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Old 31st Aug 2019, 11:42 pm   #203
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Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: Baird T5 restoration project.

Originally Posted by FERNSEH View Post
The CRT has leakage between the anode and grid, possibly a piece of cathode material has got lodged between the electrodes.
I have been thinking about this remark.

The spacing between the anode and grid inside the tube in the CRT gun structure is very wide, quite different between say the heater & cathode or grid assembly and cathode which are closely spaced.

Not only that, inside the vacuum environment tube, unless there was a lot of loose internal aquadag, which it may not have, it is unlikely any leakage would develop between the lead out wires at the pinches, although some form of metal vapor could possibly have condensed there, but if it was getter overspill you would probably easily see it.

I think it is much more likely the leakage between the anode and grid connections is on the outside surface of the CRT, in the base, where the lead wires exit the bulb, I have seen this before.

What happens is the lead out wires corrode over time and it creates a subtle greenish film on the glass between the wires where the pinches are and between where they exit the base of the neck. This film is not soluble in contact cleaner.

If it is this problem, it needs to be sprayed with de-ionized water and the glass around the lead out wires gently stroked with a soft tool, a wooden cut down match end attached to a handle, being careful not to touch or bend the wires where they exit the bulb, as they can be very fragile, possibly corroded and break off. Then dry it with a hair dryer on low heat.

I'm not sure what the base on this tube is like or how easy it could be to remove if that was necessary to check it. Obviously before attempting it you would have to be 100% certain each wire was de-soldered and free from the pin as those lead out wires are easily broken when they are aged. And if they are going to break it will tend to happen close to the glass pinch, then its a real problem.

Last edited by Argus25; 31st Aug 2019 at 11:49 pm.
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