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