Hi Tom,
10 to -6 or -7 sounds right to me. That would be easy enough to achieve in a
vacuum tube.
When I overheard the 70 Torr bit, the guy was reading from something, don't
remember what... it was that long ago. I thought it strange at that time but
wasn't involved in the qso and let it go. If I stopped to think about it,
the pressure would have to be well below 70 millitorr (into the "molecular
flow" region) to have a free enough path for electrons to flow from cathode
to anode. Otherwise, there would be too many molecules in the way of the
electrons, causing collisions and ionization and stuff that wouldn't allow a
tube to function.
Thanks for the info Tom!
Mike WA6FQM
>From: "Tom W8JI" <w8ji@w8ji.com>
>To: "Mike Saculla" <fqm@msn.com>,<amps@contesting.com>
>Subject: Re: [Amps] Ion Pumps
>Date: Wed, 25 Apr 2007 21:47:48 -0400
>
>>I believe a getter material is used inside vacuum tubes to get rid of
>>residual oxygen.
>
>It hopefully gets rid of all gasses, not just oxygen.
>
>
>I once overheard someone on the air say that vacuum tubes
>>have a vacuum of about 70 Torr (mm of mercury), which is not "high"
>>vacuum.
>>But I don't know how accurate that 70 Torr figure is.
>
>Not very accurate at all. As I recall 760 Torr is one atmosphere at sea
>level. 1/10th of an atmosphere is just silly. Most tubes would never work.
>
>The pressure inside a vacuum tube is normally in the 10 to the -6 or 10 to
>the -7 Torr range. Generally the vacuum pulled is as high as possible but
>some tubes demand extra care.
>
>Tubes are heated and pumped and even have high voltage applied, and most
>smaller tubes have a getter that is flashed. It's pretty near a hard
>vacuum.
>
>73 Tom
>
>
>
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