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No pictures, yet I don't have any time left to work on it today.
I tried the 12LP4A from the Sonora. It was made by NU-Videon or something like that. It was better, but basically behaved the same except that it really does need an ion trap.
Using the double field trap I wasn't able to adjust it properly. At the brightest position there was a shadow. It was not as bright at the position that got rid of the shadow, but the focus was good.
I then used the single field trap that was on the tube. This tube really does require a double, but the single field gave the brightest image without the shadow. The CRT is dim and blue opposite the anode connector. It looks a lot like the damage described in the article I posted about adjusting ion traps where the beam hits one of the electrodes and sputters material on to the screen. I fear that's a result of it's being used in the Sonora with a single field trap.
I think the offset raster and bad focus on the right is a geometry problem. I earlier posted that I was surprised that the cross brace still fit after moving the bridge back. Well, it is slightly off shifting the bridge to the left. I'll need to make a new brace.
It may also account for the bad focus on the right. When I mis-adjusted the ion trap I could get a good focus everywhere, dim raster though. This makes it seem like a depth of field problem. When the ion trap is mis-adjusted, only a small portion of the beam exits the gun lowering it's acceptance. That is, there is a smaller range of angles of electrons leaving the gun. This gives a larger depth of field. With a small depth of field the focal plane has to be aligned properly to be in focus everywhere. With a large depth depth of field the focal plane can be tilted with respect to the screen and still have a good focus.
This is conjecture and I'll have to see what happens when I get the bridge back into its proper position.
I'm still worried about the rebuilds not using an ion trap any more though. I wonder how long they would last this way.
John
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