There would be no specific problems for guitar amplifiers beyond the usual power supply issues. A fair amount of this type of equipment is built for international use, so you might find that some of them already have a voltage selector on the rear panel for 240V use. Sometimes there is no external switch, but the transformer inside the units can have links strapped for 240V operation easily.
But failing that, they will run from a suitable 240-to-120V stepdown transformer just fine.