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Old 26th Sep 2023, 10:01 pm   #1
zcacogp
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Default GPO746 not ringing

Hi,

First post, please forgive any lack of awareness.

I have a GPO746 telephone which I have used on a regular BT telephone line before. It rang and would dial out fine, and you could talk on it; the only thing it wouldn't do was allow you to navigate called menus ('Dial 1 for Customer service, dial 2 for sales' etc). I appreciate that this is because it is a pulse dialling device and such menus are tone-activated.

We've now moved house and telephones are run through a Virgin HomeHub. I'd like to make my old GPO746 work on this. I've plugged it in using the provided RJ11-BTJack connector and some of it works; it won't ring and it won't dial out but you can answer calls on it and both speak and listen.

The problem with it not dialling out is again presumably due to it being pulse and not tone. I can live with this. However I would like it to ring.

A bit of research on this forum suggests that the problem is a lack of a ringing capacitor, and I've discovered that it does ring if you plug a broadband filter in line with the 'phone. Presumably such a filter provides a capacitor on a third terminal in the phone. Would it therefore be possible to take the relevant capacitor out of the broadband filter and connect it within the 'phone?

I've taken the top off the 'phone and this is what it looks like (attached file). Those connections seem to be as follows;

White - T18
Green - T15
Blue - T5
Red - T8

The following terminals are bridged:

T4 - T5 - T6 (T4 - T5 is a small wire but it is there).
T8 - T9
T16 - T17 - T18 - T19

C2 also seems to be missing (probably never present).

This seems all to be in line with what other people have described on here with the exception of the Green wire on T15, which many people don't have connected.

So my question is whether there is any internal re-wiring I can do to make the 'phone ring or whether I can simply bridge a capacitor across a couple of terminals to make it ring? And, if so, can I pinch a capacitor from the broadband filter to achieve this?

Thanks in advance for your help.
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Old 27th Sep 2023, 12:11 am   #2
Graham G3ZVT
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Default Re: GPO746 not ringing

The problem is with "The provided RJ11-BTJack connector", modern phones don't require the ringing signal on pin 3 of the BT connector, so they don't bother with the capacitor.

If you replace it with one like this
https://www.ebay.co.uk/itm/262671846092
it will work.

Personally I would just stick with the ADSL microfilter.

You can rewire the phone so it uses its existing internal capacitor, but as you need an adapter anyway to RJ11, it can kill two birds.
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Last edited by Graham G3ZVT; 27th Sep 2023 at 12:19 am.
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Old 27th Sep 2023, 8:04 am   #3
dagskarlsen
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Default Re: GPO746 not ringing

A pulse-tone adapter like Dialgizmo may solve the dialing problem. A capacitor in the phone may solve the ringing problem, if you are lucky, the capacitor is in there so you do just have to move some straps.

Try to put in the straps as in this diagram: https://www.vintage-radio.net/forum/...2&d=1405435789
From this tread: https://www.vintage-radio.net/forum/...d.php?t=107719
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Old 27th Sep 2023, 12:35 pm   #4
wd40addict
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Default Re: GPO746 not ringing

Don't know which Virgin hub you have, but my 746 works fine with the Superhub 3. A capacitor made it ring and pulse dialing just works - I suspect the latter is hub dependent.
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Old 28th Sep 2023, 11:24 pm   #5
Oldcodger
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Default Re: GPO746 not ringing

Quote:
Originally Posted by zcacogp View Post
Hi,

First post, please forgive any lack of awareness.
I can live with this. However I would like it to ring.
Firstly, welcome. I can understand your problems as I was a GPO apprentice in the latev60s with this beast.
First, theres a site giving ful circuit diagrams of the 746 etc. Sam Hallas N diagrams( the GPO techs BIBLE TO phones. http://www.samhallas.co.uk/repositor...ms/popular.htm.
N diagrams were the diagrams associated with GPO phones. For some reason, each phone diagram ( for the phone had 100 added to the phone number. e.g. a 706, was N diagram N806 AND 746 WAS n846. If you look at site http://www.samhallas.co.uk/repositor.../0000/N846.pdf, you will see the information for a 746 PHONE .
iVE ADDED ( FROM MEMORY OF OVER 50 YEARS AGO) what I remember rrom the days at GPO TRAINING.
Hopelfully it might show you how phones were connected then and now.
Difference is that in old days, speech was in parallel, with bells in series. Today, in an alalogue system, speech is in parallel, as are bells.
To achieve this bell circuits need the resistance increased in todays world.
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Old 29th Sep 2023, 10:58 am   #6
Pellseinydd
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Default Re: GPO746 not ringing

Quote:
Originally Posted by Oldcodger View Post
Quote:
Originally Posted by zcacogp View Post
Hi,

First post, please forgive any lack of awareness.
I can live with this. However I would like it to ring.
Firstly, welcome. I can understand your problems as I was a GPO apprentice in the latev60s with this beast.
First, theres a site giving ful circuit diagrams of the 746 etc. Sam Hallas N diagrams( the GPO techs BIBLE TO phones. http://www.samhallas.co.uk/repositor...ms/popular.htm.
N diagrams were the diagrams associated with GPO phones. For some reason, each phone diagram ( for the phone had 100 added to the phone number. e.g. a 706, was N diagram N806 AND 746 WAS n846. If you look at site http://www.samhallas.co.uk/repositor.../0000/N846.pdf, you will see the information for a 746 PHONE .
iVE ADDED ( FROM MEMORY OF OVER 50 YEARS AGO) what I remember rrom the days at GPO TRAINING.
Hopelfully it might show you how phones were connected then and now.
Difference is that in old days, speech was in parallel, with bells in series. Today, in an alalogue system, speech is in parallel, as are bells.
To achieve this bell circuits need the resistance increased in todays world.
The plug in version of the Telephone 746 was the Telephone 8746 see N8746 The website hasn't got all the GPO telephone diagrams. I have over 80 volume os the smaller earlier N diagrams going back to the original ones of 1917. For instance Sam Hallas's website has N935 as being the N935 cordless table top PMBX. I've got an original N935 for a wall mounted 1+4 plug and cord PMBX. I have a another shelf full of the later A5/A4 N diagrams. I've also ket the different editions of each of all the N diagrams. I've also got originals of the 1909, 1899 and the 1886 sets of GPO telehone diagrams. First started collecting in 1960 when GO were having a clearout of a basement and there was a large box of very early N diagrams being dumped. I asked if I could have them and was told 'help yourself'. Been there for many years untouched. With N diagrams you were instructed to destroy early copies when a new version was issued - hence early ones were rare. I have original N diagrams which relate to particular subscribers on the original Lorimer type automatic exchange at Hereford.

The website britishtelephones.com has far more information on GPO and other UK manufactured telephones and has details on converting them to plug & socket working including converting a Tele 746 to become a Tele 8746


I was a GPO Technical Officer 60 years ago ! How time flies - doesn't seem that long ago since we wound the handle to call the excange then again to 'ring off' at the end of the call. My oldest exhanges are some National Telephone Co magneto cord switchboards. My automatic GPO exchange is now coming up to 100 years old! Still got my old phones connect to CNet, our relica of the GPO public network as it was in the 1960/70's. London is still 01 xxx xxxx on our network! Free to connect to and all the calls are free - worldwide. Even BT have lines off our network! PM me for details.

Ian J
CNet 0352 2979#
MR ETD 053-6278
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Old 30th Sep 2023, 11:45 pm   #7
Oldcodger
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Default Re: GPO746 not ringing

Pellseinydd- like you- TO on Transmission Mtce. I remember the old lady on an island in my younger days ( possibly Eigg) telling me &mentor( Maintenance TO) that a sub could not be contacted and that a ring on the handle( magneto exchange) got no response. Simple answer= wire down. My first Transmission place was OB/b- hidden in the bowels of a Scottish hillside in the days of the cold war. Time flies from my days surfacing between the islands of the inner Scottish highlands, where I met blokes like Tex Geddes ( who told me He could have been my dad) and other worties .
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Old 10th Oct 2023, 6:25 am   #8
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Smile Re: GPO746 not ringing

I'm embarrassed to say that as an ex GPO engineer and Virgin Media (business, not cable TV) I don't understand this.
Isn't a VM hub a cable modem and therefore any phone that connected to it should be ip?
I've been retired for 7 years but at the time I left, business POTS lines (and residential) were delivered on copper from muxes in street cabinets.
I might understand better if I ever used the product but I didn't live on the franchise. My sister does and her set-up is a CM and copper telephone line.
Please enlighten me!
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Old 10th Oct 2023, 1:39 pm   #9
Graham G3ZVT
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Default Re: GPO746 not ringing

Quote:
Originally Posted by Test Desk View Post
I'm embarrassed to say that as an ex GPO engineer and Virgin Media (business, not cable TV) I don't understand this.
Isn't a VM hub a cable modem and therefore any phone that connected to it should be ip?
I've been retired for 7 years but at the time I left, business POTS lines (and residential) were delivered on copper from muxes in street cabinets.
I might understand better if I ever used the product but I didn't live on the franchise. My sister does and her set-up is a CM and copper telephone line.
Please enlighten me!

As you imply, a true IP phone would just plug into a LAN socket on the router (or connect by WiFi), like anything else.

The router in this case has a built in ATA (Analogue Telephone Adapter) so the customer can keep their existing POTS phones, and, if implemented correctly, they won't even notice the difference after the loss of their copper pair. (Until the power goes off anyway)
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