Actually, you just shouldn't use that without an isolation transformer. In the old days of two wire, you could plug into the socket with the plug turned either way. usually you positioned it for the least hum, and that usually also meant the least shock when you touched it and something else. That is why older equipment usually had a ground selector switch. once your stage was set up, you went around and got all your ground switches to the best position.
Sometimes turning the plug over or flipping the switch wasn't enough. sometimes you couldn't get it right and had to flip the plug over AND flip the switch.
It was a fact of life on stage, you got shocks. Especially singing, the PA and the guitar amp were not in agreement, you hold the guitar strings, which were grounded to your amp, and touched your lips to the microphone, and WHAM, you burned your lips. I recall one night my guitarist raised his guitar up while playing, and his high E string touched the microphone, and a big spark, and his E string melted in two.
it was dangerous. On this forum, if someone starts a thread about a hot chassis amp, they usually lock the thread. SO I urge you not to use it in its natural state. With your three wire plug, the only hope you have would be MAYBE to reverse the hot and neutral wires in your plug.
But an isolation transformer is not real expensive, and if you like the amp otherwise, that is the way to go about it.
Here is a thread about your amp model on another forum:
Pepco Paul Combo - Anyone have a schematic or more info?
Are your tubes a 35W4, a 50C5, and a 12AX7? There is a link on one post with a schematic that will be close to yours, if so.