Zenith 25mc30 DC restoration.

[old_tv_nut]

There have been tons of discussion here about the lack of DC restoration on all tube color sets after the CT100. You are seeing it the way it was designed.
Consumer Reports complained about this yearly until solid state chassis with 100% DC restoration came along. People nowadays don't remember or never knew how these old sets performed compared to today's, and yes, it's striking.
To improve it requires modification from the original design. I don't know if you can find (here or elsewhere) posts of modifications to this chassis to improve/correct it.
You have to consider whether you want it as a true example of how it was or improved.