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UK
Phone
Voice
Scrambler
GPO
  
No. 6AC →
← No. 6B
  
Frequency Changer No. 6AA
Telephone scrambler · 1942-1944 - this page is a stub

Introduced in 1942 for use on CB/Auto and LB installations. Unlike its predecessors, it was built around the VC1052 signal processing valve; an octal-based penthode equivalent to the EL32.

The 6AA came in two flavours: 6AA/0 and 6AA/1, differing only in their power supplies. The 6AA/0 was suitable for the 200-250V AC mains, which was used in most parts of the UK.

The 6AA/1 was more flexible and could be powered from the 100-110V AC or 200-250V AC mains. This made the 6AA/1 suitable for use in areas that were still on 110V.

The 6AA was the first Frequency Changer to be housed in a metal enclosure. The image on the right shows a typical 6AA unit with its hinged top lid open, giving a good view of the valves (left).
  
Photograph kindly provided by Andy Grant [1]

Connections
CV1052 valve   EL32
The CV1052 is an indirectly heated pentode, introduced in 1940 for use in audio circuits. Apart from AC and DC applications, it was also used in car audio systems, either as a class 'A' amplifier or in push-pull configuration. It is equivalent to the EL32. It is also electrically (but not physically) equivalent to the EL2. It was one of the standard valves of the UK's General Post Office (GPO).

 CV1052 datasheet

Pinout as seen from the bottom of the valve

References
  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: Wednesday, 28 July 2021 - 05:36 CET.
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