[mikethedruid]

One can feel the AC from body capacitance providing a virtual ground. This is probably what you feel when the "hot" side of the house wiring (black, or sometimes red or blue, the shorter slot) is hooked to the chassis side of radio, but when the neutral, grounded side (white, the longer slot) of the house wiring is hooked to the chassis side, since it is then at earth potential, you do not feel it. If you replace the plug with a polarized one, make sure the wider prong is connected to the chassis side. Also, with SPT cord, the smooth side is used for the "hot" conductor, and the ribbed conductor is used for the neutral. cord sets with molded on plugs should already be polarized this way as it is the national electrical code standard, and the U. L. standard.