----- Original Message -----
From: "Tom W8JI" <w8ji@w8ji.com>
To: "Mike Saculla" <fqm@msn.com>; <amps@contesting.com>
Sent: Wednesday, April 25, 2007 6:47 PM
Subject: Re: [Amps] Ion Pumps
>> 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.
>
I agree, Tom. If you look at curves for RF ionization breakdown
susceptibility, there is a peak at around 10 to 15 Torr. In other
words gas ionization generally gets worse before it gets better.
BTW, 2 to 13 Torr is the approximate surface pressure of Mars
which lines up nicely with the peak in gas ionization susceptibility.
This makes it especially tricky to build RF power amps, filters,
and antennas that will work there at reasonable power levels (10
to 100 watts).
73, Mike W4EF.............................
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