Just how bad can an Ion burn be?

[benman94]

Ion bombardment definitely does do damage to the screen. Whether you notice it is a different story. Since the ions are deflected as well, the damage that would normally be a big nasty dot in the center of the screen is spread out over the whole screen. To get adequate brightness out of a damaged phosphor back you crank up the controls. Of course the cathode is wearing simultaneously as well, so eventually, the pairing of a damaged phosphor and a weak cathode gives the tell-tale shimmering, and eventually negative, picture. If you could isolate the effect of the ion bombardment though, let's say with some super long lasting cathode material, you would see detriment to the screen.

You're also correct in saying that on a 7JP4 you would expect to see the ion damage in the region of the previously scanned raster.

On the 10BP4 or 12LP4, it was assuredly damage from the electrons themselves; the ions were shot off into the wall of the neck. Remember that an electron in the region of ~2 keV in a lowly 7 inch Transvision to ~75 keV in some projection sets can and will do incremental damage to the phosphor. Ever seen a burned 5TP4? That was done by a beam of electrons at 25-27 keV over some extended period of time.

[Kevin Kuehn]

You don't suppose that the anode voltage in conjunction with the shape of the CRT envelope has some influence on the ion defection pattern? There's got to be some electrostatic effect involved between the anode and ions.

[jr_tech]

Originally Posted by Kevin Kuehn

You don't suppose that the anode voltage in conjunction with the shape of the CRT envelope has some influence on the ion defection pattern? There's got to be some electrostatic effect involved between the anode and ions.

Have we considered ion production in the space between the deflection yoke and the screen? For sure, there were a number of un-aluminized rectangular crts produced in the 50s that had an ion trap, but the screen possibly could have been bombarded by ions produced past the electron gun.

jr

[benman94]

Originally Posted by jr_tech

Have we considered ion production in the space between the deflection yoke and the screen?

jr

What's going to produce the ions? Are we assuming that the electron beam interacts with residual gas, and ionizes it post-deflection? That's an interesting angle, but I don't see how the X pattern results...

[jr_tech]

Originally Posted by benman94

What's going to produce the ions? Are we assuming that the electron beam interacts with residual gas, and ionozes it post-deflection? That's an interesting angle, but I don't see how the X pattern results...

Yes, but I don't have a clue as to how the x shape might be produced.

jr

Perhaps a bit of argon, as well?

.

[Kevin Kuehn]

I was thinking the geometry of the envelope could have some influence on the distributed static field. A round envelope would seem to have the most even distribution.