Before revision: Telephones upPolarised bell, circa 1903 Landline telephone bells were powered by 60 to 500-volt RMS at between 16 to 25 Hertz AC.
After revision: Telephones upPolarised bell, circa 1903 Landline telephone bells were powered by 60 to 500 volts RMS at between 16 to 25 Hertz AC.