[DeLorean00]

I am working on my 1950 Mercury TV with 16KP4 picture tube. When I turn the TV off the picture collapses into a bright spot. I know other vintage TVs do this and have been told before it is the sign a worn picture tube. My concern is burning a dot into the phosphor. Is there any way to prevent this? Something I should check?

Thanks in advance,
Chris.