[Jeffhs]

Originally Posted by ctc17

That does sound suspicious.
I have suspected that the roundie crts that have the copper pinchoff nipple leak. If you can clean the neck off and use a flashlight to look back at the pinchoff nipple and see if its glass or copper that would be interesting.

I would be interested in knowing what the symptoms of different amounts of air contamination are.
What happens if the crt looses 1-2hg vs 10hg, at what point do the filaments burn up...
Maybe miniman82 would know??

I would think any amount of air in the tube would cause the heaters to burn out very quickly. Witness how fast an incandescent light bulb burns out if it is broken while under power.