Re: Electric shocks?!
A 3-prong plug still only has one ground. If you look back at your breaker box, you'll see that the white and bare are shorted together. Kinda like green and bare in a pickup. One of the safety features of a 3-prong plug was that you couldn't put the plug in backwards. In other words, you wouldn't get "hot" on the chassis. With an older 2-prong plug, you can. Try simply reversing the plug in the socket.
But even more important, you should have a competent technician, (who has the equipment and knowledge to check AC leakage), inspect your amp. You may have an old cap, or transformer thats leaking more AC onto the chassis than should be there. More modern equipment, (built in the last 30 years or so), should have a 3 - 10 meg resistor that goes from the chassis to one side of the AC cord.
I've actually seen "junior" tech's, who's meter wasn't capable of reading ohms that high, mistake the resistor for a broken short . . . and replace it with bare wire.
Flip the plug. Check the amp. Or vice-versa.