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The earliest radio telegraph equipment were operated with heater and plate batteries or were fed by fuel operated generators, later devices operated with mains power became standard.

The classic Swiss devices can be fed by a variety of mains voltages, usually setting the voltage selector on 220 V (or 250 V , since the nominal mains voltage is 230 V today) is the correct position.

Few sets of U.S. origin are equipped with their original mains transformer wired for 110 V, these must be operated from the mains in Switzerland (or Europe) with a 110/220 V transformer. Some of the sets were later converted by radio amateurs to the Swiss mains voltages of 220 Volt - always check the voltage before connecting to the mains outlet!