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Old 22nd Jul 2021, 8:48 am   #1
Dave Moll
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Default Shared Service (Party Line) emulation

I have a pair of telephones 312 that I would like to use to create a demonstration of shared service (party line) working, connecting to two extensions of a PABX. Has anyone ever designed an interface to sit between the telephones and the lines to enable the telephones to be used as though they were connected via shared service?
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Old 22nd Jul 2021, 1:11 pm   #2
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Default Re: Shared Service (Party Line) emulation

I am sure others with more knowledge will chip in but my recolection is that the two wires were connected in parallel for the speech circuit so that if one party is talking the other could listen in by simply lifting the receiver.
The ringing was selective by sending the ac ring voltage between one wire and earth, each party had their bell connected from one of the wires to a local ground spike, each party used a different wire.

Which reminds me of the story, apocriphal I am sure, about the lady who claimed to have a psychic dog, it would howl just before the telephone rang.
Turns out she used to tie her dog to the local earth spike by a metal chain. The earth spike was in dry ground and a poor earth. When the ring voltage was sent the chain connected to the earth spike gave the dog a shock, who then howled and wet himself, the wee wet the ground and completed the earth and the telephone rang.

Peter
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Old 22nd Jul 2021, 2:20 pm   #3
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Default Re: Shared Service (Party Line) emulation

Yes, the phones (designated "X" and "Y") were indeed wired with their speech circuits in parallel as Peter describes, though the "Y" is connected with "A" and "B" legs reversed to achieve the ringing between the appropriate leg and earth.

In order to make a call, the handset is lifted and a check is made that the other party is not engaged in a call. If the line is free, the "call exchange" button is pressed to obtain a dial tone and the outgoing call then proceeds as normal.

On receiving a call (with ringing on ones appropriate ringer), I seem to recall that one simply had to lift the handset to be connected to the caller. I don't recall having to press "call exchange" in this instance, though it would probably simplify the circuitry if one did.

My question was really to avoid "reinventing the wheel" if someone has already designed a circuit, either by the traditional GPO way using relays or with solid-state electronics, before I try to work out something to make a pair of telephones behave as described above.

And yes, the (no doubt apocryphal) story about the "psychic" dog does crop up from time to time, and is quoted in one of the early issues of the Telecommunications Heritage Journal.
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Old 22nd Jul 2021, 3:08 pm   #4
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Default Re: Shared Service (Party Line) emulation

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On receiving a call (with ringing on ones appropriate ringer), I seem to recall that one simply had to lift the handset to be connected to the caller.
Aye, and if the other party just happened to lift their handset to make a call, they would trip the ring and answer the incoming call to their neighbour - oops!

The psychic dog is no doubt an early urban myth, but..
When investigating ringing problems, many a subscriber, on being advised to pour water on the earth spike, thought the engineer was having a laugh and trying to wind them up.
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Old 22nd Jul 2021, 3:52 pm   #5
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Default Re: Shared Service (Party Line) emulation

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but..
When investigating ringing problems, many a subscriber, on being advised to pour water on the earth spike, thought the engineer was having a laugh and trying to wind them up.
You need to read Prof R V Jones' autobiography.

One incident in it involves a telephone in an apartment shared by young engineers, a rather senior scientist with a diabolical sense of humour and a candlestick telephone impersonating an 'engineer at the exchange'.

A second incident involving a series of tortoises of graduated sizes, and a visiting American scientist isn't radio-related. but does serve to provide some triangulation on the sorts of persons protecting us in WWII.

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Old 22nd Jul 2021, 5:55 pm   #6
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Default Re: Shared Service (Party Line) emulation

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Yes, the phones (designated "X" and "Y") were indeed wired with their speech circuits in parallel as Peter describes, though the "Y" is connected with "A" and "B" legs reversed to achieve the ringing between the appropriate leg and earth.

In order to make a call, the handset is lifted and a check is made that the other party is not engaged in a call. If the line is free, the "call exchange" button is pressed to obtain a dial tone and the outgoing call then proceeds as normal.

On receiving a call (with ringing on ones appropriate ringer), I seem to recall that one simply had to lift the handset to be connected to the caller. I don't recall having to press "call exchange" in this instance, though it would probably simplify the circuitry if one did.

My question was really to avoid "reinventing the wheel" if someone has already designed a circuit, either by the traditional GPO way using relays or with solid-state electronics, before I try to work out something to make a pair of telephones behave as described above.

And yes, the (no doubt apocryphal) story about the "psychic" dog does crop up from time to time, and is quoted in one of the early issues of the Telecommunications Heritage Journal.
You did not need to press the 'Call Exchange' button when answering the telephone. Normally there was battery on both the A & B legs when normal - via the two line circuits 'L' relays. Pressing the 'Call Exchange' button operated the L relay for the appropriate line which then operates the K relay for that line circuit and the extended 'loop' then seizes a group selector which returns an earth to hold the K relay (which has connected the meter appropriate to that calling line). Call then progresses as normal. This setup was introduced just after WW2 with the introduction of the Tele 310 & Bellset No 41(to prevent bell tinkle when the other party was dialling). However with the introduction of the Thermistor a couple of years later, the Tele 310's in the stores were modified to Tele 312's and the BS41's sold off which is why they are so common on eBay and Tele 310's are so rare! This system was known as 'Shared Service, Separate Metering' whereas previously there was an earlier automatic system known as 'Shared Service, Common Metering' often seen on older N diagrams. Often disputes between parties as to made the calls! Sale of this system was discouraged but lack of copper after WW2 forced the 'Separate Metering' version being introduced.

Must be nearly ten years ago, we had some variations of party lines working on CNet. With one setup there were just two phones on the same pair each with its own number and they were rung with distinctive codes. In fact we replicated the system used in New Zealand on UAX13s where there were up to six phones on the line, one with normal double beat ringing, and the others were rung by codes - Morse letters repeated A (short long) , D (Long short short), M (long long), R (short long short) and S (short short short).
It was even possible to dial any of the other numbers on the same line . However as CNet has no metering, the setup didn't use the 'Call Exchange' button.

But it should be possible to knock up a small 'box' to go between two PBX extensions that needed the 'Call Exchange' button to initiate a call and to ring the two phone individually via one leg to earth.

With reference to 'odd situations' with party line - this is one I know to be true as I was there! Just after the conversion from a CBS2 exchange to a UAX13 at Tarporley in Cheshire, the firemen from the 'retained' fire station kept getting call outs. It took a while until we tracked the problem down. The fire-bells were operated by the 'WRU' (Who are You) mechanism being operated on the teleprinter in the fire station after the message giving details of the fire location had been sent by Fire Service HQ in Chester. What was happening here was the party line earth from the Tele 312 had been connected to the fire-bell earth (fire-bells were a single wire to earth system). The problem was when one of the firemen made a call by pressing the 'Call Exchange' button - the 50 volts from the phone line was finding a shorter route to earth via the other fire-bells (all connected between the fire bell single wire & earth) rather than via the local earth! A very interesting fault.
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Old 22nd Jul 2021, 8:20 pm   #7
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Default Re: Shared Service (Party Line) emulation

Long after party lines there were (may be still are) other "earth start" lines, and when I encountered them they were a nuisance to test, they needed a PABX that supported that line type, and I never really understood why they were there.

I don't think meter pulses were involved (another service that required a local earth connexion), but I suppose historically it might have been a factor.
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Old 22nd Jul 2021, 9:15 pm   #8
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Default Re: Shared Service (Party Line) emulation

Seeing the mention of meter pulses, I should add that I am not intending to include any emulation of metering in my setup - at least not in the first instance. Maybe I'll include simple counters of outgoing calls at a later stage to demonstrate which line was used by each telephone.
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Old 22nd Jul 2021, 9:38 pm   #9
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Default Re: Shared Service (Party Line) emulation

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Originally Posted by 198 kHz View Post
Quote:
Originally Posted by Dave Moll View Post

On receiving a call (with ringing on ones appropriate ringer), I seem to recall that one simply had to lift the handset to be connected to the caller.
The psychic dog is no doubt an early urban myth, but..
When investigating ringing problems, many a subscriber, on being advised to pour water on the earth spike, thought the engineer was having a laugh and trying to wind them up.
I would not laugh at the dog, theory. Way back in the 70 I used to see a few reports of "miracle" cures of this sort in certain Sunday papers. Up north (in the highlands) bad earth and earth leakage ) were things we encountered daily. Water on earth spikes- we were taught about this as apprentices. bell tinkle- common cause was maims leakage. I've actually measured circa 150vAC across persons rear gate. I've fitted an external plan 10x (5/7) in a scrap yard and had to bury an old car radiator deep in the slate,( to pick up the watercourse)and drive an earth spike through it to get a decent earth.
One thing that was hard to impart to UG staff when exchanges became Auto and ringback was available was that it didn't work on SS . A successful test needed an operator to ring the two numbers and ensure that the correct number rang as the equipment only rang back the number that applied the earth. All part and parcel of being a mixed Subs app installer/Mtxe man( or boy).
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Old 22nd Jul 2021, 10:08 pm   #10
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Default Re: Shared Service (Party Line) emulation

I seem to remember there was a procedure involving the Operator if a subscriber needed to call the other party on their line. How did this work exactly, and were they billed for the call?
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Old 23rd Jul 2021, 7:11 pm   #11
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Default Re: Shared Service (Party Line) emulation

Not that I can add anything about the way of simulating one, but I do remember that when I was a child, my parents had such a shared line. They hated it, because the people it was shared with were quite careless and often left their phone off hook, and it was quite a way up the village to them to get them to put it back properly. Not only that, but they weren't careful about checking when the line was in use, and would regularly interrupt my parents calls. I honestly can't remember whether there was ever a non-shared line before we moved in the early seventies.
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Old 23rd Jul 2021, 8:04 pm   #12
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Default Re: Shared Service (Party Line) emulation

Hi, I tried experimenting to make a shared service emulator using relays in each station "line circuit" that were held via the loop after the "call exchange" button was depressed, this seemed satisfactory for outgoing calls until I began to look at the incoming ringing and drew up a couple of other designs which weren't very successful.

I had thought about going back to the drawing board, however many other factors of life got in the way, as is often the case. If I, or anyone else, make any progress, it would be interesting to see the resulting circuit.

Andrew
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Old 23rd Jul 2021, 8:11 pm   #13
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Default Re: Shared Service (Party Line) emulation

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One thing that was hard to impart to UG staff when exchanges became Auto and ringback was available was that it didn't work on SS . A successful test needed an operator to ring the two numbers and ensure that the correct number rang as the equipment only rang back the number that applied the earth. All part and parcel of being a mixed Subs app installer/Mtxe man( or boy).
Try getting a Kelly’s subbie to even understand that……
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Old 23rd Jul 2021, 8:46 pm   #14
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Default Re: Shared Service (Party Line) emulation

In the 60s my parents' house was on a 'party line'. Not sure whether this was a specific feature of the party-line implementation but it was - to paraphrase Tom Jones - 'not unusual' to hear the BBC Light-Program in the background of your calls.

Perhaps "Noises-off" should be included in any party-line simulation??

[In the very-early-70s we had oil central-heating installed and the installers snapped the earth-wire while winching the 1000-gallon oil tank into place. Meaning no-ding-a-ling! The GPO said it would be at least a week for someone to come out and investigate [even though I told them precisely what the problem was]. So I 'borrowed' a length of Don10 cable and a couple of the Thermite-powered line-jointers from the school CCF signals-unit and had the problem fixed the next day].
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Old 23rd Jul 2021, 9:06 pm   #15
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Default Re: Shared Service (Party Line) emulation

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Hi, I tried experimenting to make a shared service emulator using relays in each station "line circuit" that were held via the loop after the "call exchange" button was depressed, this seemed satisfactory for outgoing calls until I began to look at the incoming ringing and drew up a couple of other designs which weren't very successful.
It's good to know that you had a go at this. Apart from anything else, it helps to reassure me that wanting to do so isn't entirely crazy!

I find it interesting that at the practical level you hit the snag that I have been envisaging in thinking through what is needed - which is why I commented earlier that emulating incoming calls might be easier if it involved pressing "call exchange", as this would seem to enable incoming calls to be handled in a similar way to outgoing. On incoming, all I can envisage is that the ringing current itself will need to engage a relay which in turn connects the exchange line carrying the ringing current between the appropriate leg and earth and enables the making of a loop at the appropriate station to engage the connecting relay - which is where I start to come unstuck.

My thought experiment for outward calling goes as follows:

In the idle state, each leg of the subscriber line is connected via a relay coil to battery. The other end of the relay is connected to earth.

When a subscriber goes off-hook and depresses "call exchange" (CE), this connects that subscriber's leg to earth and actuates the above relay which first connects itself (via a relay powered by line current) to a supply to keep itself engaged once CE is released, and disconnects the subscriber line from the relay and connects it to the exchange line. Both these relays probably need to be delayed-release so that they don't release during either the above switching or (for the one powered by line current) during dialling.

Once the subscriber clears down, the line-powered relay then releases, in turn releasing the first relay and everything returns to the idle state.

In theory, would this work?

To be honest, I can't yet get my head round what is needed for handling incoming!
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Old 23rd Jul 2021, 9:13 pm   #16
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Default Re: Shared Service (Party Line) emulation

Two houses where I lived when I was up in North Wales had party lines one was the same as the type described here but the other one was different. The phone was connected to a "box" which was connected to the line. I suspect the outgoing and incoming audio were modulated onto carriers which allowed one overhead line to carry more than one than one number. Both houses were out in the wilds with only one or two houses in the vicinity.

This box had to be replaced as it failed while I was living at the house. It's possible that the original didn't like 10W of 2m radio next to it.

Keith
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Old 24th Jul 2021, 12:27 am   #17
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Default Re: Shared Service (Party Line) emulation

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Two houses where I lived when I was up in North Wales had party lines one was the same as the type described here but the other one was different. The phone was connected to a "box" which was connected to the line. I suspect the outgoing and incoming audio were modulated onto carriers which allowed one overhead line to carry more than one than one number. Both houses were out in the wilds with only one or two houses in the vicinity.

This box had to be replaced as it failed while I was living at the house. It's possible that the original didn't like 10W of 2m radio next to it.

Keith
DACS Digital access carrier system
https://en.wikipedia.org/wiki/Digita...carrier_system
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Old 24th Jul 2021, 10:07 am   #18
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Default Re: Shared Service (Party Line) emulation

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Two houses where I lived when I was up in North Wales had party lines one was the same as the type described here but the other one was different. The phone was connected to a "box" which was connected to the line. I suspect the outgoing and incoming audio were modulated onto carriers which allowed one overhead line to carry more than one than one number. Both houses were out in the wilds with only one or two houses in the vicinity.

This box had to be replaced as it failed while I was living at the house. It's possible that the original didn't like 10W of 2m radio next to it.

Keith
DACS Digital access carrier system
https://en.wikipedia.org/wiki/Digita...carrier_system
Or more likely its predecessor the WB900 system - audio channel plus one analogue carrier channel. See http://www.rastall.com/wb900.htm
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Old 24th Jul 2021, 4:20 pm   #19
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I seem to remember there was a procedure involving the Operator if a subscriber needed to call the other party on their line. How did this work exactly, and were they billed for the call?
IIRC, the procedure was to call the operator and say "party" if wishing to speak with the other party on the shared line.
There was no charge for this call.

Before making any other call one had to lift the handset and ensure that no conversation was underway.
If it was, one had to replace the handset and wait, except in the case of an emergency such as fire or sudden illness. In that case interrupting the existing call was acceptable by saying "THIS AN EMERGENCY, PLEASE REPLACE THE RECEIVER" 999 could then be called in the usual way.

I recall a public information film shown to school children, on how to call the emergency services, which included what to do in case of a party line.
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Old 24th Jul 2021, 6:29 pm   #20
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Default Re: Shared Service (Party Line) emulation

There also was a scene in a Margaret Rutherford film which, from memory went like this.

I know this is a party-line, but I need to call the police.
Don't take that tone with me young man,
Indeed I do have a crime to report.
Murder, murder most foul.
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