plugged 240v into 110v amplifer - is this repairable?
If it had a proper power supply (almost everything does nowadays), that would have isolated the amp itself from the mains so any damage is probably only in the power supply, most 110V switching power supplies use a voltage doubler to get something like 300-400VDC from 110AC, hooking up 240 probably generated a high enough voltage to cook the input rectifier and the switching transistors, the rest of the supply might be ok as the control electronics tends to run from a small low voltage AUX supply. This is of course assuming it used a switching supply, a good ol' fashioned mains transformer/linear regulator may have resulted in a blown pass transistor and possibly the output transistors