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

Mon Apr 21 14:09:11 EDT 2014

Either. The leakage rate depends inversely on the atomic weight of the
leaking gas. He leaks relatively quickly, Ne very slowly.

-John

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

>>N2
>
> Are you all talking about nitrogen or neon? I thought the discussion was
> about neon (Ne) leaking into the tube through the glass. Did I miss a turn
> somewhere?
>
>
>
>  Wayne
> WB4OGM
>
>
>
> -----Original Message-----
> From: Dennis Monticelli <dennis.monticelli at gmail.com>
> To: J. Forster <jfor at quikus.com>
> Cc: ARC-5 Maillist <arc5 at mailman.qth.net>
> Sent: Mon, Apr 21, 2014 11:38 am
> Subject: Re: [ARC5] [Boatanchors] More and More "Gassy" Tubes
>
>
> Let me see if I understand this correctly.  I think you are saying that
> for
> N2 in particular, that molecule needs to be ionized in order to "stick" to
> the getter surface.  But since the getter surface does not have an applied
> potential (it floats on the glass envelope), there is no significant E
> field potential to attract those ions. Meanwhile there are tube electrodes
> nearby with strong attractive fields if the tube is biased for Ip.  How do
> the N2 ions find their way to the getter flashing?  I am not disputing
> what
> you are saying; you have done the experiments involving N2.  I just don't
> fully understand the role of the ionization in the N2 example.
>
> Dennis AE6C
>
>
> On Mon, Apr 21, 2014 at 10:16 AM, J. Forster <jfor at quikus.com> wrote:
>
>> 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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>>
>>
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