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Old 18th May 2019, 7:52 pm   #17
AC/HL
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Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,637
Default Re: GPO/BT Call Progress Tones?

As I remember, the tones were generated by the ringing generator. The cam operated spring sets for the cadence were fascinating to watch, in an anoraky sort of way. All electronic now, enabling voices as well as tones.
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