[Arran]

Ed;
  I can have a look in the U.S RCA manual if you like, I think it has a wiring diagram in it for your set that will show what is supposed to go where physically around the tone switch, or is it a potentiometer? Interesting that your RCA used one of those, I though that tone switches were more of a Philco thing, although I noticed that my new Canadian Pye radio uses one too. I never liked the tone control switch idea, it limits your choice to whatever tonal "ranges" the engineers thought best back in whatever year they were designing the set. Maybe whomever was in there before didn't like the factory choices and decided to experiment with different value caps or resistors? I always preferred the potentiometer types though I do like the arrangement several Canadian Westinghouse sets where they have a switch for selecting bass, treble, and a mid range, but also a potentiometer, combined with the Magnavox speakers they used, and the heavy wood cabinets they housed their sets in, made for a nice sounding radio.
Regards
Arran