[Penthode]

I picked up a 9TC25 earlier this year. It had it's original tube with a brightener. Refer to the pictures on my earlier thread.

I noticed the RCA 16AP4 with a date code late in '49 had a metal instead of glass exhaust tube. I looked at the getter and the flashing was starting to curl but there was no white: I blelieve the tube is going gassy.

It had a brightener and the emission was zilch. As a last resort I tried rejuvenation and got reasonably good emission. The picture was reasonably bright and was watchable.

The emission has dropped a bit but a "clean" brings it right up again. Anyhow it remains okay for a while when a few months later another clean will again bring up the emission. (I wonder if gas is contaminating the cathode?)