Title: Solid state four-wire switch for key telephones

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Abstract: A compact, solid state four-wire switch for use with key telephones. The switch comprises a pair of transistors which, in the two-wire mode, electrically connect a telephone receiver with a telephone circuit balance network. In the four-wire mode a negative potential derived from the four-wire station pickup relay turns off the switch by reverse biasing the switch transistors to thereby electrically isolate the receiver from the balance network. The transistors are encapsulated within a thin, generally rectangular housing module which is adapted to be mounted interiorly of a key telephone on any of the pre-punched mounting holes therein. Electrical connection with the telephone circuitry is facilitated by three screw down terminals mounted on the module and three module leads equipped with terminal connectors.


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