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wine bottle CRT/gas discharge tube

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Proud Mary

Wed Apr 18 2012, 11:07PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Ash Small wrote ...

An arc can only occur in a gas.

I'm sure you meant to add that a vacuum arc can occur under special conditions of field or thermionic emission of electrons from one electrode. For example, vacuum arcs are sometimes seen in unstable X-ray tubes where these are not fed by constant current high voltage supplies.

Ash Small

Wed Apr 18 2012, 11:36PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Proud Mary wrote ...

I'm sure you meant to add that a vacuum arc can occur under special conditions of field or thermionic emission of electrons from one electrode. For example, vacuum arcs are sometimes seen in unstable X-ray tubes where these are not fed by constant current high voltage supplies.

Thanks for clarifying that point PM.

I did contemplate this for 24 hours or so before posting, and concluded that in this case the conditions you mention wouldn't apply.

I'd be very interested in any links you may have on this subject, as I've not come across anything on this subject, but have suspected (speculated) for some time that this is possible, given the right conditions.

Proud Mary

Thu Apr 19 2012, 12:31AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Ash Small wrote ...

The Field Emission Vacuum Arc is here:

I don't think any vacuum arcs will be forming in Haxor's apparatus either.

benbradley

Thu Apr 19 2012, 02:40AM

Registered Member #312 Joined: Mon Mar 13 2006, 01:50AM
Location: Georgia, USA
Posts: 27

I recall laser project in Scientific American's "The Amateur Scientist" from the 1970's or so:

I recall one for a HE-NE laser that used two (or was it three?) cascated refrigerator pumps for the vacuum, so putting them in series can surely get a better vacuum.

2Spoons

Thu Apr 19 2012, 10:33PM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
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Posts: 615

Up to a point. The limit will be the vapor pressure of the compressor oil.

Ash Small

Fri Apr 20 2012, 12:44AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I believe that the best 'value for money' vacuum pumps (vane type backing pumps, not diffusion or turbo-molecular pumps, which need a second backing pump) are secondhand Welch units.

eg:

(This was the first I found when I typed 'Welch vacuum pump' into the USA Ebay search box.)

The best value pumps our side of the pond tend to be Edwards units.

If you want to get high vacuum pressures you'll need a diff. pump as well (or a turbo pump, but a diff. pump will probably be a lot cheaper/easier).

Proud Mary

Sat Apr 21 2012, 06:04PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Hi Haxor,

I would guess your fridge compressor can achieve pressures of a few millimetres of mercury - more than enough to make your own Geigerâ€“MÃ¼ller tubes using a mixture of helium and butane. 98.5% helium with 1.5% butane is a tried and trusted combination which can be bought inexpensively as balloon gas and lighter gas.

Ash Small

Sun Apr 22 2012, 01:25AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Proud Mary wrote ...

98.5% helium with 1.5% butane is a tried and trusted combination which can be bought inexpensively as balloon gas and lighter gas.

Balloon gas isn't pure helium, as already stated above.

I don't know what purity is required for a geiger counter though.

Proud Mary

Sun Apr 22 2012, 09:27AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Ash Small wrote ...

Proud Mary wrote ...

98.5% helium with 1.5% butane is a tried and trusted combination which can be bought inexpensively as balloon gas and lighter gas.

Balloon gas isn't pure helium, as already stated above.

I don't know what purity is required for a geiger counter though.

"It was found during the course of development that extreme purity of the filling gas and quenching vapour was unnecessary, and less rigorous pumping than that associated with most electronic tubes was also permissible, the most important factors in obtaining good tubes being cleanliness and freedom from loose particles and lint."

Source: Jenkins, RO The development of end-window Geigerâ€“MÃ¼ller counter tubes Proceedings of the IEE - Part II: Power Engineering Vol: 98, Issue: 62 pp 231 - 236 April 1951

Conundrum

Sun Apr 22 2012, 10:08AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Interesting, has anyone tried to make a multi electrode GM tube this way?

Would seem to make sense, use plastic feedthroughs and heat seal them with BiSnPb alloy.

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