Aluminized versions of the 16GP4 and 16AP4.

[Penthode]

My RCA 16AP4 had absolutely zero emission. When I collected the set, it had a brightener on the tube. The brightener simply runs the filament at a higher voltage and the extra power is to heat the cathode to bring up emission.

The earlier CRTs like the 16AP4 have fairly substantial cathodes and so I was not worried about rejuvenation. Running the cathode at 8 volts for hours made no change.

The rejuvenation process produces a controlled electrical arc between the grid and cathode to presumably strip the non-emissive and contaminated layer of oxide from the cathode. By a careful use of rejuvenation (one shot) followed by a clean, I brought the tube back up to good emission. It has been consistently good for about six months now and I no longer use or need the brighterner! Do not expect the tube to be as bright as a '60's set but at least now produces a good clean and sharply focussed image on the screen with adequate contrast. I posted some images earlier:

Note the set, an RCA 9TC275 has only 11kV to 12kV Hi-Voltage for the CRT but it is enough to provide a good watchable picture in the living room in the evening.

Remember, over doing the rejuvenation will be lethal. I have detroyed a trinitron tube with rejuvenation: one rejuv shot brought up emission and a foolish second try killed it permanently. I do not think one rejuvenation will hurt the 16AP4. And besides, what else have you to lose?

Looked at the pictures from my earlier thread.
http://videokarma.org/showthread.php?t=251172

I left the tube for six months dormant and when I fired it up again it still worked but emission was down slightly. I simply did a "clean" and it brought the emission up again. I won't be inclined to touch again.

As I mentioned earlier, I believe the tube has some gas (slight whitening of the getter) but it still works okay with no blue purple luminescence in the tube. The evacuation nipple is metal and I would guess that there is a very very slow leak...