[Arran]

In addition to what Mike said, if you have an early AC radio, such as a Philco 77, 95, 20, or an RCA Radiola 18, these sets used large value paper capacitors for filter capacitors, between 1 and 3 uf, not electrolytic capacitors. When replacing the original filter capacitors it's best to use plastic film capacitors of a similar value, not electrolytics, small value electrolytics can't take the ripple and will inevitably fail regardless of the voltage rating. Fortunately plastic film caps are considerably smaller and more economical in larger values then their paper cap ancestors, so you might as well use them.
Regards
Arran