How Come Early CRTs contained more Ions?

[Adam]

I have a 7JP4 with a spot burned in the center, that is otherwise bright.

[Tubejunke]

Originally Posted by Adam

I have a 7JP4 with a spot burned in the center, that is otherwise bright.

Remember being a kid and watching the little white dot that would hang around for a few minutes after the 'family' set was turned off? This probably depends on your age. Anyhow, I think many years of that leaves a small burn in the center of the faceplate that is otherwise harmless to the tube.

I have seen many examples of ion burned tubes in old repair manuals. It seems like most were a larger circle, but of particular interest, now that I look back, is my memory of an example that was an X burned into the phosphor. I wonder how ions that supposedly can't hit the screen can do the damage I have seen, and read the heavily stressed warnings on....

I see the logic in the 'beam bender' theory, but I think there is a little more to it than that. I guess I should break out the books......

[jr_tech]

I also remember seeing pictures of CRTs with huge ugly "X" burns (rectangular tubes) and have wondered if perhaps these tubes were gassy enough to exhibit glow discharge, in which case the ion trap would do no good because the ions are not generated by the beam striking gas molecules, but are everywhere in the tube?

jr