Ground Loop

Sthomas, do you mean a ground lift switch or a hum pot?

If the hum is from the amp and not the speakers, it is probably a noisy ac transformer. If it is from the speakers and you have no hum with no interconnects attached to the amp, it is a ground loop 99 times in a hundred. One method for dealing with a ground loop is to have only one path to ground by ungrounding everything except one component, usually the line stage. There are other more complex solutions.

Mordenmail, you could use screws in the chassis connected to a spade. The best ground you would probably have is your wall plug ground. You could connect the final wire to the ground plug on a male ac plug. Neither the hot or the neutral should have any connection to them.

I suspect that you would have to lift the ac grounds of all of your ac cords or you would introduce a third path to ground and worse hum. I have never tried this solution.