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Vintage Telephony and Telecomms Vintage Telephones, Telephony and Telecomms Equipment

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Old 10th Dec 2011, 6:27 pm   #1
alanglobal
Retired Dormant Member
 
Join Date: Oct 2011
Location: Manchester
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Default Can anyone identify this switch?

Hello all,

My Dad came to visit today and brought along a Grey 746, so it was off with the case and have a nosy inside. It has an unusual switch attached to the chassis - a clear plastic cover containing switch contacts which seems to operate when the pick-up is depressed or released. The wires attached to it had been disconnected from any terminals. The picture attached should show it more clearly than I can describe.

Could anyone identify its purpose and how to wire it?

thanks in advance,

Alan
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Old 10th Dec 2011, 7:17 pm   #2
Chipmunk
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Join Date: Mar 2007
Location: Southampton, Hampshire, UK.
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Post Re: Can anyone identify this switch?

Hi Alan, looks to be a 1/DSP/1242 contact set at a guess, used for auxiliary connections on a tele 710 (according to the N diagram, on Sam Hallas's excellent site here: http://www.samhallas.co.uk/repositor.../0000/N848.pdf )

These would mainly have been used with plan systems I would imagine, where extra cradle contacts were needed. It really wouldn't be of any use on a direct exchange line. Possibly this phone may have come from a 'c wire signalling system' where an extra pair of contacts on the hookswitch were needed.

You could leave it in place and just connect the terminals to any spare connections (T11 to T15 are usually spare on the 746).
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Old 10th Dec 2011, 8:32 pm   #3
val33vo
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Default Re: Can anyone identify this switch?

In the era of this type of telephone ( 1970,s ) telephones and exchange equipment was more or less hand built to suit the application desired so what use this extra set of contacts would have been put to is open to guess

My thoughts would be perhaps an extension off a PMBX or PABX with some unusual call facilities

The 746,s had any amount of extra,s that could be fitted to suit reqirements and the M.O.D had some stuff built for them exclusively, I well remember stripping out an experimental strowger weather reporting system which had literaly been built on the spot ( it did not function satisfactorarilly )


regards

val33vo
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Old 10th Dec 2011, 9:47 pm   #4
AndiiT
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Default Re: Can anyone identify this switch?

Hi,
It appears that there is also an "Auxiliary" switch fitted (between the switch hook bracket) and I would hazard a guess that this phone was originally used as an extension to a Manual PBX, as val33vo already suggests, with 'C' wire signalling such as one of the PMBX 2 or perhaps PMBX 4 switchboards.

The auxiliary gravity switch was wired in parallel with the auxiliary button when used on these switchboards to enable signals for supervisory indicators, such as lamps and/or buzzers, to be sent along the C Wire and Earth, separating them from the A and B pairs used for transmission.

Regards

Andrew
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