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Old 28th Jul 2021, 4:44 pm   #23
Join Date: Jul 2007
Location: Flintshire, UK.
Posts: 623
Default Re: Shared Service (Party Line) emulation

Originally Posted by broadgage View Post
There was another system, sometimes incorrectly called a party line, but more properly known as a "call concentrator"

Consider a village with 6 telephone subscribers and connected to the distant exchange by a cable or overhead line route with 10 circuits so as to allow for expansion.
In time, more than 10 telephone lines might be required. To avoid costly replacement of the existing cables, a concentrator could be installed. This was in effect a miniature and fully automatic exchange that connected one of the 10 existing lines to whichever telephone was in use.
This allowed the existing 10 lines to serve several times that number of customers, provided that only 10 of these customers used the phone at the same time.
If two subscribers WITHIN the village wished to talk, the concentrator would connect them to each other without use of any of the ten lines to the distant exchange.
The equipment was often installed in a secure cabinet, in the village public phone box.
I think you are referring to a 'Line Connector' which was a form of concentrator. There were two versions introduced c1959/60 - the Line Connector No 1 and guess what - the Line Connector No 2 !

The No 1 system had two pairs of wires back to the exchange and could have up to ten subscribers connected. The subscribers were for all intents and purposes of a direct pair of wires to the exchange and were charged as such. This system didn't last very long as if a subscriber on the LC1 called another on the same LC!, it blocked the system up (the connection was made at the exchange). The subscribers end was a pole mounted unit with a jack in 2000 type relay set. Unusually it had no battery to operate at the pole, all the relays were 'remnant' relays operated by burst of current from the exchange and released by another burst.

The Line Connector 2 was bigger with four pairs between the LC and the exchange and up to 22 subs on their own circuits off the LC.. They were mounted in double door roadside cabinets which also contained several small 12 volt battery to produce the 48 volt to power the LC. They used uniselectors to do the line selection. These were charged over the pairs back to the exchange. These survived longer in use - last ones I remember were in the late 1970's here in NE Wales. The LC2 didn't suffer the blocking problem unless four subs on same cabinet rang each other at the same time - rarely happened. I'm lucky enough to have an LC1 acquired many years ago. There is a preserved railway with a working LC2.

It wasn't the first system of its type. There was the Country Satellite eXchange (CSX in GPO abbreviations) These were 10 lines with one pair back to a manual exchange. Again they used a high/low current in various directions to connect the call and a call could be setup up between two lines on the same unit but was still via the answering and calling cords on a cord circuit at the manual exchange. I've only ever seen one in service on a small scottish island - Kerrera - parented on the auto-manual board at Oban in the 1970's. At that time there were three others in the Highland which had their own exchange names but soon were replaced. I'm not aware of any CSX survivors. Interesting the first 'automatic' equipment in the UK public network was installed in the 1880's allowing five subs to use a single pair much like the CSX system. Developed by Dane Sinclair then of the National Telephone Co but later on the board of Automatic Telephone Manufacturing many years later.
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