Tesla T51 - T621E

Local-battery telephone. It was widely used on the railway and can still be seen in operation even today. The crank powered a small alternator that produced the ringing voltage, the voice circuit is powered with a battery. These telephones are still manufactured, just the cabinet is more modern. Originally, special air cells were used. These could be stored for a long time without discharging. Before usage, a plug on the cell would be punctured, the air could get inside and the cell started to make electricity.