Thanks old_tv_nut! Would you believe that all appears to be working great now??
After reading your post, I pulled out my CTC11 schematic to check the demod tube... Yes, the X and Z demod are combined into one 12AZ7. The original 12AZ7 from my set tested to be very weak on my tester, so I had replaced it with an NOS Philco tube from Antique Electronic Supply. But, when you recommended replacing the demod tube, I decided to plug in the original RCA tube just to see what happens.... Powered up the set and now have RED, GREEN, BLUE all working! Beautiful picture. No sign of the red fading in and out.... watched for 1/2 hour and all was good. Will try a longer test tomorrow.
A hard lesson learned? NOS tubes can be bad out of the box? Don't assume it's good just because it's new? A tube that tests bad on the tester can still work OK? Don't forget the basics? Etc., etc., etc.
Anyway, thanks again for thinking out loud!
I'll post some new screen shots when everything is put back together and I'm sure it's working correctly.
Wes