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

[Dennis Monticelli]

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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