Selenium Rectifiers--Factors in Their Application

Since their introduction in this country about 1939, selenium rectifier stacks have proved to be a useful means of converting ac power to dc power for Bell System applications. These applications vary from 2 to 2,500 volts and in power sizes from a few watts to 10 kilowatts. Properly designed, the selenium rectifier has a relatively long-life expectancy and requires a minimum amount of maintenance. For these reasons, selenium rectifier stacks are widely used in telephone plants for battery charging, relay operation, plate and filament supply for vacuum-tube amplifiers, bias supplies, telegraph and teletypewriter circuits. Up to 1952, about 245,000 rectifiers of all types have been manufactured for the Bell System. These include tungar, copper-oxide, vacuum tubes, thyratrons and selenium types. Of this total, about 25 per cent are of the selenium type. Although Bell Laboratories studies of selenium rectifier stacks date from 1939, rectifiers using such stacks did not enter the telephone plant until 1945. From 1940 to 1945, however, selenium stacks were designed 1469