Brenda Ann wrote:
"ian field" wrote in message
...

As I understand it, the electron beam is aimed slightly off centre and the
beam trajectory is corrected by an external magnetic field (the ion trap)
the ions being heavier than electrons are not deflected and collide with
the glass wall of the tube neck.

It would be interesting to know how you cantered the picture without the
ion trap.



Actually, the ion trap (there was none on the CRT when I got the set)
doesn't seem to do much with the centering, mostly it just makes the picture
darker (about 70% or so darker). The other (parts) set I have had the ion
trap, so I used the one from that set. On closer observation, I don't think
there ever has been one on this CRT, which is why I'm wondering if it is a
replacement that doesn't require one. The tube is in exceptionally good
condition for a set this old.



If the electron gun is aimed straight down the neck of the CRT,
instead of being quite noticeably at an angle, then the tube is
an aluminized screen version and does not require an ion trap.
It would probably be a 12LP4A rather than a 12LP4.
Regards, Alan