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Good Evening Gentlemen,
Answers from RACS, today, late afternoon, France:
John Marinello has a sharp eye indeed to see a glass-metal tube behind the Telefunken! - see pix below.
Metal/glass tubes are no different for us than all-glass tubes. Of course, there can be problems of separation and cracks at the glass/metal boundary, these are known problems and we have means to solve them, not always, but frequently.
Successful rebuilding of glass/metal tubes:
Success depends on mastering stresses at the glass/metal boundary, we have good experience in this domain, but no one can guarantee a 100% success rate in this operation, old glass/metal has it whims and CRT rebuilding is a mix of science & know-how, therefore some fail.
Tube aluminizing:
Correction: OK for tubes at or above 12 kV EHT, not 8kV as quoted earlier. My mistake or new directive, i don't know.
Aluminizing metal envelope tube:
Aluminum is evaporated under vacuum inside the CRT. The vaporized aluminum is therefore deposited everywhere, but in this precise case, the aluminum deposit is only important on the screen, not on the bell, which being made of metal, already has excellent conductivity. If some aluminum is not deposited on the bell and there are bare spots, the EHT wiil circulate without problems and it is not a small bare spot which will impede its passage.
What is really important, is the quality of the Al deposit on the phosphor layer. if you look at the photograph, you will see that the evaporation filament is in the direct axis pointing at the screen. Nothing will prevent the Aluminum from being deposited wether the screen is all glass or glass/metal.
For Vintagecollect:
Awaiting your data on the Red projector CRT.
Best Regards
jhalphen
Paris/France
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