[old_tv_nut]

Thanks all for the suggestions.

The drift is quicker at first and is mostly done by 5 minutes. Just a few minutes off brings the brightness back, at least partially. I have swapped the tubes in the video section with no change in behavior.

Once the brightness has drifted to dark, off for 7 seconds is not enough to make it too bright again.

I'll check the voltage R402, R403 as suggested. The 2 uF is a good suggestion. It was replaced during the original recap, and the set hasn't had a lot of hours since, but maybe...