The AC wall plugs of vintage guitar amps are non-polarized.
That is, they can connect to wall sockets in two different ways
by simply rotating the plug 180°.
This can create a shock hazard for the guitarist
because one side of the socket carries the hot voltage and the other
side is neutral.
Our iFAQ on
Amplifier Shocks has details on why these shocks occur, what a
'death cap' is, and
what ground switches do.
This repair story shows how to install a polarized wall
plug on a Fender® Vibro Champ® guitar amp.
A polarized plug fits a polarized socket
in just one way.
A wide prong fits the neutral slot and a narrow prong
fits the hot.
Replacing a non-polarized wall plug with a properly wired, two-prong, polarized
wall plug is often all that's needed to eliminate the risk of
ground shocks in vintage guitar amps.
