[old_tv_nut]

By the way, the CTC-5 super chassis has DC coupled demods instead of DC restorers, and they bypass part of the resistor network, giving less than 100% DC restoration; so the background definitely drifts opposte the dominant color. I'm guessing they did this to reduce the effects of demodulator bias drift or differences with tube replacements, but it bothers me enough that I have considered snipping out the caps. The DC restoration of the chroma signals in the RCA X/Z demod scheme is much superior, although in those sets the luminance DC coupling is less than 100%.

The individual DC restorers on R,G,B should be best if they are stiff enough, but maybe they would have to be pulse gated to get there and what's seen is due to them not being 100% effective, something I hadn't considered until looking at these pics.

Solid state diode clamps are usually quite stiff enough, but maybe tube diode impedances are too high to work 100% without pulsed gating.

Looking at the TM21 monitor manual, I see they used a pulse-driven feedback clamp circuit.