[Arran]

There were 25 cycle power grids in both Canada and the U.S, though they were more common in Canada. From what I was reading there were also some 40 cycle power grids as well. There is a summary on Wikipedia about what power line frequencies were used and where. I've never heard a or read a comprehensive explanation as to why 25 cycle was used, one theory is that it was for industrial uses like rolling mills for steel. My theory is that a lot of early power companies in Canada used to buy equipment from Britain, where they used 230 volts at 50 cycles per second, so I think they may have modified the equipment to run at half voltage and half speed just to use it here.
In any event if you look at the specs of a 25 cycle transformer not only is there more iron in the core, to prevent the core from being saturated, there is also a higher DC resistance to the primary, so they are really not bothered by a higher line voltage. Most radio manufacturers in Canada offered sets with 60 cycle transformers or 25/60 cycle transformers, Rogers-Majestic/Standard Radio used 25 cps transformers in all their sets regardless of where they were sold.
Regards
Arran
Regards
Arran