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

[hwhall at compuserve.com]

 Thanks for the clarifications. I was imagining that if a few days operating under the stated conditions helped clean them up, maybe just longer operating & idle time might convey some similar benefit, perhaps by keeping the getter material hotter longer.
>gas diffuses through glass faster at higher temperaturesI understand how a hot gas may diffuse faster through glass but I didn't foresee how hot glass made it so.
      
    >I'm not convinced outgassing is a big problemThat may very well be true. It gets a lot of blame, though, in casual conversations. Wish I knew more about the mechanics of the manufacture process. In the meantime, I'm going to hunt down that long article about getters.

An investigation of the actual gas components sounds like an interesting study & an interesting report. I wonder if anyone outside of the tube manufacturers had ever tried it? Don't think I could justify buying a spectrometer for just that one use. Though if one were cheap enough...

     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 3:02 pm
Subject: Re: [Boatanchors] Smart People:  Gassy Tubes Reversable?

>  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