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The first automatic telephone exchange in London was the 'Holborn Tandem', which opened at 10.00 a.m. on Thursday 18th August 1927. Today, the building is home of BT Group Archives. |
Automatic Exchanges
The first automatic exchange in London, the Holborn Tandem opened at 10.00 a.m. on Thursday 18th August 1927.
The first Director exchange opened on 12th November 1927.
The Speaking Clock
The service was introduced on 24th July 1936 with a pair of clocks in Holborn Tandem exchange. For this early version of the speaking clock, Jane Cain's voice was recorded photographically onto four glass discs which rotated and were scanned by a beam of light. The output from the photo-electric cells were combined to produce a complete announcement to feed into the network. By 1963, a new machine was developed to give a better quality recording. A polymer of neoprene, loaded with iron oxide and stretched onto a drum produced a resilient track on which the new 'Golden Voice' of Pat Simmons was recorded. This later equipment was installed at Trunk Control North, Kings Cross, London.
Toll B (Manual) Exchange
Switching incoming calls from the Toll Area to the Director Area.
Semi-Mechanical Tandem
Which used 7-digit keysenders over order-wire circuits also to give access from the Toll Area to the Director Area.
Temporary Toll B Non-Director (opened 1946)
This replaced Toll B (manual).
Trunk Switching Relief:
Maxwell Non-Director I/C in Holborn
In the Sixties, Toll B ND was equipped with incoming Register-Translators and became Maxwell ND I/C capable of switching traffic from adjacent charge groups into the Director Area.
BT Archives
From July 1997, Holborn became the new home of the BT Archives, a fitting place to safeguard the history of telecommunications.
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