Principles of electronic circuits in the mechanoelectronic telephone switching system

Describes the basic circuits used in a 2000-line partially electronic exchange. In the interests of both dissipation and reliability only a relatively small number of thermionic tubes is used. For the most part the switching functions are accomplished by miniature selenium rectifiers, but some cold-cathode tubes are also used. The exchange was placed in service in May 1954 and has since provided continuous 24-hour service with a reliability equal to or greater than the highest standards normally applied.