Just how bad can an Ion burn be?

[Eric H]

I've heard the theory about Ions ruining 7JP4's before, maybe theoretically possible but I have my doubts that it happens in practice.

I've had plenty of tired 7JP4's, but they pretty much were all bad the same way, very dim and going negative at higher brightness.

Maybe I've just never come across one with a burned screen that still had good emissions since high hours and burned screen would go hand in hand.

Still I would expect an Ion burned tube to be burned only where the image was, in other words if you increased the scanning height or width it should be okay at the edges.

I have seen one 10BP4 (or maybe it was a 12LP4) where you could tell where it had been scanned most of it's life, if you rotated the yoke you could tell the difference in the color of the phosphor. I'm guessing that was simply worn phosphors and not Ion burn.