Anyone use 100v or 220v gear with a transformer?

I was considering a Japanese unit (100v), and was thinking of using a Japan Voltage converter.

NO issue if you use a big enough transformer. Extremely high power 220 V devices may draw too much current for some 110v household circuits since the current will be doubled into the step up transformer.

Note that many very old devices, turntables and motors are designed to work on 50 Hz (use zero crossings or frequency for timing) and will not work properly at 60 Hz without modification. Nowadays most electronics use crystal oscillators and don't care about line frequency...although power supplies and motor windings are normally adapted to frequency too - anything with a motor may not perform in an optimal manner.

(Note that a step up transoformer does nothing to change the frequency)

Thanks, Shadorne. I am specifically interested in a tube amplifier that draws 195w maximum according to the manufacturer's spec sheet.

The step-down transformer manufacturers suggest a maximum load of no higher than 90% of the transformer's rated wattage. So, if I use a step-down transformer rated for 300w I should be fine, yes?