Hi,

does somebody knows how long a non-aluminised CRT without ion trap can be used until an ion burn is visible on the screen? I have an English PYE LV30 with a MW22-17, this CRT has a slight ion burn:

http://upload.wikimedia.org/wikipedia/de/5/5e/IonBurnOnTVscreen.jpg

I tested the CRT, and it has more than 1.2 mA cathode current, so I assume that this CRT was not used very much.

Kind regards,
Eckhard

...

Hello Eckhard,

I found this on page 385 of Theory and Design of Television Receivers by Sid Deutsch (McGraw-Hill, 1951): "The ions cause chemical contamination of the screen phosphor after several hours of operation, to the extent that a visibly darkened center area is produced. This is known as the ion spot."

There are about four pages of discussion and diagrams.

Roger