GGLL wrote:
>>>Does it still has nothing?. So it must be equal regardless inside
>>>volume.
>>>
>>
>>
>> Nothing?
>>
>> Tubes are typically pumped down to about 1E-8mmHg, which means that the
>> "vacuum" space of an amateur-sized transmitting tube will contain well
>> over a million free gas molecules.
>
> Well, I ignored that and simplified things also; then, after
>"vacuum
>process", and to "kill" those over a million molecules tube's
>manufacturer use the getter method?.
>
I don't have any specific information (so this message is also being
blind-copied to a couple of people who might know better) but my
impression is that the getter in transmitting tubes is mostly intended
to *maintain* the quality of the vacuum, not to improve it.
That wouldn't be true of small glass tubes that use a barium getter -
the silvery-looking film that has been evaporated onto the surface of
the glass. In those tubes the getter film is not created until *after*
the tube has been pumped and sealed. In that case there would be a big
improvement in the vacuum when the film is thrown onto the glass (it's a
standard cleanup technique in high-vacuum lab work). But that is all
part of the manufacturing process; afterwards, the getter would tend to
*maintain* the vacuum in its post-manufactured state.
Transmitting tubes are different because the getter is already in place
when the tubes are being pumped down, flash-heated way above the
operating temperature to remove as much gas as possible, pumped some
more and finally sealed. In that case, the getter surface would be
pretty close to a chemical equilibrium with the residual gas pressure
*before* the tube is sealed, so afterwards it would tend to *maintain*
that condition.
We're also aware from a few weeks ago that the getters used in
transmitting tubes need to be hot in order to work at optimum
effectiveness, so the vacuum can deteriorate when the tube is left cold
for long periods.
However, the basic principle is that electron tubes are quite happy to
share the space with quite large numbers of gas molecules. That is
because the electron current is usually much larger than the small
reverse ion current... but if it isn't, things can go badly wrong.
--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|