50Hz Transformer?

[wa2ise]

A 25Hz 125V transformer will run nicely at twice the line voltage (ie, 250V) on 60Hz, IF the insulation on any high voltage secondary is good enough to take the double voltage. Also a 6.3V heater winding will now produce 12.6V.

The higher the line frequency, the smaller the core needs to be for the same amount of power to be transferred. That's the big selling point of switching power supplies. Airplanes used to use 400Hz so they could use smaller and lighter transformers. You may have seen these in surplus equipment. But a 400Hz 120V transformer will only accept 6/40 times 120V=18V@60Hz.