The luminance deficiency was the most obvious culprit. The original white peaking coil on the contrast control above chassis had opened...I took the longest, but the most educational approach to finding it: comparing video at various points between my CT-100 and 21CT55 on a scope...I could have saved myself a half hour by following my hunch and putting a DMM on it, but the scope was more fun.
That got me a monochrome picture with all the contrast and brightness I could ask for...Turning up the color got me horizontal chroma stripes. Best yet color was actually synching periodically.
This is the only pic I got. I had it making a great picture on a different source when it would occasionally sync. Then I tried to adjust L43 (RCA part 78891) the reactance coil to make the sync permanent. It was sticky but came loose...Unfortunately, it was not the slug that came loose but the coil form and with it the wires that connected it to the terminals. leaving me with the osc. way off sync but still working. Once I realized what happened I removed the coil and tried to free the slug. Sadly the cardboard form was too brittle, and also ~1/8" of the very long slug chipped off...I managed to grab a similar form and rewind the wire, but it will not oscillate with my repair...I'm kind of up a creek presently.
Only thing I can think of is a CT-100 parts chassis....Or there is a very slim chance that coil may have been used in a 15" Dumont color monitor carcass I acquired recently. The Dumont is missing CRT/deflection hardware, flyback, and other things, but it seems to be CT-100 based. The Dumont's HV cage (what is left of it) appears to be exactly the same as that in a CT-100 as do the purity and field neutralizer coil connectors...If I'm lucky it uses the same reactance coil too...But then again I would like to make the Dumont work again someday and hacking it up for parts does not sit well with me.
After brief success, I'm back to monochrome again.