English: Hand-cranked dynamo electric generator of type used in ringer telephones, by W. Gurlt. It consists of two horseshoe-shaped permanent magnets that create a magnetic field between their poles at bottom. A wire-wound armature rotates in this magnetic field. Turning the crank spins the armature at high speed, attached to the small pinion at bottom turned by the large gear wheel. The changing flux induced an alternating current in the wire winding. The winding is attached to a commutator, a rotating contact on the armature shaft, that reverses the connection every half-turn, rectifying the alternating current to a pulsing direct current which is supplied to an external circuit via contacts on the back of the machine.