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

[Dennis Monticelli]

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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