What do you mean?
Rare as it is, I don’t agree… as regards the device itself, 220V ac is 220V ac, regardless whether it is delivered via one wire against ground or two wires that each deliver 110V ac against ground but 180 degrees out of phase. So in theory there should be no problem (and a typical tube amp does not suffer if it is operated at 8% under voltage) but there COULD be safety problems, related to what is considered “ground”, depending on how the device is built - although without a circuit diagram or direct inspection it is impossible to tell… There COULD also be problems if a transformer designed for 50Hz is fed from a 60Hz supply, so I would be hesitant to bring non-matching equipment into the country. (EDIT: In some cases, increasing the frequency makes up for a drop in voltage, but that depends on several factors, all of which are unknown in the case under discussion.)
That’s a different set of problems, and if the stuff is valuable and supposed to last I wouldn’t bring it into this climate zone…[/quote]
For anyone who really cares about frequency issues, this is what’s happening: Lower frequency (as in 50 Hz) means more time for the magnetic field to build in the transformer before the reversing current direction causes the field to collapse (which induces voltage in the secondary coil.) Consequently, 50 Hz transformers require MORE iron in the core because if there isn’t enough, the core will saturate before the input reverses. Saturation limits the output voltage to something less than the ratio of the input and output windings.
To make a long story short: if the transformer works at 50 Hz, it will work just fine at 60 Hz. But the reverse is NOT true. (Saturation has some useful functions and can be used to build constant voltage transformers.)