Early AC power systems in the US were 25Hz.

When I was in high school I was on the lighting crew.

Power for the auditorium and stage lights came into the building at, IIRC,
3+ kV and down into a 'relay room' which contained three very large
transformers to bring the voltage down to floating 120V delta (a strange
story in itself).

The nameplates on those old transformers read 25Hz!

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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