Metallic rectifiers in telephone power plants

THERE ARE many uses of metallic rectifiers in telephone power plants where rectifiers are required. These applications vary from 2 to 2,500 volts and in power sizes of a few watts to 10 kw. The metallic rectifiers are used primarily for charging storage batteries. However, there are many applications where the d-c power is used directly to supply relay circuits, talking battery, plate and filament for vacuum-tube amplifiers, telegraph circuits, and teletypewriters.