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abhi.15sep@gmail.com
 Post subject: Telephone CO supply
PostPosted: 2007-11-16 03:32:31
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Joined: 2007-11-16 03:32:31
why telephone offices have -48V sypply ?


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Ivor Jones
 Post subject: Telephone CO supply
PostPosted: 2007-11-16 13:56:03
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Joined: 2007-11-16 13:56:03
wrote in message
news:8b8a3b8a-e02d-404a-b16a-d231440406df@e25g2000prg.googlegroups.com
: : why telephone offices have -48V sypply ?

Its 50V actually, to power the exchange (not CO were British here)
equipment, why do you ask..?

Ivor


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Ivor Jones
 Post subject: Telephone CO supply
PostPosted: 2007-11-16 13:56:40
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Ivor Jones wrote in message
news:5q5lrnFu6qbgU1@mid.individual.net
: : wrote in message
: : news:8b8a3b8a-e02d-404a-b16a-d231440406df@e25g2000prg.googlegroups.com
: : : : why telephone offices have -48V sypply ?
: :
: : Its 50V actually, to power the exchange (not CO were
: : British here) equipment, why do you ask..?

Sorry that should of course read -50V :-)

Ivor


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steveybar
 Post subject: Telephone CO supply
PostPosted: 2007-11-16 16:58:31
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Ivor Jones wrote in message
news:5q5lrnFu6qbgU1@mid.individual.net...
> wrote in message
> news:8b8a3b8a-e02d-404a-b16a-d231440406df@e25g2000prg.googlegroups.com
> : : why telephone offices have -48V sypply ?
>
> Its 50V actually, to power the exchange (not CO were British here)
> equipment, why do you ask..?
>
> Ivor
>

Yes, Ive also always wondered why -50v dc, why not -25v or -75v or -100v or
.....?

And whilst we are at it, why is it a -ve value (-50v), and not a +ve value
(+50v) ?


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Peter Andrews
 Post subject: Telephone CO supply
PostPosted: 2007-11-16 17:46:43
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wrote in message
news:8b8a3b8a-e02d-404a-b16a-d231440406df@e25g2000prg.googlegroups.com...
> why telephone offices have -48V sypply ?

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


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Mike
 Post subject: Telephone CO supply
PostPosted: 2007-11-16 18:16:33
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Joined: 2007-11-16 18:16:33
On Fri, 16 Nov 2007 16:58:31 -0000, steveybar
wrote:

>
>Ivor Jones wrote in message
>news:5q5lrnFu6qbgU1@mid.individual.net...
>> wrote in message
>> news:8b8a3b8a-e02d-404a-b16a-d231440406df@e25g2000prg.googlegroups.com
>> : : why telephone offices have -48V sypply ?
>>
>> Its 50V actually, to power the exchange (not CO were British here)
>> equipment, why do you ask..?
>>
>> Ivor
>>
>
>Yes, Ive also always wondered why -50v dc, why not -25v or -75v or -100v or
>.....?

No idea, something historical and probably thought of in the days
before there was even a Post Office Electrical Engineers Journal

>And whilst we are at it, why is it a -ve value (-50v), and not a +ve value
>(+50v) ?

Because the +ve is earthed

Now ask why.......

:)


--


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steveybar
 Post subject: Telephone CO supply
PostPosted: 2007-11-16 18:45:07
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Joined: 2007-11-16 18:45:07
Mike wrote in message
news:2vqdnYxTO44cQ6DanZ2dnUVZ8tHinZ2d@pipex.net...
>
> On Fri, 16 Nov 2007 16:58:31 -0000, steveybar
> wrote:
>
>>
>>Ivor Jones wrote in message
>>news:5q5lrnFu6qbgU1@mid.individual.net...
>>> wrote in message
>>> news:8b8a3b8a-e02d-404a-b16a-d231440406df@e25g2000prg.googlegroups.com
>>> : : why telephone offices have -48V sypply ?
>>>
>>> Its 50V actually, to power the exchange (not CO were British here)
>>> equipment, why do you ask..?
>>>
>>> Ivor
>>>
>>
>>Yes, Ive also always wondered why -50v dc, why not -25v or -75v or -100v
>>or
>>.....?
>
> No idea, something historical and probably thought of in the days
> before there was even a Post Office Electrical Engineers Journal
>
>>And whilst we are at it, why is it a -ve value (-50v), and not a +ve value
>>(+50v) ?
>
> Because the +ve is earthed
>
> Now ask why.......
>
> :)

OK - why.....

and why not have used +50v and earthed the -ve ?


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Steve H
 Post subject: Telephone CO supply
PostPosted: 2007-11-16 19:19:07
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Joined: 2007-11-16 19:19:07
steveybar wrote:
> Mike wrote in message
> news:2vqdnYxTO44cQ6DanZ2dnUVZ8tHinZ2d@pipex.net...
>> On Fri, 16 Nov 2007 16:58:31 -0000, steveybar
>> wrote:
>>
>>> Ivor Jones wrote in message
>>> news:5q5lrnFu6qbgU1@mid.individual.net...
>>>> wrote in message
>>>> news:8b8a3b8a-e02d-404a-b16a-d231440406df@e25g2000prg.googlegroups.com
>>>> : : why telephone offices have -48V sypply ?
>>>>
>>>> Its 50V actually, to power the exchange (not CO were British here)
>>>> equipment, why do you ask..?
>>>>
>>>> Ivor
>>>>
>>> Yes, Ive also always wondered why -50v dc, why not -25v or -75v or -100v
>>> or
>>> .....?
>> No idea, something historical and probably thought of in the days
>> before there was even a Post Office Electrical Engineers Journal
>>
>>> And whilst we are at it, why is it a -ve value (-50v), and not a +ve value
>>> (+50v) ?
>> Because the +ve is earthed
>>
>> Now ask why.......
>>
>> :)
>
> OK - why.....
>
> and why not have used +50v and earthed the -ve ?
>
>
>
>
To prevent electrolytic corrosion of the cables.

Steve H


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