[Boatanchors] 2X2 question

[J. Forster]

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).