Hey Unimatic, let me just say that's a beautiful set you have there. I'm very jealous
About your problem, I would think 10kv would be sufficient, but let me ask, do you now have insufficient horizontal width? Is there any blooming or change in picture size when you adjust the brightness control?
If it turns out that the set behaves normally but just is dimmer than usual I'd go back to the ion trap. There are two places on the neck where you'll get a picture, but you'll have much better results with the location closest to the socket end.
Keep us posted
