Vacuum tube, Measured Vacuum?

Early tubes were "soft". They left some gas in them on purpose. A "soft" tube has a higher gain, is leakier, and is less linear. Later tubes had good vacuum in them and used a "getter" to remove any remaining gasses after the tube was sealed up. The getter was in th eform of a ring and was "fired" to make the reactive material hidden inside open to the insides of the tube.

"hard" tubes have a longer life than most soft ones.

This page:

Claims a perfect vacuum is 30 inches of mercury, and is unobtainable on earth ... he further goes on to state he has used pumps able to pull 28 inches--28 inches and then the use of a "getter" in the tube should do it ...

Regards, JS

Wikipedia seems to have the answer, "historically... 10uPa to 10nPa...

Cheers

tube need?" Is there an industry standard for

"John Smith

** An article on woodturning ???????

** A woodturner said that ?

he further goes on to state he has used pumps able to pull 28

** ROTFLMAO

What a f****it you are , Smith.

....... Phil

More references

tube need?" Is there an industry standard for

Snort. Beware of the web, for it full of people that know part of something, pontificating as if they know it all. While 28 inches may be a limit for a particular class of mechanical pump (probably dry vane) pulling on wood (a porous substance) through a system that is not too well sealed (typical lathe vacuum setup), it's hardly a limit "on earth".

1 atmosphere (the pressure at the surface of the earth, on average) is 29.92 inches of mercury, or 760 mm of mercury (a unit also known as torr). Most serious vacuum measurements are in the direction of "0 is a perfect vacuum", so rather than refer to 760 torr being a perfect vacuum, we say that the room is at 760 torr, and the chamber is being pumped down to some figure approaching 0 - 1 torr, 1 millitorr (1x10-3), 1 microtorr (1x10-6) etc.

A half-decent mechanical "roughing" (wet-vane, oil bath) pump can pull a well-sealed chamber to less than 1 torr, no problem. A turbomolecular pump, oil diffusion pump, or cryo pump can pull a rather casually prepared chamber to 10-6 torr, and one that's better prepared can be pulled to 10-13 or better. If you leave a crapload of stuff in the tube envelope by stopping at 49 torr (28 inches of mercury) the getter will "get" full and leave far too much pressure in the tube. You'd want at least 10-6 (one millionth of a) torr before sealing for any hope of having the getter work properly (which will further lower the pressure in the tube). Lower is typically better, except for certain abnormal types that are using plasma in the tube.

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Along that same subject: Did that vaccum pump the guy was using appear to be homemade? After seeing that last shot of him in his workshop, it appears as though he's the sort of person who would build most of his equipment from scratch 'just for fun'.

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Paul Hovnanian     mailto:Paul@Hovnanian.com
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