Crossbar Exchanges

The first Telephone eXchange Crossbar no.1 TXC1 to be installed by the Post Office was in Broughton, Lancashire in 1964. TXC sounded too much like TXE, so the designation was later changed to TXK.

Photo: Crossbar exchange, Sudbury © Martin Loach.

| EXIT | Local & Trunk | International |

TXK or Crossbar exchanges used common control and end to end selection, but were still electro-mechanical using a matrix pattern of switches and relays.

There are some shared or common control units which are only used during the setting up of the call which are then released for use on other calls in progress at the same time. The switching does not follow the same path through the exchange each time. Very simply, each end of the circuit is marked and the exchange then selects a path between between the two ends.

There were four common types of switch, plus TXK5 and 6.

Local and Trunk

TXK1 manufactured by Plessey as the ATE 5005A for use as local ND exchanges, and with modifications, also as Group Switching Centres, Sector Switching Centres and STD (Subscriber Trunk Dialling) Register Translator units. The first Telephone eXchange Crossbar no.1 TXC1 to be installed by the Post Office was in Broughton, Lancashire in 1964. TXC sounded too much like TXE, so the designation was later changed to TXK. The first production TXK1 opened in Bacup in 1968.

TXK2 the ATE 5005T, also manufactured by Plessey, for use in International Switching Centres.

TXK3 manufactured by Standard Telephone & Cables (STC) as the BXB 1112 (developed from the continental Pentaconta system) for use in Director and large Non-Director exchanges. The first production TXK3 opened in Liberton in 1971.

TXK4 the BXB 1121, also manufactured by Standard Telephone & Cables, a 4-wire register control system for use in the Transit Switching Centres and London Special Purpose Units.

International

TXK5 manufactured by L.M. Ericsson as ARM20, used in Mollison International Switching Centre, Stag Lane, London.

See also TXK5 (Thames A) in Mondial ISC.

TXK6 also by L.M. Ericsson, the AKE13 used in Thames ISC within Mondial House, London.

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