Other BT PLC sections

Events in telecommunications history


All Figure Numbering (AFN) was introduced - starting in the Director Areas (London, Birmingham, Edinburgh, Glasgow, Liverpool and Manchester). AFN had become essential with the development of direct international dialling as the mixed letter and number combinations were insufficient to meet the needs of expanding service.

Telephone No. 712 - later No 722 - (the 'Trimphone') was made generally available.

This innovative design by STC, half the weight of the more traditional 700-type telephone, originated in 1961 when the Post Office decided it needed a luxury telephone to add to its range. Towards the end of 1963 the Post Office settled on the design by STC, and in 1964 placed a contract for 10,000 units. The first example of the Trimphone was presented in May 1965 by the Postmaster-General, Anthony Wedgwood Benn, to a newly wed couple in Hampstead in a ceremony marking the installation of the ten millionth telephone to be installed in Britain. The new design was trialled in the London North West Telephone Area in the same year, before becoming available throughout the country in 1966 in three two tone colour combinations. By 1980 there were 1.6 million in operation out of a total telephone population at that time of 27 million.

The Trimphone was an entirely new and lightweight design, which among its novel features incorporated the receiver and microphone in the earpiece as a composite unit. The user spoke into the handset in the normal manner, but the sound was carried up inside the handset to the microphone. Because the handset was hollow, as opposed to the solid mouldings of earlier phones, this was the first telephone with the feature of which most modern phone users are now wary. If the user attempted to place a hand over the microphone in order to make a confidential aside, the sound was still transmitted inside the handset with embarrassing results.

Another feature was a tone call device in place of the conventional bell, which had a volume control to suit the preference of the subscriber. A transistorised oscillator connected to a miniature loudspeaker produced the warbling tone.

However, possibly the most striking out of many new features was the luminescent dial, which glowed green in the dark. This effect came from a small glass tube of tritium gas, which gave off beta radiation and made the dial fluoresce. Although the radioactivity was equivalent only to that given off by a wristwatch, with people less likely to have as close or continuous contact as a timepiece, it was later felt wise to withdraw this facility as public concern over radioactivity grew. By 1981, towards the end of the general availability of the Trimphone, a keypad version was marketed. BT later invested in a widely publicised initiative to safely recover and dispose of Trimphones from customers' premises.

The first fully operational production electronic telephone exchange in Europe (the first small-to-medium sized one in the world) was opened at Ambergate, Derbyshire. This was a TXE2 reed relay exchange.

The TXE2 was a result of research into space division electronic exchanges  and its introduction was part of the major programme of investment into the network by the Post Office using modern switching equipment which began around this time. Initially, the TXE2 was used for exchanges with a capacity of up to around 2,000 lines. The Plessey 5005 (TXK1) crossbar exchange, also produced under agreement by GEC, was used for larger installations in non-director areas and group switching centre exchanges. The BXB (TXK3) crossbar exchange, a derivative of the ITT Pentaconta crossbar system developed in France, was made by STC for larger installations in director area and trunk-transit exchanges.

The TXE4 electronic exchange, a development complementing the TXE2, was introduced from 1976 to take over from crossbar the provision of large exchanges.

During the 1980s and 1990s the TXE and TXK families of electronic and electromechanical exchanges were gradually replaced with System X and System Y digital exchanges in a £20 billion investment programme. The last TXE2 exchanges (Ballycastle, Northern Ireland, Llandovery, Wales and Ramsbury, England) were closed on 23 June 1995. The last TXK crossbar exchange, at Droitwich, was withdrawn in 1994.

The UK network became totally digital on 11 March 1998 with the closure of the last electronic TXE4 exchanges at Leigh-on-Sea and Selby and their conversion to System Y (AXE 10) and System X respectively.

The first Dial-a-Disc service was opened in Leeds.

Back to events in telecommunications history