I'm working on a Dumont RA-102 that has a 12JP4 picture tube. I have a chance to get a 12KP4A and I'm wondering if that's a good sub, as it seems to be from these data sheets:
http://frank.pocnet.net/sheets/127/1/12JP4.pdf
http://frank.pocnet.net/sheets/127/1/12KP4A.pdf
Nothing really wrong with my 12JP4, but this CRT is not aluminized and it doesn't use a bent gun, so it develops ion burn over time.
Unless I'm missing something, the 12KP4A is aluminized, eliminating the ion burn problem and possibly giving a little brighter picture. It also has an external aquadag coating, while the 12JP4 does not, but that's no big deal.
Regards,
Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html