The 1970s to closure

From automatic to electronic telephone exchanges.

Commercially operational satellites became available in the mid-1960s but it was clear that, as today, undersea cables and satellites would co-exist, with satellites being cheaper where random access was wanted and cables offering economy and quality on point-to-point links. In 1970 STC acquired Submarine Cables Ltd and became the sole UK manufacturer of undersea cable systems.  

The 1970s also saw the introduction of electronic telephone exchanges and STC’s TXE4 exchange became the model for UK exchanges. These exchanges handled 3,000 to 40,000 lines and gradually replaced the existing Strowger and crossbar electromechanical exchanges. In 1976, the centenary year of the telephone, the Post Office’s last manual telephone exchange closed and the first TXE4 went into public service in Sutton Coldfield. The processes of call transmission and switching were now fully automatic and based on printed circuit boards. 

In 1977 the world’s first high capacity optical cable system, including repeaters, entered service between Hitchin and Stevenage. The growth of digital technology led STC to phase out its radio operations and it closed its oldest factory, North Woolwich, in 1977.

In 1979 STC’s parent company ITT sold 15% of its shares in STC. For this purpose ITT’s UK components, business systems, research laboratories and electrical wholesaling operations were brought into the corporate entity. In 1982 ITT released a further 50% of shares and STC became a British company. STC then began to enter a period of decline with a failed attempt to enter the mainframe computer market. The company was brought out in 1991 by Northern Telecom (Nortel). In 2009 Nortel filed for bankruptcy and sold off all its assets, including STC.

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Top image: a member of staff wiring a Pentaconta crossbar frame, 1971 (NAEST 211/2/28/2)

Bottom image: Delivery of first TXE4A exchange to Leicester, February 1980 (NAEST 211/02/30/01)

Black and white photograph of woman wiring a Pentaconta crossbar frame, 1971 (NAEST 211/2/28/2)  

Black and white image of the delivery of first TXE4A exchange to Leicester, February 1980 (NAEST 211/02/30/01)