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UK Phone Voice Scrambler No. 8 → ← No. 6AC/3
Telephone scrambler · 1957-1962
- this page is a stub
Introduced in November 1957 for use on CB/Auto and LB systems.
It is housed in a metal enclosure and was known as Privacy Set
rather than Frequency Changer. Rather than being GPO-exclusive,
this was the first set to become available through other commercial
parties as well.
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This version bas built around VC138 penthode valves — equivalent
to the EF91 — and offers improved performance and security.
It has a modular construction, which made it much more service
friendly in case of a fault or repair.
Security was improved by using a different frequency inversion
scheme with two stages of modulation — one at 10.0705 kHz and one
at 12.570 kHz — thereby minimising the risk of unscrambled speech
being delivered at the line in case of a malfunction of the main
oscillator. Interestingly, the feature was dropped again on the
later transistorised Privacy Set No. 8 and 9.
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Privacy Set No. 7A was suitable for the 100-110V or 200-250V AC
mains, whilst No. 7 came without a mains power supply module,
allowing it to be used with other power options, such as a 12V
DC input module.
The image above the right shows a typical Privacy Set No. 7A.
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© Crypto Museum. Created: Wednesday 26 May 2021. Last changed: Wednesday, 28 July 2021 - 05:38 CET.
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