Resurrecting an old thread as I am having the same issue as the OP. I have a 25MC33 Zenith Roundie that has been repaired and aligned. Last night I installed a much newer CRT which tested very good. The issue is I get retrace lines on the screen which I didn't have before. I have tried turning down all of the G2 screens, CRT bias, and brightness. I also have tried swapping the 6HE5 vertical output tube but it made no difference. C34 (.015 1kv 10%) was replaced as part of the earlier repair and R66 (150k) had previously tested good.
Thoughts on what to try next?
Here is what I get with everything turned down:
