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Old 05-27-2013, 02:48 AM
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ppppenguin ppppenguin is offline
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Location: London, UK
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Jerome, thanks for a comprehensive reply to many of the points raised. The problems seem to split into 2 categories. Those which may be difficult but can be solved with craftsmanship and practice. And those that are a lot harder.

In the former are glassblowing skills, including the graded seals needed for Pyrex CRTs, Also the vacuum, baking and gettering techniques. These are all well known technologies, still in use for other purposes.

Things get a lot harder when replacement guns are not available. A spot welded gun can, in theory, be rebuilt using fairly simple equipment and a lot of skill. The gun of an EMI 6/6 was rebuilt this way in 1986. This is a complex hexode gun. It was rebuilt at Thorn-EMI Electron Tubes, now long gone, who specialised in photomultipliers. They certainly had the skills but not any specific jigs for that CRT. A gun assembly fused on to glass rods is more difficult. I don't know if a heater/cathode assembly can be replaced without dismantling the whole gun.

It strikes me that the hardest problem is when new heater/cathode assemblies cannot be obtained. As Jerome says, you can't remove and replace a heater from a cathode cylinder. Are h/k assemblies still available? At least they are small so storing them (in vacuo?) is not such a big problem. Making new cathodes with good emissivity and long life seems difficult. The knowhow for doing this must be almost lost.

I don't know anything about re-screening and aluminising.

Colour CRTs add a whole new set of problems.

I think others have mentioned an additional practical problem. We have a limited number of CRTs to use for learning the techniques. Each one is precious. When the original makers were making CRTs they could easily write off many CRTs as part of the development process.

It's a very brave venture. I wish all of you every succcess in keeping the craft alive.
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