AC In My B-

[Yamamaya42]

It kind of makes sense that there will be SOME amount of ripple on the plate side of the 10 ohm resistor, how much is the question, and how much, if any should be seen on the far side at the filters.
Before you go tracking a possible red herring, you did say you had restored another one of these sets? Perhaps it would be productive to go and see what the negative power source on that looks, and how much ripple it has comparatively, who knows, it may be the same, or you may be on to something and it is too much in the set.