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Old 17th May 2020, 9:51 pm   #1
beamcurrent
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Default Telephone exchange jackfield help

We are restoring a 1963 manual "control Line" telephone exchange as part of the BBC outside broadcast van.

The problem revolves round the jack cords which, to quote from the handbook, are "self retracting" Normally the cords would retract by gravity but in this installation there is no room for that. I visualise some sort of coiling arrangement, there is only about 6 inches under the desk top for this.

So the question is was there a "standard" device for this or did Pye make their own??

The telephone control line system is better known as magneto ringing and the panel has a set of dolls eye indicators for incoming calls.

More can be found on the projects website www.mcr21.org.uk
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Old 18th May 2020, 9:45 am   #2
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Default Re: Telephone exchange jackfield help

This looks like a great project. Several field exchanges has solutions for that, so the first one I think about is the US SB 22 PT
Here is a link with good pictures. The jack is made to accept ordinary 1/4" stereo plugs, but the wires has extremely small diameter. (2 mm??)
http://www.signalcenter.com/commo/eb...d1/3cord1.html

Another I know is the German one with shorter plugs, but a more normal wire diameter: https://www.finn.no/bap/forsale/ad.h...kode=155353583

(The seller in this deactivated ad has tried to sell a number of these for some time, and may have more of them stored. )

dsk

PS How many units do you need for this project (no of coils)? DS

Last edited by dagskarlsen; 18th May 2020 at 10:06 am. Reason: adding info
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Old 18th May 2020, 3:53 pm   #3
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Default Re: Telephone exchange jackfield help

Quote:
there is only about 6 inches under the desk top for this.
Was there a hole in the desk?
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Old 18th May 2020, 3:54 pm   #4
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Default Re: Telephone exchange jackfield help

Or did they go sideways with a spring and pully?
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Old 19th May 2020, 9:56 am   #5
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Default Re: Telephone exchange jackfield help

There are 15 cord retraction units closely spaced there are no holes and beneath there are amplifiers and power supplies.

The American device in the first link by dsk is the sort of principle I visualise, but with a jack at both ends of the device.

Pye, who made the OB vans, would have needed in total 150 of these so may have made them in their own factory, or was there a GPO unit that they could have used back in 1963?
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Old 19th May 2020, 12:12 pm   #6
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Default Re: Telephone exchange jackfield help

I wondered about the GPO/POT PMBX4, but when looking for that I found this which looks much more likely:-

https://switchboard-uk.tumblr.com/po...-manual-branch

Quote:
The cords are mounted in spring-loaded cassettes rather than hanging on weighted pulleys.
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Old 19th May 2020, 3:37 pm   #7
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Default Re: Telephone exchange jackfield help

That looks to be just the right sort of thing, I rather think finding some spare cassettes will be difficult, but at lease we know what we are looking for and it did exist!

Thanks very much for the link.

Brian
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Old 19th May 2020, 6:21 pm   #8
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Default Re: Telephone exchange jackfield help

Looks better than my exsamples.

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Old 20th May 2020, 8:57 am   #9
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Default Re: Telephone exchange jackfield help

Could this website yield some more information?

https://www.thg.org.uk/
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