Bill Ashton said:
Unless I am very much mistaken, you do not want polarity reversing...don't want the hot side shifting to the neutral side...do what I did with my Traynor YBA-1...take out the switch and put a hole plug in it...
You don't have to do that. There is a capacitor going from the fuse holder(usually) to ground. Clip that out, that's the connection to ground that you don't want(death cap). When the capacitor leaks, the chassis becomes the neutral and then you run the risk of becoming the earth ground and dead.
With a three prong plug, the chassis is connected directly to the ground plug on the cord. You can still switch polarity, but it effectively does nothing, since there is no connection to the chassis - the ac and B+ are isolated from the player. Cosmetically, it's more pleasing than a plug, IMHO. You don't need to touch the polarity switch on the Guild amps at all.