[Milsurplus] [Boatanchors] Smart People: Gassy Tubes Reversable?

[J. Forster]

>  Does that perhaps imply that some of our gas troubles may be from the
> typically intermittent nature of amateur operation?

Unlikely. The diffusion rate for gas is low (else the tube would be dead);
the gettering during operation is significantly higher (else it'd not be
able to keep up).

Think of a bucket with a small hole, you're filling w/ a piutcher every so
often.

> I recall claims made to me long ago that leaving amateur gear on
> fulltime instead of shutting off after each operating session/day made
> tubes last longer, but their thinking related to preventing filament
> burnout.

Different issue. The filaments fail because of repeated stresses in the
heat/cool cycle.

> Perhaps there may be a gas capturing benefit as well?

Actually, gas diffuses through glass faster at higher temperatures, so
running a tube with filament only might actually increase the gas.

> Is this what happens: though hot tube elements outgas faster, the getter
> material is also mopping up quickly with heat enhanced chemical
> reactions, and a point may be reached where outgassing slows and the
> getter cleans it up.

I'm not convinced outgassing is a big problem, because a well made tube is
outgassed at red heat while being pumped.

This whole business can be studied with a gassy tube, by exciting it so
the gas in the tube glows and looking for atomic emission lines in the
light of the glow. I might try this if I get bored some time.

If the gas is from diffusion, I'd expect stronger He lines; if from
outgassing, I'd expect more from N2 and Ar.

FWIW,

-John

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



>
> Thanks!
>
> Wayne
>
>
>
> -----Original Message-----
> From: J. Forster <jfor at quikus.com>
> To: hwhall <hwhall at compuserve.com>
> Cc: arc5 <arc5 at ix.netcom.com>; boatanchors
> <boatanchors at mailman.qth.net>; milsurplus
> <milsurplus at mailman.qth.net>
> Sent: Tue, Dec 3, 2013 2:14 pm
> Subject: Re: [Boatanchors] Smart People:  Gassy Tubes Reversable?
>
>
>
>
> As I've written before, if you run the tube with filament and plate
> voltage, biased to 10%-20% of nominal Ip for a couple of days, many tubes
> clean up and become gas-free.
>
> -John
>
> ====================
>
>
>
> > Yes, that all rings with what I remember from physics classes. So
> tube's
> > can get gas from outside the envelope as well as from internal
> outgassing.
> > Which unfortunately still leaves us with the questions of whether
> there
> > are practical cures. The links provided by VE3BBM and W5JO seem to
> provide
> > some material for thought & experiment.
> >
> >  Wayne
> > WB4OGM
> >
> >
> >
> > -----Original Message-----
> > From: J. Forster <jfor at quikus.com>
> > To: hwhall <hwhall at compuserve.com>
> > Cc: arc5 <arc5 at ix.netcom.com>; boatanchors
> > <boatanchors at mailman.qth.net>; milsurplus
> > <milsurplus at mailman.qth.net>
> > Sent: Tue, Dec 3, 2013 1:19 pm
> > Subject: Re: [Boatanchors] Smart People:  Gassy Tubes Reversable?
> >
> >
> >
> >
> > Yes,
> >
> > Gasses diffuse through glass, even if the metal-glass seals are
> perfect.
> >
> > It depends on:
> >
> > Pressure differential
> > Glass permeability
> > Gas molecule size.
> >
> > If you have a glass Dewar and you leave it exposed to He overnight,
> it'll
> > be useless the next day. The He will diffuse through the glass and
> spoil
> > the vacuum. HeNe LASERS die for the same reason.
> >
> > BTW, gasses diffuse through metals too. Hydrogen diffuses through hot
> > Palladium very well. That's how untra-pure H2 is made.
> >
> > This same physics is use to enrich uranium, as in Iran.
> >
> > -John
> >
> > ===================
> >
> >
> >
> >
> > > >
> > > The diffusion rate through a semi-permeable membrane detends on
> the
> > > pressure difference across the membrane.
> > > >
> > >
> > > Hi, John. I think you are referring to gas diffusing through the
> tube
> > > envelope? I hadn't considered that. I was assuming gas "leaking"
> in
> > or out
> > > via wire lead seals, sort of like through nano-cracks between
> > materials.
> > >
> > > 73,
> > > Wayne
> > > WB4OGM