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Vintage Telephony and Telecomms Vintage Telephones, Telephony and Telecomms Equipment |
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18th Jul 2014, 10:37 am | #41 |
Triode
Join Date: Jul 2014
Location: Essex, UK.
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Re: GPO 746 wiring query 2-wire
Presumably this could go between T5/T6 or T6/T7 in place of a strap?
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Craggus2000 "If it ain't broke, break it and make it better" |
18th Jul 2014, 10:43 am | #42 |
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Re: GPO 746 wiring query 2-wire
If your phone is wired as per post #25, that will be OK.
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18th Jul 2014, 11:55 am | #43 |
Dekatron
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Re: GPO 746 wiring query 2-wire
I think you only want the thermistor in series with the bell, not the receiver circuit, therefore I would put it either between T4 and T5 or between T16 and T17. Looking at the N846 wiring diagram, T5 is shorted to T6 when the handset is on its cradle, thus nullifying the thermistor.
I would have thought that a thermistor in series with the receiver (as it would be between T6 and T7) might reduce volume, given that it would be at its maximum resistance at the low current produced by the speech.
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18th Jul 2014, 12:00 pm | #44 |
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Re: GPO 746 wiring query 2-wire
The link I posted in post #32 suggests 16 to 17.
4 to 5 can't be used as the resistor is wired there according to post #25. As you say 5 to 6 is a no no as there are switch hooks contacts across these points. Likewise 6 to 7 which would put the thermistor in series with the receiver.
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18th Jul 2014, 4:02 pm | #45 | |
Hexode
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Re: GPO 746 wiring query 2-wire
Quote:
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18th Jul 2014, 7:57 pm | #46 |
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Re: GPO 746 wiring query 2-wire
It was an official BT mod, but only for Trimphones which used an electronic ringer. For other phones the recommended mod was to fit a 4000 ohm bell.
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Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
18th Jul 2014, 8:56 pm | #47 | |
Dekatron
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Re: GPO 746 wiring query 2-wire
Quote:
When you add the 1u8 capacitor in series the impedance becomes 1598 -j1466, or 2169 ∟-42.5° Z. All this for 25Hz. I've never had any problems not fitting a resistor.
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24th Jul 2014, 10:40 pm | #48 |
Triode
Join Date: Jul 2014
Location: Essex, UK.
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Re: GPO 746 wiring query 2-wire
Just thought I'd say I've not dropped off... Just the phone is now in pieces being stripped down, cleaned and polished...
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Craggus2000 "If it ain't broke, break it and make it better" |