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Thank you for your nice replies.
These color CRTs are unknown in Poland. Our color television started practically in the 1970s. First, we imported color cathode ray tubes from the USSR, then we launched a factory (Unitra Polkolor) under the RCA license in Piaseczno near Warsaw. I was lucky enough to be at this factory in 2007, not long before it closed.
It is not my goal to compete with the US project (Early Television Foundation CRT Rebuilding Project).
Let's talk about the technical side of this issue.
As I can see, the 21FBP22 and 21AXP22 are CRTs with a delta electron gun.
I tried to search the internet for photos of the electron guns of these CRTs, but I can't see the construction well. If it is possible to remove the cathode without destroying the Wehnelt electrode cup and the "sticks" holding the electron gun, then I think it is possible to repair such cathodes. In some Polish black and white picture tubes the cathode can be easily removed.
After removing the cathode, it will be necessary to remove (mechanically and chemically) the old layer of hydrated (after air entrainment) barium, calcium and strontium oxides from the cathode surface and apply a new layer. For the lack of any other option, not by spraying, but by careful painting. I have recipes for emission pastes. I have practically tried some of them and they are good. Unfortunately, activating such a cathode may be more difficult than activating a completely new one. This is because the old cathode nickel core may have fewer reducing impurities.
The cathode filament will also be replaced. The manufacturing technology of filaments is quite difficult (cataphoresis, hydrogen sintering, etc.). I've done some trials on this topic and the results are encouraging. When making a heater, it would be nice to know its length and diameter of the tungsten wire, so as not to do a lot of painstaking experiments. I think that making whole mechanical parts (cathode cups, Wehnelt electrode cups, etc.) would be too expensive. Parts from damaged electron guns must be used.
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