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Vintage Telephony and Telecomms Vintage Telephones, Telephony and Telecomms Equipment |
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25th Aug 2020, 7:45 pm | #1 |
Triode
Join Date: Jun 2015
Location: Ipswich, Suffolk, UK.
Posts: 49
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Tele 740 original use?
Hi all.
I have recently purchased a Tele 740 to use an an internal extension on a Plan 105. It got me wondering what the original use of this phone was. As you can see is has 4 buttons marked 1 - 4. These individually latch if off-hook & are restored when going on-hook. The phone was connected with an 18-core cable which has sadly been cut off. 15 cores are in use. Additional terminal blocks have been added so all cables can be connected. From what I can deduce from the wiring, the butons are be used to connect 1 of 4 lines to the phone at a time. These come in as isolated pairs. There is also a "signal" wire for each button which connects a common wire to a seperate output wire. Guess this was used maybe to light a lamp to show the line was active? There is an additional gravity switch which closes when off-hook. This seems to be wired so the signal wire mentioned above connects to another wire. Finally there is a thermistor which is simply in series with the bell. Any thoughts anyone? Thanks |
25th Aug 2020, 9:22 pm | #3 |
Triode
Join Date: Jun 2015
Location: Ipswich, Suffolk, UK.
Posts: 49
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Re: Tele 740 original use?
Hi Andrew - thanks for that.
Found another diagram - N4505 - which shows more details & explanations. Doesn't show the additional gravity switch & thermistor, but I think we are on the right track. Regards, Wayne |
26th Aug 2020, 9:59 pm | #4 | |
Octode
Join Date: Aug 2005
Location: Saltburn-East, Cleveland, UK.
Posts: 1,784
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Re: Tele 740 original use?
Quote:
In the Plan 2A diagram there is an "anti - tinkle" wire, my suspicion is that the Thermistor is fitted to prevent tinkle (remember that this phone would be used in conjunction with three other phones) instead of using a third wire for anti tinkle when dialling. The adiitional gravity switch may well have been for C wire signalling to a PMBX (with no recall), it's unlikely that it lit a lamp on other phones to indicate line in use as there is no lamp on your phone. I guess it will be a mystery as to the original use unless someone comes along who can confirm for definite which system the phone was used on, it may well even be a Plessey plan system variant. Regards Andrew |
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