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Vacuum tube, Measured Vacuum?

Discussion in 'Electronic Design' started by amdx, Jan 13, 2008.

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  1. amdx

    amdx Guest

    After watching the Triode being built, someone ask, "how much vacuum does a
    tube need?" Is there an industry standard for the vacuum in tubes?
  2. MooseFET

    MooseFET Guest

    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.
  3. John Smith

    John Smith Guest

    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 ...

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

  5. Phil Allison

    Phil Allison Guest

    "John Smith
    ** An article on woodturning ???????

    ** A woodturner said that ?

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

    What a fuckwit you are , Smith.

    ........ Phil
  6. amdx

    amdx Guest

    I just checked the first 13 of the the 442 posts phil made this new year.
    Here's some of what he said, taken completely out of context.
    The OP is a completely clueless ass.

    YOU ASS !!


    And a PITA, moronic net cop.


    Shame YOU are not - you fucking nut case.

    Only proves what a brain dead, human ostrich the ASD fucked, moronic TROLL

    Makes you just as bad as the brainless, TROLLING net cop bitch to post here
    about it.

    Especially brain dead ASD fucked criminal piles of shit like YOU and Suzy.

    How the **** would anyone here know that - you asinine shithead ??

    What you asked us was all brain dead bollocks.
    ** Shame how YOU have completely failed to *define* the problem
    ** What fucking signal ?????????????????????

    What fucking " response time " ????????????

    Only an ASD fucked moron believes others MUST be able to read their
    genetically defective, puny minds.

    YOU VILE STINKING **** !!!!!!!!

    Spoken like the asinine pile of ASD fucked human SHIT you are.

    Scum like you need a nice dose of bowel cancer.

    What a FUCKING LIAR you are.

    Typical Google scum.

    A monumental fuckwit, a smug turd, an asshole and a net cop jerk off.

    ** The bone-headed moron thinks he OWNS the newsgroup and his bizarre
    opinions are unchallenagble.

    Piss the fool off, or killfile him.
  7. Phil Allison

    Phil Allison Guest

    "a masturbating dickhead wanker"

    ** Only complete SCUMBAGS deliberately take words out of context.

    The OP is a completely clueless, fucking ass.

    ........ Phil
  8. Ecnerwal

    Ecnerwal Guest

    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.
  9. 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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