How to make a crank style telephone?
The crank operated an electric generator, which produced ringing voltage to ring other phones on the line (in particular, the phone at the central office where an operator would connect you with the desired line by plugging a plug into a jack). But there is no longer any need for a ringing generator in a phone, because ringing voltage is supplied by the central office, and the central office knows you want attention as soon as you go off-hook. The only case you would ever need a source of ringing power is if you are doing a fully private telephone system, or setting up something like a theater prop, and for these applications you can get a gadget called a sub-cycle generator which makes the needed 20 Hz power from a 120 volt 60 Hz supply.
