[ARC5] [Boatanchors] More and More "Gassy" Tubes

[J. Forster]

You can store metallic Na or K under N2.  NOTHING happens. For decades.

You need the ionization to getter the N2. Do the experiment. I have.

-John

======================



> Actually, ionization is not a factor in the operating mechanism of a
> getter.  A getter is composed of a highly volatile and reactive metal.
> The
> unwanted gas molecules are agitated in their random motion by application
> of heat.  Just the heater alone is often sufficient but application of
> some
> Ip will increase the heat and also expose more of the tube elements to
> elevated temperature.  This increases agitation of the molecules which in
> turn increases the rate at which they eventually get captured by the
> getter.  If a getter depended upon ionization to do its job then there
> wouldn't be a white coating on the getter when the tube envelope cracks
> and
> lets air inside.
>
> Dennis AE6C
>
>
> On Mon, Apr 21, 2014 at 9:51 AM, J. Forster <jfor at quikus.com> wrote:
>
>> You need some Ip, IMO. If there is no electron flow, the gettering
>> process
>> does not work properly.
>>
>> It takes an electron flux to ionize the neutral gas atoms. W/o the
>> electrons, no ions.
>>
>> Neutral atoms are not attracted to anything.
>>
>> -John
>>
>> ====================
>>
>>
>>
>> > Residual gas from sitting on a shelf is very common, even with tubes
>> of
>> > relatively recent manufacture.  For example, when I replaced a set of
>> > 6146B
>> > finals that were purchased fresh in 1980 and installed in 2005, I
>> > neglected
>> > to give them a little "burn-in" before firing the rig back up for the
>> > neutralization.  My impatience was punished with a couple of
>> > inter-electrode arc's at first.  Then I just stopped and left the tube
>> > with
>> > heater and HV applied (no Ip because it was easy to run it this way)
>> for
>> a
>> > few hours.  Although the tube wasn't very hot, it was sufficient to
>> > activate the getter and clean up the residual gas.  After that little
>> > exercise the tubes performed flawlessly.
>> >
>> > Dennis AE6C
>> >
>> >
>> > On Mon, Apr 21, 2014 at 8:53 AM, Bill Cromwell <wrcromwell at gmail.com>
>> > wrote:
>> >
>> >> On 04/21/2014 09:58 AM, J. Forster wrote:
>> >>
>> >>> Tubes are not perfectly sealed, and some gasses (He especially)
>> >>> diffuses
>> >>> through glass. That's the bad news.
>> >>>
>> >>> The good news is many can be saved. That's what the getter is for.
>> BUT,
>> >>> the tube MUST be operating for the getter to work. The trick is to
>> >>> power
>> >>> the tube without destroying it and let the getter to do it's job.
>> >>>
>> >>> Apply normal filament.
>> >>>
>> >>> Apply negative grid bias to ensure cutoff through a roughly 100k
>> >>> resistor
>> >>>
>> >>> Apply about 150 to 200 VDC to the plate through a current limiting
>> >>> resistor to limit current to roughly 1/2 max Ip.
>> >>>
>> >>> Slowly reduce grid bias, until Ip is about 20% of design Ip.
>> >>>
>> >>> WAIT. At least a day.
>> >>>
>> >>> The above an all be done on a tube tester.
>> >>>
>> >>> Retest for gas.
>> >>>
>> >>> -John
>> >>>
>> >>> ===================
>> >>>
>> >>>  I have done this and had about 95 per cent success. Obviously if
>> the
>> >> glass is visibly cracked or the getter looks like chalk or cobwebs it
>> >> isn't
>> >> going to work.
>> >>
>> >> 73,
>> >>
>> >> Bill  KU8H
>> >>
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