GPO 8746 Telephone Bell - UK Vintage Radio Repair and Restoration Discussion Forum

newton26 · 2nd Apr 2020, 3:02 pm

Hi,

I've just bought a GPO 8746 telephone. Its a nice looking old thing and seems to be mostly working fine.

Only issue is when I dial in the bell doesn't ring. If I pick up the receiver when dialling in it does answer.

I opened the case and found a loose blue wire from the coil(?). I'm guessing this is my problem.

Where should it be connected to?

AC/HL · 2nd Apr 2020, 4:04 pm

T4 or T16, whichever is not connected: http://www.thechipmunk.net/phones/8746e.htm

TonyDuell · 2nd Apr 2020, 4:13 pm

The bell coils say 500 Ohms on them (on each of them), making this a 1k bell. That means that the telephone is probably not an 8746 (which normally has a 4k bell, 2 off 2000 ohm coils) but a 746 that has been converted to the new wiring.

The workaround is to put 3300ohm (3.3kOhm, 3k3) resistor in series with the bell coils. The easiest way to do that is to remove the metal strap (link) between terminals T4 and T5, then connect the resistor between those. As Bill says the wires from the bell coils go to T4 and T16 (T16 is strapped to T17, T18 and T19).

Diagrams N846 and N8846 apply to the Telephone 746 and Telephone 8746, you can get them from Sam Hallas's website.

russell_w_b · 2nd Apr 2020, 4:26 pm

Quote:

Originally Posted by TonyDuell

'That means that the telephone is probably not an 8746 (which normally has a 4k bell, 2 off 2000 ohm coils) but a 746 that has been converted to the new wiring.'

It could still be an 8746. The 8746 meant the instrument was configured to be used on the BT plug and socket system. I have an 8746 with 500 Ohm bell-coils.

If it was an 8746C, however, then yes: it would have the 2K bell coils fitted. Or so I was told when I asked exactly the same question about my 8746!

TonyDuell · 2nd Apr 2020, 5:05 pm

That is why I said 'probably not an 8746'. The common 8746 has a 4K bell, it's what you generally need for domestic installations. The older 746 (hardwired, not plug-in) has a 1k bell.

I've seen reference to the 1k bell 8746 in diagram N8846, but where was it used?

russell_w_b · 2nd Apr 2020, 6:23 pm

Quote:

Originally Posted by TonyDuell

I've seen reference to the 1k bell 8746 in diagram N8846, but where was it used?

I think that's a clue, Tony. Mine was used as an extension on a small PABX, as far as I can tell from the dial label. It's coming back to me now... This particular telephone was rescued from a skip after a clear-out in some business premises in Cockermouth.

Think that would be the main difference: DEL would have a 4k ringer; PABX extension a 1K one.

ThePillenwerfer · 2nd Apr 2020, 7:09 pm

To simply answer the OP's question:—

A photo showing the entire circuit board would help but it looks like the loose wire should be connected to one of the three screw terminals joined together. Undo one and put the loose wire under it. Odds are it will then work in practise whatever the theory says.

ThePillenwerfer · 2nd Apr 2020, 7:58 pm

I couldn't add this diagram earlier as I wasn't at my main computer. Don't worry about the resistor at this stage. If it works with the strap in place and all your other 'phones still ring there's no need to bother.

newton26 · 2nd Apr 2020, 8:20 pm

Quote:

Originally Posted by ThePillenwerfer

I couldn't add this diagram earlier as I wasn't at my main computer. Don't worry about the resistor at this stage. If it works with the strap in place and all your other 'phones still ring there's no need to bother.

Thanks very much, the diagram was a big help. All working now.

I only have the one landline phone (this one now) so I don't think I'll need the resister. I checked my broadband speed before and after and it was exactly the same so I am assuming its all good?

ThePillenwerfer · 2nd Apr 2020, 9:50 pm

Sounds like it.

Glad it helped.

2nd Apr 2020, 3:02 pm	#1
newton26 Diode Join Date: Apr 2020 Location: Coventry, Warwickshire, UK. Posts: 6	GPO 8746 Telephone Bell Hi, I've just bought a GPO 8746 telephone. Its a nice looking old thing and seems to be mostly working fine. Only issue is when I dial in the bell doesn't ring. If I pick up the receiver when dialling in it does answer. I opened the case and found a loose blue wire from the coil(?). I'm guessing this is my problem. Where should it be connected to? Attached Thumbnails

2nd Apr 2020, 4:04 pm	#2
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: GPO 8746 Telephone Bell T4 or T16, whichever is not connected: http://www.thechipmunk.net/phones/8746e.htm

2nd Apr 2020, 4:13 pm	#3
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: GPO 8746 Telephone Bell The bell coils say 500 Ohms on them (on each of them), making this a 1k bell. That means that the telephone is probably not an 8746 (which normally has a 4k bell, 2 off 2000 ohm coils) but a 746 that has been converted to the new wiring. The workaround is to put 3300ohm (3.3kOhm, 3k3) resistor in series with the bell coils. The easiest way to do that is to remove the metal strap (link) between terminals T4 and T5, then connect the resistor between those. As Bill says the wires from the bell coils go to T4 and T16 (T16 is strapped to T17, T18 and T19). Diagrams N846 and N8846 apply to the Telephone 746 and Telephone 8746, you can get them from Sam Hallas's website.

2nd Apr 2020, 5:05 pm	#5
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: GPO 8746 Telephone Bell That is why I said 'probably not an 8746'. The common 8746 has a 4K bell, it's what you generally need for domestic installations. The older 746 (hardwired, not plug-in) has a 1k bell. I've seen reference to the 1k bell 8746 in diagram N8846, but where was it used?

2nd Apr 2020, 7:09 pm	#7
ThePillenwerfer Octode Join Date: Mar 2011 Location: Sheffield, South Yorkshire, UK. Posts: 1,453	Re: GPO 8746 Telephone Bell To simply answer the OP's question:— A photo showing the entire circuit board would help but it looks like the loose wire should be connected to one of the three screw terminals joined together. Undo one and put the loose wire under it. Odds are it will then work in practise whatever the theory says. __________________ "Experts are only good at one thing: explaining why something will not work!"

2nd Apr 2020, 7:58 pm	#8
ThePillenwerfer Octode Join Date: Mar 2011 Location: Sheffield, South Yorkshire, UK. Posts: 1,453	Re: GPO 8746 Telephone Bell I couldn't add this diagram earlier as I wasn't at my main computer. Don't worry about the resistor at this stage. If it works with the strap in place and all your other 'phones still ring there's no need to bother. Attached Thumbnails __________________ "Experts are only good at one thing: explaining why something will not work!"

2nd Apr 2020, 9:50 pm	#10
ThePillenwerfer Octode Join Date: Mar 2011 Location: Sheffield, South Yorkshire, UK. Posts: 1,453	Re: GPO 8746 Telephone Bell Sounds like it. Glad it helped. __________________ "Experts are only good at one thing: explaining why something will not work!"