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I had a Waring Blendor [sic], cat. no. 700A, with the widest range I've ever seen: "115 Volts, 6 Amps, 25 to 60 cycle A. C. - D. C." I haven't been able to pin down an exact date on this model, but it seems to date from the 1940s or so, when the U. S. power grid still hadn't completely settled on a standard. I've read that portions of Boston still had 110 volts DC in residential areas up through the 1960s, though I've been unable to find much detail about this.

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That's because it's quite common for simple appliances to use a universal motor.

https://en.wikipedia.org/wiki/Universal_motor

It basically doesn't make a difference what polarity you feed it, if it's positive going into the rotor then it's positive going into the stator as well. When the rotor changes polarity, so does the stator.

The motor on my mum's Singer Featherweight model 3-120 sewing machine runs on 110-120 volts 25-75 cycles AC and DC. It was made around 1950.

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