TELECOM 247

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news:8b8a3b8a-e02d-404a-b16a-d231440406df@e25g2000prg.googlegroups.com...

I suspect that the answer lies back many, many years - my copy of Telephony
Vol 1, Herbert and Proctor, first published in 1934 says that speech quality
using carbon granule microphones is better with 40v than 24v. Why -50v I
really dont know, but the UK has used -50v since time immemorial and since
strowger type exchanges had a nice big stable power supply of -50v
everything to follow was designed to use it. Even with relatively modern
equipment the -50v central supply, already in place, was convenient, very
secure, and was often used to power rack convertors to provide 12v, 5v, etc.
supplies to specific equipment.


Peter