1948 Bakelite Admiral Question

[Unimatic1140]

Hi Everyone, about seven years ago I recapped a 1948 Admiral Bakelite television, the model with the 10BP4 picture tube. During my recapping process I found a rebuilt 10BP4 picture tube (which had been never used since re-building) and the set ran beautifully with an amazingly bright and clear picture.

I used the set a few times a year and its always worked perfectly. I powered the set up the other day and it was working great for a few minutes, I left the room for a minute and came back and the screen was dark, but sound was fine.

I pulled the chassis and measured the high voltage at the picture tube anode connector cap, its reading between 10,000 and 11,000 volts. I also measured the voltages coming off of the cap that connects to the neck of the picture tube and they were all close to what the Sams Photofact says they should be. What is odd is when I turn the set off I get a mildly bright dot or two near the center of the screen for about 60 seconds. This makes me think that maybe its not the picture tube that has gone bad.

I'm curious how you guys think I might troubleshoot this issue? What should I be checking?

Thanks in advance everyone!