How Come Early CRTs contained more Ions?

[tubesrule]

Originally Posted by jr_tech

Speaking of 7"crts... A 7JP4 has no ion trap, is not aluminized, was processed under primitive late 40s processing conditions, and yet, I have never seen an ion burn on one.
I may be very lucky... Or perhaps there is a better explanation for bonus points?...

jr

Electrostatic tubes do suffer from ion burn the same as magnetic tubes, but since the ions are deflected along with the electrons, it's happening evenly and extremely slowly over the entire surface, so you don't notice it. This is true not only for the 7JP4, but even pre-war tubes like the 5BP4 and 5AP4 which will never show the typical center ion burn.

The picture is of a 5" pre-war British set that was magnetically deflected. You can clearly see how large the ion burn circle is. This set ran with an anode voltage under 4KV.

Darryl