[Arran]

Ron, Mike;
  This is one of those things that I have been contemplating for some time now, substituting non polarized (usually poly film) in place of conventional electrolytic caps where ever possible. In radios such as my Radiola 18, Canadian Marconi XII, or Philco 96 they didn't use electrolytics at all because they either were not available (with the Radiola 18, Marconi XII), prohibitively expensive (with the 1929-1930 models), or simply not considered trustworthy. But thanks to the proliferation of devices with capacitive droppers and switch mode power supplies the number of high voltage, high value caps on the market, in more compact sizes, seems to be much more extensive then it was a few years ago, so it's not really that impractical to stuff an old Mershon (or any wet electrolytic can of suitable size) with a number of poly caps in parallel. But the number of non polarized caps of high values has also been increasing at the other end of the scale, so you can use those types as a substitute for the smaller electrolytics found in transistor radios, caps in the 1 to 10 uf range, if you have enough space, so I think I will be giving those a go too.
Regards
Arran