On This Day in Telephone History January 20TH 1956 - Bell Laboratories announced a new type of transistor, silicon diffused-base transistors, that could replace vacuum tubes in many telephone and TV applications. It was capable of amplifying 2500 conversations simultaneously on a telephone line, three times as many as the best previous transistor. The new transistors employed silicon wafers diffused with two different impurities to form a three layer N-P-N sandwich. The diffused N-P-N transistors could operate at frequencies up to 170 MHz which was ten times higher than earlier devices.

On This Day in Telephone History January 20TH 1956

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On This Day in Telephone History January 20TH 1956 – Bell Laboratories announced a new type of transistor, silicon diffused-base transistors, that could replace vacuum tubes in many telephone and TV applications. It was capable of amplifying 2500 conversations simultaneously on a telephone line, three times as many as the best previous transistor. The new transistors employed silicon wafers diffused with two different impurities to form a three layer N-P-N sandwich. The diffused N-P-N transistors could operate at frequencies up to 170 MHz which was ten times higher than earlier devices.