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SA 5031
Telephone set used with scrambler phone - this page is a stub

Introduced August 1940 for use on LB (CBS 1, 2 & 3) and Magneto systems. It consists of a Tele. No. 394, fitted with a Key No. 303A switch asssembly, an 8-wire line cord, a BT20/8 connection box, and green handset 164. It is fitted with two push-buttons, labelled SECRET and NORMAL. 1

An extra push-button could be added at the centre, to provide the RECALL facility of a PABX, or for use with various extension plans. In such cases the label would be changed accordingly.

Factory assembled SA5031 units are extremely rare, as most of them were built by engineers in the field from locally available parts. Such items are generally marked Tele.No.394 on their base and chassis. Due to wartime shortages, the chassis of Tele.No.396 was sometimes used in these sets as a replacement.
Example of an SA 5031 voice terminal. Photograph kindly supplied by Andy Grant [1].

  1. Later: SCRAMBLE and NORMAL.

  1. Circular label Speech on Telephones is Not Secret (PDF)
    Crypto Museum, Reproduction, 10 June 2014.
  1. Andy Grant, Everthing that you need to know about scramblers but were afraid to ask
    Telecommunications Heritage Journal (THJ), Issue 99, Summer 2017. p. 11—14.
    Reproduced here by kind permission from the author.
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Crypto Museum. Created: Wednesday 26 May 2021. Last changed: Friday, 04 June 2021 - 08:20 CET.
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