[Boatanchors] 2X2 question

[Mark Foltarz]

I beleive that the blue gas itself indicates mercury. 
The actual contamination is most likely just air.
The air ionizes quite easily and also ionizes the mercury vapor - just not the
way we would like...

I like the idea about the osmotic qualities of helium however. Made me stop and
think. Maybe it is atmospheric helium getting through a bad glass to metal
seal. Even though helium ionizes with a 'watermelon pink' color, the ionized
mercury vapor would surely override the more subtle helium.

You could very well goto a local university physics teaching lab and talk them
into setting up your tube in an optical spectrometer.  You could then find out
if the there are only a few lines, sharp and distinct, indicating mercury and
helium. Or if there are many lines, some sharp and others blurry, this would
indicate air.

I just went through a similar fit with 866s. Turns out the tube wasn't the
culprit at all in my situation. A feedthrough insulator was getting
intermittant when it got hot. Go figure.


de KA4JVY

Mark






--- "J. Forster" <jfor at quik.com> wrote:

> The tube is almost certainly gassy. The gas could well be helium as it goes
> right through glass. To withstand many KV, the vacuum has to be very, very
> good.
> You can tell what the gas is by using an optical spectrum analyzer or
> spectroscope on the blue light.
> 
> The good news is that 2X2s were pretty common and cheap. They were used in
> many
> WW II CRT displays (BC-929-A, ASB-5 among others)
> 
> -John
> 
> 
> Jack Antonio wrote:
> 
> > I pulled the tube and put a variable DC supply across the
> > tube, reverse biased, and the tube breaks down at about 290 volts,
> > at that voltage it has a nice blue glow inside, the higher the voltage,
> > the more intense the glow. The manual says it should withstand 12500.
> >
> > My question is, anyone have an idea of what the failure mode is?
> > (I have some replacement 2X2s coming).
> 
> 
> 
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