[Milsurplus] Tube storage?

[Scott Johnson]

Tubes don't generally become gassy do to in diffusion of gases, that become 
gassy because the elements within the tube, through either thermal abuse, or 
poor manufacturing, liberate gases.  The poor manufacturing some of you may 
be able to relate to with regards to some Chinese tubes.  If the gas species 
are reactive, the getter may clean them up a bit, but if not, the tube will 
be gassy.  In diffusion of Helium is most pronounced in ceramic/metal tubes, 
because the Helium has a much easier time making it through the alumina that 
it does flint glass or borosilicate glass.  At any rate, the diffusion rate 
for Helium, although impressive, doesn't affect the total pressure much in a 
common glass receiving tube, unless a glass to metal seal has been damaged, 
or there was an improper tip-off.

Scott
----- Original Message ----- 
From: "J. Forster" <jfor at quik.com>
To: "Scott Johnson" <scottjohnson1 at cox.net>
Cc: <nerd at verizon.net>; <gl4d21a at juno.com>; <kargo_cult at msn.com>; 
<milsurplus at mailman.qth.net>
Sent: Friday, March 17, 2006 11:15 AM
Subject: Re: [Milsurplus] Tube storage?


>I basically agree, see my previous post, but another thought occurred to 
>me.
>
> Has anyone tried to determine what gases are actually INSIDE gassy tubes? 
> This
> is by no means impossible. A gassy tube is really not much use, but if 
> either a
> high voltage or a HV high frequency were applied, the gas would glow. An 
> optical
> spectral analysis on that glow will tell you, from the spectral lines, the 
> type
> of gas in the tube. I actually did this some years ago on a failed Photo
> Multiplier Tube. The gas was almost all Helium.
>
> The reason this might be important is that Helium diffuses through glass 
> MUCH
> faster than the other gases, except Hydrogen and Helium is a common 
> atmospheric
> gas. Hydrogen is not for several reasons.
>
> This argues that tube storage life might be extended by storing them in a 
> pure
> Nitrogen atmosphere, which is much easier to do than a vacuum.
>
> -John
>
>
>
> Scott Johnson wrote:
>
>> As a practitioner of hi and ultra high vacuum techniques, my position is
>> that this would be impractical from an economic standpoint. A good vacuum
>> sytem capable of maintaining a 10-7 torr pressure is still very 
>> expensive,
>> and even more expensive to operate.  Glass tubes , properly manufactured,
>> and with reasonable care in storage should last 100+ years, if it were
>> neccesary, it would probably be easier to re-pump them at some later 
>> time.
>> I have not noted a "shelf life problem in any NOS tubes, with the 
>> exception
>> of ceramic-metal types(which have a much higher diffusion rate).  They
>> should be rotated into service periodically to clean them up. Ceramic 
>> metal
>> and some Eimac glass types have tantalum and titanium components , which
>> exhibit good gettering action at elevated temperatures(as in operation).
>> regards,
>> Scott
>
>
>