My Hobart has a commutator for DC welding output, and slip rings for AC standby power. AC is 45 volts and goes through a transformer for 110/220. Dad got this machine new in '59.
Induction motors run fine at 70Hz, but they run 1.166 x designed speed. This is readily aparent watching an old syncronous motor clock with a sweep second hand. It is obviously fast.
Low voltage is an issue of greater concern. If the voltage is too low, induction motors may not get to sufficient speed to disconect the starting windings. In this case they WILL BURN OUT.
Universal motors [motors with brushes] are not sensitive to high or low voltage within about 20% of that specified on AC. They are not sensitive to Hz [AC frequency].
Incadecent lights are not sensitive to frequency, are dim at low voltage and bright but don't last as long on higher voltage.
Electronic balast floressant bulbs, I have no clue.
I ran the 220 volt well pump, oil burner heater, lights, TV and the computer I had at the time with that Hobart. The only thing that didn't work was a Kohler power flush toilet with an electric pump that flushes it. There is a normal one in the basment
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One of the reasons for getting the Ranger 9 was PROPER standby power, that and it is a multi process welding machine.