[Chuck Schwark]

That a/c line bypass is not needed Dave. Sounds like a previous repair person was in there. I'd carefully trace the circuit components against the schematic to be sure there are not other "mods" or possible mis-wire errors.

The radio has a power transformer and is not an AC/DC "hot-chassis" type set. Reversing the plug will do nothing or cause any safety hazzards.

The set does need, however, and external ground connection and an external antenna, so the chassis is already grounded.

I'd remove the old cap for safety, or install a Y-type safety cap in place of it. The Service Bulletin shows the Model 20 (or 21) never had any line bypass caps originally.