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Vintage Telephony and Telecomms Vintage Telephones, Telephony and Telecomms Equipment |
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16th Jul 2014, 11:02 am | #21 |
Triode
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Re: GPO 746 wiring query 2-wire
Re-done diagram now, so T14 and T15 and blue and green respectively...
Sorry...
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Craggus2000 "If it ain't broke, break it and make it better" |
16th Jul 2014, 11:27 am | #22 |
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Re: GPO 746 wiring query 2-wire
Looks spot-on as far as I can tell at a quick glance. Try it!
Did you see post 20? Nick |
16th Jul 2014, 1:13 pm | #23 |
Triode
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Re: GPO 746 wiring query 2-wire
Hi Nick,
Yeah I did. I'm not sure what C1 value is (can't see it at the mo). Although I thought it was supposed to be 0.9uF? But also was thinking it might be better to use a modern equivalent? Craig
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Craggus2000 "If it ain't broke, break it and make it better" |
16th Jul 2014, 1:14 pm | #24 |
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Re: GPO 746 wiring query 2-wire
Some phones had one 1.8uF, others had two 0.9uF in parallel, which is essentially the same thing. Yours will be the former.
No, the old cap will be fine. They were very good quality and don't seem to fail with age, even in phones that have been stored in awful conditions. Make use of it! Nick. |
16th Jul 2014, 1:30 pm | #25 |
Triode
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Location: Essex, UK.
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Re: GPO 746 wiring query 2-wire
OK! so assuming it's ok, Just linking T6 and T7 should solve it? (attached)
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Craggus2000 "If it ain't broke, break it and make it better" |
16th Jul 2014, 1:51 pm | #26 |
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Re: GPO 746 wiring query 2-wire
Yes, looks right. Try it and see. The nice thing about this kind of phone is that they're almost indestructable so you won't do any damage.
N. |
16th Jul 2014, 2:44 pm | #27 |
Triode
Join Date: Jul 2014
Location: Essex, UK.
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Re: GPO 746 wiring query 2-wire
Will give it a go tonight if i get a chance, and let you know...
Next step is to add a rotatone...
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Craggus2000 "If it ain't broke, break it and make it better" |
17th Jul 2014, 2:02 pm | #28 |
Triode
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Re: GPO 746 wiring query 2-wire
Ok, I re-wired the 746 last night to use the internal capacitor for ringing, as you said it was a 1.8uF. It works!
However, when replacing the phone on the hook (or just lifting and replacing at any time), a single strike of the bell is heard. Is this just a case of adjusting the bells or could there be something odd going on with the wiring?
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Craggus2000 "If it ain't broke, break it and make it better" |
17th Jul 2014, 2:21 pm | #29 |
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Re: GPO 746 wiring query 2-wire
Well done!
As for your single strike; that's absolutely normal. It's a good way of seeing if they're using a real phone in a film or TV programme. If it goes "ding" as the receiver is lifted or replaced, then it probably is a working phone as opposed to a sound-effects CD. The only problem you're likely to get with this wiring arrangement is if you use multiple dial phones on the same line, when you might get "bell tinkle" i.e. a series of strikes on the other phones' bells corresponding to each dial pulse. N. |
17th Jul 2014, 2:29 pm | #30 |
Triode
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Re: GPO 746 wiring query 2-wire
Thanks!
Is there any way to get around this with the phone wired as a 2-wire phone?
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Craggus2000 "If it ain't broke, break it and make it better" |
17th Jul 2014, 2:35 pm | #31 |
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Re: GPO 746 wiring query 2-wire
Not as far as I know, but some of the others are more expert than me, so see what they have to say.
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17th Jul 2014, 2:44 pm | #32 |
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Re: GPO 746 wiring query 2-wire
You could wire a Thermistor 1A/1 in series with the bell:-
http://www.samhallas.co.uk/collection/bits_706_4.htm Sorry, but I don't know what modern thermistor you can use, but someone on here will know.
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17th Jul 2014, 2:46 pm | #33 |
Triode
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Re: GPO 746 wiring query 2-wire
Ahh, Presumably if I install a rotatone (pulse to tone converter) in the phone I wouldn't get tinkle?
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Craggus2000 "If it ain't broke, break it and make it better" |
17th Jul 2014, 2:46 pm | #34 | |
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Re: GPO 746 wiring query 2-wire
Quote:
A GPO engineer probably would fob you off by saying that was to let you know the receiver was set down properly and so you wouldn't be charged any more for the call. And I bet more than one person has by happenstance had the stored charge exactly cancel the DC bias on the line, resulting in no "ting", and picked the receiver up and hung it up again! Bell tinkle is pretty much inevitable with two-wire phones and loop-disconnect dialling. The only cures are: three-wire system, shunting out all the bells in parallel while any phone is off the hook; four-wire system, series-wired bell chain, interrupted while any phone is off-hook; or DTMF.
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17th Jul 2014, 2:48 pm | #35 |
Triode
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Re: GPO 746 wiring query 2-wire
Ahh yes, I removed a pretty ropey looking 1A/1 from the phone when I first converted it, anyone know the modern equivalent?
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Craggus2000 "If it ain't broke, break it and make it better" |
17th Jul 2014, 2:50 pm | #36 |
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Re: GPO 746 wiring query 2-wire
Just because it looks ropey doesn't mean it's non-functional. Try it and see what happens.
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17th Jul 2014, 2:51 pm | #37 |
Triode
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Re: GPO 746 wiring query 2-wire
Need to see if I still have it though!
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Craggus2000 "If it ain't broke, break it and make it better" |
17th Jul 2014, 3:44 pm | #38 |
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Re: GPO 746 wiring query 2-wire
This would stop this 'phone causing bell-tinkle on other 'phones, as it is no longer sending loop-disconnect pulses onto the line. As far as I know, though, this won't stop other LD 'phones on the same same causing tinkle on this one.
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17th Jul 2014, 8:03 pm | #39 | |
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Re: GPO 746 wiring query 2-wire
Quote:
I may have a spare 1A/1 thermistor kicking around somewhere just send me a PM if you can't find your original thermistor. Andrew |
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17th Jul 2014, 10:26 pm | #40 | |||
Triode
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Re: GPO 746 wiring query 2-wire
Quote:
Quote:
Quote:
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