GPO 746 bell tinkle problem

[royalbox]

I'm in the UK and am currently testing 2 GPO 746 telephones that I've been restoring. I have them on 2 extensions. One of the phones (I'll call it the green one for clarity) has bell tinkle when you dial on the other (ivory one). If I dial on the ivory phone the green one doesn't tinkle, even if I swap them over on the extensions.

Here's the confusing thing: I checked the master socket and extensions and none had the bell wire connected. I then remembered that I had broadband problems a couple of years ago and it was suggested on the forum of my ISP to disconnect the bell wire.

I thought these old phones required the bell wire to ring, but they ring without it. They are wired internally as described in all the conversion guides I've read: white and blue wires from the line cable going to the bell ringer.

I've now connected the bell wires in the master and extensions but still get the bell tinkle. However, I'm really confused how they rang without the bell wire connected at all. Can anyone throw any light on this for me?
Barry.

[andre_janew]

I don't know anything about GPO telephones, but if this were a WE500 I would say that the bias spring needed adjusting.  Reversing the polarity of your ringer might also solve the bell tinkle problem.

[Jack Ryan]

How are the phones wired? Both pre P&S (N846) or both P&S (N8846) or one of each?

Pre P&S phones will work on P&S (connected to a master socket or extension socket) but both with tinkle just as they did on pre P&S wiring.

You should not have P&S phones connected to P&S wiring with the bell wire disconnected as the bell wire is also part of the audio circuit.

If you have P&S wiring with the bell wire disconnected and P&S wired telephones, the bells won't ring or tinkle. As one phone rings, at least that one must be wired pre P&S. Where exactly is the bell wire disconnected? If it is disconnected at the master socket but otherwise in place, it might be that a P&S wired phone is getting ring via the other phone.

Sorry, I don't have enough of a handle on the wiring to make proper sense of the problem.

ADSL is probably not happy with P&S wiring and there will probably be a splitter at the master socket to separate ADSL and telephone circuits.

There are no bias springs on UK telephones (and many others). Hasn't been since about 1900.

Jack

[dsk]

  I'm sure we may solve this together.

For everyone, it is some minor differences between US and most European vintage phones. The European phones does pretty often not have any anti tinkle device at all, no bias spring, and no PTC.

The UK system solved the problem differently from most other counties, the made a master socket where they did put in a 1.8-2 microfarad capacitor, from here they splitted up the system with a common third wire to all ringers.

As Barry told us, in his system the third wire is abandoned in hence of not disturbing the data transmission, so we actually have returned to US looking system, with only 2 wires. (And please leave it that way)

Barry; connecting the 3rd wire will not have any effect, since your phones are connected as 2 wire phones wit separate capacitors.
It may be one issue, if the 2 slave sockets has a third wire connection, one of the phones may work as master for the other if they not are configured 100% the right way.  The best way to test this out is to leave the bell-wire disconnected in the master socket, and call in with only one phone connected at the time, if one rings, but not the other, we have another issue.

Back to the tinkle. One of the easiest way to go around this is to use a spring from a pen and apply as little tension as possible to let the ringer rest in one position, and if needed increase the tension until the tinkle is gone, but it still rings. 

A more fancy way to do it is to install the circuit described here http://www.epanorama.net/circuits/tele_privacy.html in the bell wire.

Actually this circuit in the main socket will make the UK system work with 3 wires, and without disturbing the data transfer. (I have just tried out the triac solution, and also by using a quadrac)

dsk

[Jack Ryan]

Barry; connecting the 3rd wire will not have any effect, since your phones are connected as 2 wire phones wit separate capacitors.

We don't know that Dsk, the phones, or one of them, may be wired for P&S. I asked that and other questions in my previous post but have not yet received an answer.

Regards
Jack

[royalbox]

Thanks for the replies, I posted late last night so couldn't reply any sooner (sleep and all that).

I'm new at this phone lark so don't know the term P&S.

I think I should take a step back and learn a bit more about how the wiring of these phones works. It obviously isn't how I thought.

Anyway, I've hopefully attached a diagram of the way the phones are both wired and a photo of the PCB where I've crudely overlaid the circuit tracing to see what goes where.

If the blue bell wire that goes to T6 wasn't connected to the capacitor in the master socket after all, I assume that the bell rang because the white wire going to T19 (via T18) goes through the hook-switch and then to T6 (according to the PCB tracings) and then to the bell. Is that right?

EDIT: Tested with my meter, with hook-switch down, no connection between T18/T19 and T5/T6. If blue wasn't connected to master socket, I don't know how the bell rang.
END EDIT

I think I'd better see if I've understood so far before going further! Thanks very much everyone for your help.

Barry.

[Owain]

P&S is Plug and Socket.

Try removing the strap T9-T8.

Official diagram is here
http://www.samhallas.co.uk/repository/n_diagrams/5000/N8846.pdf

[royalbox]

P&S is Plug and Socket.

Try removing the strap T9-T8.

Official diagram is here
http://www.samhallas.co.uk/repository/n_diagrams/5000/N8846.pdf

Plug and socket, thanks. T9 goes to the C1 the other side of which goes to T7 where nothing is connected, so I didn't have that link anyway. Thanks though.


I'll put this problem on hold then until I can work out what made my phone ring with one bell wire disconnected. Makes no sense to me. I'll check all the extensions and see if there is a wiring problem.

Thanks all.

[royalbox]

Okay, I've worked out what was going on with the bell wire. Maybe it's different here in the UK and maybe I need to update, but I have each phone plugged into an ADSL filter to filter out broadband. I removed all the filters and plugged the phones directly in the socket and did a ringback test. Neither the 746 nor the modern phone rang. I plugged the modern phone into the filter again, redid the test and it rang but not the 746. I plugged the 746 into its filter again, repeated the test and they both rang.

Please correct me if I'm wrong but I conclude that each filter has a capacitor like the master socket that connects one of the line wires with the bell wire which is why the 746 rings even without the bell wire connected in the master socket.

I'd really like to rewire the extensions and separate the broadband at the master socket and do away with the individual filters so I'll look into that in the new year.

Sorry for this confusing thread that went off into a tangent, but at least I found something out that I wouldn't have realized had I not posted it! I'll deal with the tinkle problem later.

Thanks all

[Jack Ryan]

Please correct me if I'm wrong but I conclude that each filter has a capacitor like the master socket that connects one of the line wires with the bell wire which is why the 746 rings even without the bell wire connected in the master socket.

I believe that is correct - UK filters contain a (telephone) capacitor; I don't know of any others that do. The presence of that capacitor is what made me think that one of the phones was wired pre P&S (plug and socket) so the second phone rang via the capacitor in the first. Anyway - that sorts that out.

I think you should decide if you are going to use P&S wiring or the old (pre P&S) wiring. I would use the old form but that's just me.

Where is your ADSL modem relative to your master socket? If it is close, I would use a master splitter and then the phone wiring is isolated from the ADSL wiring and no filter is needed at each phone.

If you use P&S wiring, you won't have trouble with bell tinkle.

If you use old wiring, you will get bell tinkle (using parallel connected telephones). The "conversion resistor", the 3k3 or perhaps 4k7 Ohm resistor, may be enough to damp the tinkle. If not, get some Thermistors 1A off eBay - they will definitely stop it. You could use a Bellset 41 as well but the thermistor is slightly smaller and less obtrusive.

Regards
Jack

[royalbox]

Thanks Jack. I've converted the phones to plug and socket, think I'd like to keep them that way.

My ADSL modem/router is as far away from the master socket as it could be unfortunately. Upstairs at the other end of the house.

After watching a youtube video on the subject, I wondered whether I should get an ADSL Faceplate Splitter for the NTE5 master socket and run the broadband signal on a separate pair of wires to the extensions. The extensions are connected via 3 pair wiring so have wires to spare. I could then do away with the telephone filters and reconnect the bell wire at the master and maybe get improved broadband. I'll have to look into it.

Thanks again,
Barry.

[Jack Ryan]

Barry,

>> ADSL Faceplate Splitter for the NTE5 master socket

That's the sort of thing I was calling a master splitter. Good move, just unfortunate that the modem is so far away and you have to share a cable.

I assume that you are using wired Ethernet connections and not just wireless.

Regards
Jack

[twocvbloke]

I'd recommend getting the proper Openreach-branded Mk.3 VDSL faceplate for the master socket, for one it works fine with ADSL, and the other is it includes a ring capacitor in the faceplate, negating the need for the filters, and thirdly, you can run a "data extension" off the inside of the faceplate so you can route your modem to somewhere else using twisted pair cable (such as Ethernet cables)...

And just to clarify things a bit with terminology, here in the UK, it's not called "P&S", its PSTN, Plug and Socket Telephone Networking...

The cause of the bell tinkle though is usually caused by leaving the capacitor inside the phone connected in the ring circuit, though if yours has been disconnected properly, then the other thing could be the gongs just need rotating ever so slightly further away from the clapper, so the clapper can't hit the gong as easily without ringing current being applied...

The other solution, a thermistor No. 1A-1 in series with the ringer, and if you can find one of those, you're doing better than me!! 

[royalbox]

Thanks both of you, that's very helpful.

Jack, Yes, I am using wired and not wireless.

The capacitor in the phone is definately not in the ring circuit (assuming it's the 1.8uF C1/C2), the incoming wires go straight to the bell ringer. Perhaps it's the capacitors in the filters that's causing the problem, so I'll get the faceplate you mentioned and update the cabling as discussed and take it from there.

Actually , I've been wanting to move the extension sockets to more convenient spots but don't want to get the carpet and floorboards up! Maybe one day.

Thanks again,
Barry.

[dsk]

Barry, I guess you are right in your conclusions. If you use an extra pair to the modem, and have one splitter, or you keep on using filters on each jack is will make a difference for the tinkle, but I do not know how it will affect the data speed.  (When I had oldfashioned dial up modem, the speed went up when I disconnected the phones (or actually the ringers) the speed went up.  When i did put in the quadratic the problem was solved.)
The filters with capacitors will kind of transfer the phone back to the old system, and the tinkle problem must be solved by installing a mechanical spring, an NTC resistor or a another solution like the privacy circuit mentioned earlier.   The privacy circuit will give you the bonus of not being able to listen to the other phone when it is in use.

dsk