Width & Focus in DuMont RA-103

[jeyurkon]

Maybe it's just the angle of the photo, but to me it looks like a bent gun just like in the 12LP4. Maybe the rebuilder didn't have the proper gun. The Emerson 665B that I picked up recently has a 12LP4 with the single field ion trap in the same exact location that yours is. That seemed strange to me, but now yours is the second set that I've seen one placed that way.

Can you compare the gun to the photo of the one that I posted in this thread?

http://www.videokarma.org/showthread.php?t=246075

They look the same to me but your photo is at a different angle.

If it is a 12LP4 gun with a single field ion trap that may explain the angle of the focusing coil.

John

[jr_tech]

So shouldn't a 12LP4 gun (slashed field ion trap) really have a two pole magnet?

jr

[jeyurkon]

Originally Posted by jr_tech

So shouldn't a 12LP4 gun (slashed field ion trap) really have a two pole magnet?

jr

Yes, but I have two sets that came with only single field traps with their 12LP4. One adjustable single field magnet I have came with instructions saying that it could be used in place of a double field, but that it wouldn't work as well.

I'm not sure if the sets I have were that way originally or if someone replaced them.

John

[Phil Nelson]

Here's a view of the gun. It does resemble the one shown in the other thread that you referenced, but I don't know guns from Shinola. The slanted gap shown in your photo is also present in mine, just at a different angle.

I also took three photos of the set minus the ion trap. The picture is very dim, almost invisible in normal room light. In these pics, the brightness control is turned up all the way.

In the first photo, the focus coil is perpendicular to the deflection yoke, as per the manual. Notice the dark crescent in upper right.

In the second, I canted the focus coil in the same direction as seen earlier. Not quite as cockeyed as shown there, but almost. The picture is centered in the screen and I can get sorta-good (not great) focus by turning the focus control all the way clockwise.

The third is the same as Number Two, but with contrast increased for a better picture.

The picture isn't quite as blurry as seen here. My camera has a hard time finding anything to focus on in a dark room.

I assume the picture would brighten up a lot if I put the ion trap back on. All of which is interesting, but doesn't get me any closer to solving either of these problems.

There are still some things to investigate. The resistors that Eric mentioned earlier. I can check more voltages in likely places. The manual also mentions a CRT bias adjustment which I haven't checked.

Phil