Here's a good article from Sylvania on the shunt regulator:
https://www.worldradiohistory.com/Ar...-News-1967.pdf
I see now how it works. It's not so much a fixed voltage regulation set to a reference as it is a constant voltage regulation by load balancing between the shunt regulator and CRT beam current.
That variable control sets the operating point. I've heard from a number of owners that these CTC5s suffer from low HV and adding an adjustment helps.
Not much to do on the IF board. Note the germanium detector diode in the lower right.
I wasn't going to remove this board, but it was just too darn dirty.
It has a delay line and funky three-legged part on the underside.
