Other BT PLC sections

Events in telecommunications history


As a result of economic planning studies to determine the conditions justifying the adoption of automatic working the Engineer-in-Chief laid down the following criteria for automatic working:

  • the average subscriber's calling rate should not be less than five calls per day

  • not less than 4,000 calls per day should need to be switched automatically

  • not more than 40 per cent of the originating calls must involve manual handling.

The Electrophone exchange was closed on 30 June. The Electrophone service had been transmitted over the telephone network of the National Telephone Company, and later that of the Post Office, by the Electrophone Co. Ltd. from the 1890s. Effectively what would today be regarded as a cable company, the Company folded after the closure of the Electrophone Exchange, which followed the decline of the service in the face of competition from the increasingly accessible and varied programmes of the BBC radio service.

A new type of coin-box was introduced, the well-known Button A and Button B prepayment equipment, and for over 25 years its design remained unchanged despite various developments in the design of kiosks. It was usually installed in both automatic and central battery manual exchange areas. To make a call in automatic areas, users inserted the appropriate fee which prepared the circuit for dialling. In manual areas, callers were connected to the operator on insertion of the call fee and, in both cases, the caller then depressed Button A. This allowed the coins to be deposited into the cash box and the call to be transmitted. If a call could not be connected for some reason, or if there was no reply, Button B was depressed, the line was disconnected for five to seven seconds and all the coins were returned to the caller.

Although 6d (2p) and 1/- (5p) slots were available for other calls, the minimum fee necessary to make a local call at the time was 2d. The mechanism was originally designed to check the presence of two pennies by a weighing operation. It was set to a minimum and maximum acceptable weight for the coins as a safety margin, but as the fee was gradually increased to 3d and then 4d the safety margin became smaller and eventually unacceptable. A mechanical counter was considered too expensive as the modifications needed would have been too many and too complex. To overcome this problem a new mechanism was devised by Hall Telephone Accessories Ltd and was in effect a combination of the two basic methods: three pennies were checked by weight and the mechanism waited for the insertion of the fourth penny before allowing the call. The system required the smallest amount of additional equipment and could be easily fitted. A limitation was that it could not be easily adapted for an increase beyond 4d.

In 1959 the first versions of the new Pay-on-Answer payphones were being introduced and at the end of the 1950s began to supersede the 'Button A and B' models. This was made necessary following the introduction of Subscriber Trunk Dialling (STD) in major towns which allowed no reasonable modification to enable the 'A and B' box to be used to pay for automatically connected trunk calls. However, some 'A and Bs' remained in active use in Scotland until 1992. The primary reason for their retention lay in their remote locations. Because the boxes functioned on a single-channel radio link there was no reasonable solution for many years that would allow the use of Subscriber Private Metering (the principle on which the latest pre-payment payphones operated).

The London to Glasgow trunk telephone cable with repeaters was completed to form the backbone of the British trunk network.

Large multichange exchange areas were developed between now and 1927. Satellite exchanges were built to radiate around a main exchange to serve the centre and environs of a large provincial city, using a linked numbering scheme. Early examples were established during this time at Leeds, Edinburgh and Sheffield.

Western Electric's interests outside the USA were taken over by International Telephone Corporation (ITT). As a result Western Electric Limited in England was renamed Standard Telephones & Cables Limited.

A beam wireless telegraph service was established with Montreal, Melbourne, Cape Town and Bombay.

Back to events in telecommunications history