Voltage conversion from 220V to 110V.

Jea48...Why would heat be different for 50Hz and 60Hz AC power? Both would have the same RMS value.

I think that 50 Hz would theoretically require more capacitance in the power supply filter, because the ripple would be at a lower frequency. But I bet the difference is trivial.

Why not run them on 220 volts?

A "separate dedicated 220 volt line" is not a big deal. Your clothes dryer, stove, and maybe your air conditioner and hot water heater all run on 220.

Actually, most electronic equipment is easily changed to use 110 or 220 (sometimes as easy as a switch or plug-in jumper).

If you need to hire an electrician the US model might be best.

Jea48...The "neutral" (white) wire in our 110 volt system is connected to ground only back at the fuse/breaker box. In the electronic equipment the input power goes only to the transformer primary winding which is floating (not connected to ground).

There might be a pilot light needing replacement or a dropping resistor. A schematic would help, but I doubt that you would have much of a problem making the conversion.

Jea48...Polarity of the AC power should be of no concern because the rectifier makes it into DC anyway. Power transformers that I have worked with don't even identify the primary and secondary winding wires as to polarity, so, short of running a test on every transformer as the equipment was being built, it is not always the same from unit to unit.

I remember when there were cheap table radios (and some other stuff) that had no transformer, and the metal chassis would be hot if the plug was in one way. Furthermore, the 2-prong plugs were not polarized either. These devices relied on their plastic cases to protect the user, but sometimes an exposed screw would be hot. The occasional tingle kept us alert!

A schoolmate of mine nearly killed himself (really) with a Heathkit Geiger counter. Although the construction manual warned about the high voltages he figured "four D cells...how dangerous can it be?" Well those D cells fed a chopper and voltage step up circuitry whch produced I don't know how many thousand volts, with substantial charge stored in capacitors.