Width & Focus in DuMont RA-103

[Eric H]

I don't think it should be that far off square, the adjustments are used for centering aren't they?

I'd try adjusting it, preferably moving that one corner closer to the yoke.

I notice your Ion trap seems too far back, near the base of the tube, try flipping it over front to back and see if you can move it further forward.

After you flip it the magnet should wind up on the opposite side of the neck.

BTW, is this a Dumont 12JP4 tube? They don't use a trap at all. If it's been replaced with a 12LP4 or similar then it should have a trap but it might also explain why you can't get the focus right.

[Phil Nelson]

I assume this is a rebuild sticker, which says 12JP4. It's on the bell, halfway under the cushioned mounting strap.

It would be easy enough to take off the ion trap and see what happens.

When I first got the set, I feared it might have a bad video problem, since there was nothing on the screen but extremely faint, wandering mush. Small adjustments of the ion trap did nothing. At one point, I tried moving the trap around a lot more and a bright picture suddenly snapped in.

The trap was nowhere near working in its original position. Now the magnet is rotated roughly 180 degrees and it has been moved slightly front or back. Of course, a trap could have been nudged by accident in moving. The previous owner had the chassis in and out of the cabinet at least a couple of times.

I don't know who would put an ion trap on a CRT that doesn't use one. Maybe the same guy who hotwired the ginormous 10 mfd cap in the power supply.

Phil