Growing up in Southern California, I remember always finding old clocks with conversion stickers on them - I've been looking for a good source on the technical details to find out what they needed to do to accomplish the changeover. I'm not willing to pay 35 bucks to read the IEEE article however.
I have a ~10 year old GE microwave. After using a portable power generator which probably does not have a very accurate frequency, this winter when the grid was out, it seemed to switch itself over to 50Hz, and stayed that way after electricity from the grid was restored.
It was very confusing as the clock consistently ran too fast, and the timer ended before food got as hot as it previously had. I was surprised that something like that would be built into the microwave, and that it would be able to guess something like that. Eventually I unplugged it for a couple hours, and it went back to normal when I plugged it back in.
I recall finding a 'frequency converter' at a surplus store in LA from around the time of the war. Basically it was a motor generator set, the motor ran on 120V AC 50Hz and the generator produced 120V AC 60Hz. I asked about it and it was the first I had heard that LA had been 50Hz at one time.
I presume it was used in a lab or something, it weighed quite a bit and didn't look like something you'd have on your kitchen counter.
Having read the article, yes this was a common way - sometimes no conversion was required. Or a new motor was required, because they were using a 60hz motor to start out with (a 60hz motor running on 50hz makes more torque), and with the frequency change the motor would no longer make adequate torque.
