[Arran]

These sets, as well as all other Philco AC/DC or transformerless power supply designs, have the common negative isolated from the chassis, they are NOT hot chassis sets. They chained all of the B- points together with a bus wire and then coupled the chassis to the B- with a capacitor-choke assembly and a resistor. It does not make it 100% safe but still much better then having the power line soldered directly to the chassis.
I've seen the polarized plug idea circulating for a few years and believe that it gives a false sense of security. For one thing how do you know that the outlet is connected correctly? For another even with the polarized plug that will only work if the set if on, if it's off you will find that it still gives a tingle if you rub your knuckle on the chassis.
The shock hazard was not unknown even when these were new, there were warnings with all of the literature about connecting a ground, and steps were taken to prevent someone from touching the chassis itself such as having a back and plastic knobs. In fact some Philco Transitone sets originally had rubber covers to insulate the chassis screws.
There are two ways to make an AC/DC sets 100% safe, treat it with respect, or operate it through a GFI outlet or an isolation transformer.
Regards
Arran