Many thanks, fellas, these are exactly the kind of tips I needed to push me in the right direction. It took me only minutes to find the culprit, though I can't say I'm thrilled: it's the flyback
In particular, it is the half of the primary between the horiz lin and the horiz output plate cap. The other half of the primary is fine. I'm afraid that means that this set has now become a big paperweight for the duration. It doesn't look like anyone ever made an aftermarket replacement; it's not in my Thorsardson or Stancor catalogs. The Andrea part number is ST-3036. I looked in the yellow pages for the number of my local Andrea distributor but somehow came up short
I have given thought to trying to repair it but I'm not sure I'm up for that adventure.
Again, many thanks for the help!
PS: When I tackle this again, I'll let you know, Banderson. I did notice a few mistakes on this Photofact and was thinking that a factory schematic would be handy. And my experience with old caps is similiar. I figure, why wait for the cap to die, why not fix it while the set is apart on the bench?
PPS: I am trying to avoid the temptation to connect the open winding in series with the second anode of another set, to try and "weld" the break!