[Milsurplus] Tube storage?

[J. Forster]

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