[Chad Hauris]

Most of the later 40's and 50's RCA, Philco, etc. AC/DC sets have an isolated circuit ground with a capacitor coupling the chassis to the power line for safety. Most of the Zenith tube type table sets run the power line right to the chassis but have it completely enclosed with insulators on the knobs and mounting screws.

I have seen schematics for some older AC/DC sets with the power line going straight to the exposed chassis, have not had to work on any. You probably could improve the safety of such sets by using a polarized cord but still I would personally use an isolation transformer, it's not worth the risk of a shock from a live chassis, and even the neutral can have a potential above earth ground and cause a shock.

I don't believe that DC is being used for residential power today! Most electronic stuff today has a switching power supply that uses a voltage doubler circuit and will not work on DC.