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How do old-fashioned hand-crank telephones work? Answered

I was wondering how old fashioned hand crank phones work, in particular: Does the cranking provide power to the phone, or does it just ring the bell on the other end? I always thought that the cranking rang the bell on the other end of the line, and that the phone itself used a transformer to amplify the input from the microphone, without using power? Also, how do duplex coils keep the user from hearing their own voice through the speaker? Thanks!


The crank just generated voltage to ring the for the operator's attention. Normal conversation was powered from the central office, as is true for modern analog phones.

Not all crank magneto phones were connected to operator circuits. In rural areas, farmers built their own lines between farms. They used coded ringing to identify which farm they were calling. Two long cranks with the magneto could signal one farm and two shorts, or three shorts could signal another. The magneto only provided the alternating current to ring the bells. Direct current was needed to power the voice circuit. Each crank phone required two 1.5 volt dry cell batteries and in some cases, three were used. There were two different types of "farmer's lines" in use. One type used two wires to talk over between phones. The other type used only one wire and required a driven ground rod at each home so the return path was through earth ground. This one wire method was very noisy and made conversations difficult.

First answer is correct, of course.  The crank was attached to a magneto which generated the ring current.  I have one in the garage, but it's COLD out there (This is The Great White North, after all!!)  I'll get it later today and send a picture.  Still works, tool