint of an early physics text with excellent vacuum and glassblowing info. Your choice of glass will be determined by the COE of the feedthru wire (Therlo?, Invar, Kovar, etc.) You might be able to steal some feedthru wire from blown out high wattage incandescent bulbs before they become illegal. I don't know of any cheap diffusion pumps. Even a decent oil unit will cost a bit. Once you've used a turbopump, nothing else is tolerable, but they cost quite a lot. Sometimes you can find a cheap one and rebuild the bearings. It might be possible to do a cryopump, but the system needs to be really well sealed. If you're a really good glassblower, there's a complete design for a DIY diffusion pump in these peoples magazine. A rough description is online, but not enough info to build the thing. See here. You can get low cost thermocouple gage heads from Duniway Stockroom. Get the "531" model gage and build a simple circuit from The Bell Jar. IMO, you can build anything if you do enough research and are willing to improvise! Good Luck!

edit- You may want an oil trap for the roughing pump, depending on your setup. The best are molecular sieve types and the cheapest come from Thermionics because they seem to build them for everybody else. Site doesn't seem to be up right now.
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Last edited by Conrad Hoffman; 10th August 2011 at 12:54 AM.
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Old 11th August 2011, 09:00 PM   #10
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Default Diff pump

I honestly think this is about an imposable task but if you are going to do this you should start with a diff pump. I have seen some DIY diff pumps for neon work on the web. Another option would be to buy a diff pump from ebay, I have also seen a ton of them at University surplus stores. Dunaway.com has all the supplies and rebuild kits, basically it is a heater boiling oil so there are no moving parts to break. For the roughing pump I have seen a 2cfm pump at harbor frieght. Watch for air leaking into a hot dif pump all can go horribly wrong. Vacuum is not cheap or easy. Clean everything twice with IPA and then clean it again. Stay as far away from water as you can after the IPA.
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