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Old 12th May 2018, 10:07 pm   #1
Toothy Chris
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Default Puzzle - What was this giant jack plug used for?

I have been rummaging through an old collection of mostly Bakelite mains connectors/adaptors, which came from my Grandparents' house. In there was a cable, with a Bulgin 8-pin on one end, and a massive jack plug on the other end.

Can anyone suggest what this jack might have been used for?

The cable is 2-core brown/blue low-current mains cable, but I'm not convinced this kind of connector could have been used for mains, could it?

The big jack plug is quite heavy, being mostly brass and Bakelite, and seems to have no mechanism to hold it into whatever it went into. Markings on the brass part are:

404 PX61/5

And inside the Bakelite (?) cover the markings are:

PX/PX BA/2

And as you can see from the coin, this jack is much larger than a normal 1/4 inch jack.

Many thanks,

Toothy Chris
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Old 12th May 2018, 10:18 pm   #2
TonyDuell
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Default Re: Puzzle - What was this giant jack plug used for?

The plug looks like a Post Office Plug 404 (hence the number moulded into it), and would originally have been designed for use on the telephone system. But I doubt very much the cable or Bulgin socket was (offiicially) used for telephones.

It wouldn't have been used for mains.
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Old 12th May 2018, 11:06 pm   #3
OscarFoxtrot
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Default Re: Puzzle - What was this giant jack plug used for?

I really hope it wouldn't have been used for mains.

PX61/5 may mean made by Phoenix Telephones, Hendon, in May 1961.
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Old 12th May 2018, 11:19 pm   #4
Graham G3ZVT
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Default Re: Puzzle - What was this giant jack plug used for?

http://www.britishtelephones.com/plugs1.htm
Yes, a PO No 404
At a guess it might have connected an early telephone answering machine to the line.
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Old 12th May 2018, 11:31 pm   #5
Hartley118
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Default Re: Puzzle - What was this giant jack plug used for?

ISTR plugs like this being used to connect the operator's headset on the manual side of the exchange.

Back in the day, if the subscriber could persuade the PO that a plug-in phone was needed, the supplied plug was also like this.

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Old 13th May 2018, 6:33 am   #6
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Default Re: Puzzle - What was this giant jack plug used for?

I believe that they were also used on some aircraft headsets.
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Old 13th May 2018, 9:23 am   #7
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Default Re: Puzzle - What was this giant jack plug used for?

Back in the day, ISTR that if you had plug in phones, you also had to have a permanently connected separate bell set.
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Old 13th May 2018, 9:53 am   #8
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Default Re: Puzzle - What was this giant jack plug used for?

Can I suggest the mods move this thread to the Vintage Telephony section? Probably elicit some very experienced responses over there.
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Old 13th May 2018, 10:34 am   #9
M0FYA Andy
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Default Re: Puzzle - What was this giant jack plug used for?

Although of similar size, I don't think the aircraft headset type is identical to the PO404 type.
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Old 13th May 2018, 4:30 pm   #10
McMurdo
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Default Re: Puzzle - What was this giant jack plug used for?

I have a fair quantity of these and matching sockets, they plugged into the wall socket from the side.
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Old 13th May 2018, 7:39 pm   #11
philthespark
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Default Re: Puzzle - What was this giant jack plug used for?

Definitely a gpo type plug, there could be loads of reasons why it has the Bulgin connector on the other end, one possibility is it could have been made as a test adaptor by someone. My mate and I have loads of weird and wonderful leads we've made up over the years, sometimes we'll try and guess what some of each others leads connect to.
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Old 13th May 2018, 7:51 pm   #12
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Default Re: Puzzle - What was this giant jack plug used for?

If all 4 conductors of the jack plug were connected, I'd agree with Rambo that it was the line cable for an early answering machine. It could still be that, if the two "spare" pins are joined inside the plug (they would have been for the series-wired bell circuit, but the machine could have had its own ringing capacitor to supply the ring-detect relay coil).

Might be worth searching up old answering machines and seeing if any of them used a Bulgin connector for the telephone line?

Or it could have been intended for use with some long-since-lost home-made device, in which case we may never know .....
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Old 13th May 2018, 9:59 pm   #13
Toothy Chris
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Default Re: Puzzle - What was this giant jack plug used for?

Thanks to all who identified this as a Post Office 404 connector. Looking at the pictures of these, I can confirm this is what I have.

The suggestions regarding an answering machine may also be spot on, as my Grandfather was a very early adopter of an 'Ansafone', for his London based cloth business. I donated the Ansafone to a Museum some time, and to honest I can't remember if it had a bulgin connector on it. I looked at the photos I have, but can't see anything obvious.

Having said that, I do seem to remember that the handset used a Bulgin connector on the end of the cable.

For those interested in the Ansafone you will find a thread on here from several years ago, talking about this. And for those interested in the contents of the tape, you can search for "Answerphone Messages from c.1960" on Youtube.


Chris

P.S. The Bulgin connector does not have any of the other pins connected, or shorted.
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Old 13th May 2018, 10:06 pm   #14
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Default Re: Puzzle - What was this giant jack plug used for?

the plug 404 was used in conjunction with the jack 65 to provide telephone service over a number of rooms. the line in was 2 wires and these were extended to each socket.there was a rhyme for the wiring. in on 2 and 3 out on 2 and 4 with a strap between the 3 and the 4a or some such.
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Old 13th May 2018, 10:18 pm   #15
julie_m
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Default Re: Puzzle - What was this giant jack plug used for?

Quote:
Originally Posted by Toothy Chris View Post
P.S. The Bulgin connector does not have any of the other pins connected, or shorted.
No; but if the lead really was for making just a 2-wire connection to the phone line via that type of plug, I would expect to see two of the jack plug terminals strapped together to complete the ringing circuit. Otherwise, no phones would ring as long as the answering machine was plugged in -- unless they used non-standard wiring, or the machine did not support manual override; neither of which hypotheses is entirely implausible.
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Old 13th May 2018, 10:30 pm   #16
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Default Re: Puzzle - What was this giant jack plug used for?

When I was a student in the 1960's the telephone in the students' union that officials of the student societies could use, was kept locked in a cupboard and had to be signed out to use it. It had a plug like that to allow it to be used in the only socket, located in a corridor where its user could be seen from the office. Later, I saw one in use at a friend's parent's house. They had a bell mounted in the hall and sockets in several rooms, but only the one phone. I wonder if it was cheaper than having individual extensions, given that in that pre-privatisation era, domestic customers had to rent their equipment from the post office.
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Old 13th May 2018, 10:32 pm   #17
space charge
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Default Re: Puzzle - What was this giant jack plug used for?

it appears to have been an experimental arrangement . if a telephone person did it I would expect some type of tele cable to have been used not mains cable, the again perhaps it was used to test a system ie in some hospitals there were numerous sockets.
regards ei7ka
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