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Old 18th May 2019, 6:58 pm   #15
Join Date: May 2010
Location: Grantham, Lincolnshire, UK.
Posts: 717
Default Re: GPO/BT Call Progress Tones?

It is a long time ago, but I can't remember any parts of the call route in an exchange with tones on them other than the first selector and final selector. Used ot have a special tag block with the S and Z pulses, and the tones, all done in 0.9mm, 21swg, wire.

I think even the busy, NU, etc tones were all passed back to the first selector to stop equipment being held when not carrying a call.

You needed a special relay to do the tones, mu-metal sleeving on the core or something.
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