How to use 220V Marshall in U.S.??

[sws1]

I just picked up a used Marshall head that was originally built for use in the UK (i.e., it is not tapped for the US market).

Since I want to keep the head stock, and not mess with rewiring the connections to the transformer, what do I need to use this amp in the US?

I have seen some relatively cheap step up / step down transformers that convert from 110 to 220 and vice versa. But these things do not do frequency conversion. I'm also seen some VERY expensive variacs that allow you to choose the exact voltage.

What device to I need? Does up just step up to 220? What power requirement (# of watts) do I need on any device? Do I need to conver the frequency (60Hz to 50Hz)? etc.

I'm sure this has been done numerous times before.

Thanks