The typical USA domestic home outlet current is 15 amps at 120 VAC, so utilizing a step-up transformer can provide a maximum current of 7.4-ish without tripping the breaker. What is his amp's wattage and 50/60 Hz requirements?
As far as blowing a transformer, it's all about sellecting the correct KVA rating. If his amps draws a constant 500 watts at 240 VAC (class-A), look at transformers rated at 1500-1800 watts at 120 VAC. If a class-A/B amp, he can get by with much less.
Just some basics...