If you plan to use an SWR amplifier that was purchased in North America in a country outside of North America, it will be necessary to change the unit's voltage so that it's compatible with the foreign country's electrical system (as with any electronic product you intend to use overseas). SWR amplifiers purchased in North America are designed to run on 120 volts; foreign current is generally 220 volts.
If you want the voltage of your amplifier changed permanently (for a relocation or long-term move), you'd need to have a a qualified repair center replace the power transformer installed in the unit's chassis to permanently convert the voltage of your amplifier.
Please note: SWR Professional Series models built before March 1999, feature multi-tap transformers and can be wired for 110v, 120v, 220v or 240v.