Building vacuum tubes

[Crow Leader]

I've started a rather ambitious project to make vacuum tubes at home. First one will be an x-ray tube.

The target pressure is 10E-5 torr, and I'm told by people with some knowledge of TV tube production that I'll want to bake out the tube at 300C if I can. The local X-ray tube companies are not really into helping with this project, and I cannot get specific numbers for pressure and bakeout times and temperatures required to evacuate a vessel say the size of a 60 watt light bulb.

Does anybody have any great stories about making tubes, or know of literature specifically about production of vacuum tubes?

[James]

There isnt really a specific bakeout temperature you should aim for - just get everything as hot as you can.  380C is the normal temperature for soda-lime glass, or 450C for borosilicate glass types.  Just keep increasing the temperature of your oven as high as you can go without the glass beginning to suck-in under the vacuum.

With a simple oil or mercury diffusion vacuum pump and no leaks you should easily be able to get a pressure of 10^-5 torr.  Its important to heat the electrodes as hot as you can, without melting them, while on the vacuum pump as well.  If you don't outgas all materials as thoroughly as is possible, then air will leak out of them a few hours after sealing the tube off the vacuum pump, and it will contaminate your internal atmosphere.

To make good tubes which last, you'll need some kind of a getter in there.  The people at SAES Getters www.saesgetters.com  are usually quite helpful and might be able to send you a few samples

Best regards,

James.

[nixie]

numerous good books on tubes are still available at the engineering libraries of most  big universities.  some will even let you look at them and check them out without being a student.

otherwise there is an o.k. book available from lindsay books it is called "instrunments of amplification" by Pete Friedrichs.
there are other good science and electronics books on the site with an emphasis on "how to" but with a good dose of "theory"

Here in madison, the Glass blower for the chemistry department is also supposed to be a good resource.  from what i understand, his job is to make test equipment like xray tubes and vacuum apparatus for the professors.   One day I'll have the time to go and find him.  I am sure there is a guy like him near you.

let us know what you find out.  I am looking to build some tubes, too, but need to work on my glass blowing skills.

best of skill and luck to you,

jon

[Audion]

Can any one explane the torr vacuum system
thanks