I've taken a closer look and it appears that the electrician that changed out the panel, in 1985, took the ground wires from the various lines in, twisted them into one connection, with a marr connector and grounded three or four lines in, with one ground wire.

Also, my amplifier does not have a ground prong, just a post on the back which allows you to ground it, if you so wish, which I have done.

Thank you all for this,

John