TXE4
The TXE4 was a cost reduced development of the TXE3 system and catered for up to 40,000 subscribers with over 5,000 erlangs of bothway traffic and was normally staffed by several Technical Officers (TO). This was developed purely by STC to a specification from the GPO. It was built at the STC Southgate factory in north London and used reed relays as the switching medium which proved reliable in service. Later a small amount of exchanges were also manufactured by Plessy and GEC. It had a programmable common control called the Main Control Unit (MCU) and each exchange had at least three MCUs for security and a maximum of twenty, but in theory could operate with just one. It had a unit called the Supervisory Processing Unit (SPU), which took control of the calls from information supplied to it by the MCU.
The man responsible for marketing strategy of STC at the time, Ken Frost said “We took a chance on going into TXE4. In the first place without any firm commitment from the Post Office. And then we got into the great modernisation programme, in which we argued for modernisation with TXE4 while Plessey and GEC made their case for crossbar with some electronic control on it. The Post Office decision was for TXE4”.
To prove the enhancements of TXE4 over the TXE3 a test bed trial installation was installed in Tudor exchange in North London in 1969. After a successful two-year trial a contract was placed with STC for the provision of £15million of TXE4 equipment in June 1971.
The first actual production TXE4 was installed in 1973 at Rectory, a Birmingham area exchange at Sutton Coldfield, and brought into service on 28 February 1976. TXE4 is sometimes known as TXE4RD where the RD stood for Rectory Design. Rectory opened with 4300 subscribers and had a maximum capacity of 8000. In 1983 there were 350 TXE4s in service serving 4 million customers. The last TXE4s were taken out of service (at Selby, Yorkshire and Leigh-on-Sea, Essex) on 11 March 1998.
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