Originally Posted by: nowonder11... What is the polarity switch and how do I know which way it should be? ...

The AC power plug is a simple two-prong thing, with no ground pin. The Polarity switch connects one side or the other to the chassis. This can be extremely dangerous! Basically, if you plug in your guitar, touch the strings and you don't die, it's probably in the right position. :eek:

In other words, don't play that amp until a qualified tech has replaced the power cord with a properly grounded three-wire cord, and disabled the Polarity switch!