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Old 4th Sep 2021, 6:44 pm   #1
GreasedMonkey
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Default Old telephone, impulse buy, not working.

Hi all, a bit of a change from my usual lurking place of the old TV section.

So me and offspring1 found ourselves with a bit of free time today, so wondered across to the museum over the road that houses, amongst other things, a collection of old telephone kiosks, and some exchanges. I got chatting to one of the volunteers who looks after the exchanges and he informed me they had some old phones for sale to try to raise funds. So I handed over 10 of my finest pounds and came away with the beauty in the pictures. I assume it is either a 746 or 1307 as these two numbers are stamped on the base.

It had been fitted with a modern lead with plug on the end, but I was told it “probably would not work as had not been properly updated”. I could have chosen a different set which had been updated and he said definitely would work, but this was twice the price and I like a challenge.

On returning home, I plugged it into the master socket and it does not work. It will ring when I ring the number, but does not dial out (our exchange does support LD dialing) and there is not dial tone on lifting the receiver, only very front clicks can be heard.

Can anybody point me to a source of information that will help me wire the thing correctly. I have (hopefully) attached a photo of the wiring as it stands, oddly most of the wires coming from the dial assemble are not connected, is this normal?

Thanks.
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Old 4th Sep 2021, 7:01 pm   #2
Dave Moll
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Default Re: Old telephone, impulse buy, not working.

The red line cord wire needs to go to T8 rather than T9 (which is one end of the internal capacitor (see diagram N846 for details).

You also need the blue wire to T6 and to remove the strap between T6 and T7.

Depending on what else is connected to the line, you may also need to replace the strap between T4 and T5 with a 3.3K resistor, but that's a later refinement once the 'phone is working.

The green wire is not used and should be parked on a spare terminal, such as the one previously holding the blue wire.
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Old 4th Sep 2021, 7:08 pm   #3
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Default Re: Old telephone, impulse buy, not working.

It's a 746. You'll find full details of the required wiring on this page:

https://www.britishtelephones.com/pstconv1.htm

Alan
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Old 4th Sep 2021, 7:41 pm   #4
GreasedMonkey
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Default Re: Old telephone, impulse buy, not working.

Thanks both.

Following the links and having a bit of a read, I now have it wired correctly (I think, proof is in the testing I guess).

However, I do not have any 3K3 resistors in stock. How accurate does this value need to be?
I have 2K7 and 3K9 in stock, or if this is not close enough can make something up with 2 or more in series. Is it better to be low, high, or should I make it spot on?

Thanks again.
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Old 4th Sep 2021, 8:03 pm   #5
Dave Moll
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Default Re: Old telephone, impulse buy, not working.

I don't think the value is too critical. If 3.9K drops the voltage too much for the bell to ring properly, use the 2.7K.

As I say, though, it will work with the strap rather than a resistor. The resistor is simply to prevent this from hogging too much of the ringing current for any parallel telephones to ring properly.
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Old 4th Sep 2021, 8:04 pm   #6
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Default Re: Old telephone, impulse buy, not working.

Either will probably be fine. I've successfully used 2k7 in the past.

Alan
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Old 4th Sep 2021, 8:36 pm   #7
G6Tanuki
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Default Re: Old telephone, impulse buy, not working.

For testing, plug it direct into the BT master-socket, _not_ via an ADSL microfilter.

Not all microfilters pass the 'ring capacitor line' feed through to their phone-sockets. Most phones for the last 40-odd years have been 2-wire and don't need the third-wire ring-capacitor-feed so many ADSL microfilters don't provide it.
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Old 4th Sep 2021, 9:09 pm   #8
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Default Re: Old telephone, impulse buy, not working.

Thanks all.

The phone is now fully functional.
We use VDSL internet so no filters to worry about.

I opted for the 3K9 resistor, purely because it was the first of the two packets I picked up. I think it may be a little on the high side as it has resulted in what I would describe as a ‘soft and gentle’ ring. But I think I am going to leave it as it is loud enough and I quite like it a little subdued.

It is now in bits again as I have the plastic bits soaking in a mild soap solution to remove the 50 or so years of dirt.
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Old 4th Sep 2021, 9:16 pm   #9
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Default Re: Old telephone, impulse buy, not working.

Next job is to try and recreate the paper disc for the centre of the dial.
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Old 4th Sep 2021, 10:11 pm   #10
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Default Re: Old telephone, impulse buy, not working.

Here's a quick way of generating a label in keeping with the period:

http://going-digital.github.io/telephone-dial/

Alan
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Old 5th Sep 2021, 6:24 am   #11
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Default Re: Old telephone, impulse buy, not working.

You might want to get the appropriate N diagrams from Sam Hallas's site. These are essentially the circuit diagrams for the telephone

N846 covers the original Telephone 746. N8846 covers the official plug-in version with a 4k Ohm bell. The 746 has a 1k bell, adding the series resistor (which was never 'official' on this telephone although it was on some others) effectively increases the resistance.
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Old 5th Sep 2021, 1:17 pm   #12
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Default Re: Old telephone, impulse buy, not working.

Quote:
Originally Posted by ajgriff View Post
It's a 746. You'll find full details of the required wiring on this page:

https://www.britishtelephones.com/pstconv1.htm

Alan
it is indeed a 746. The appropriate diagram ( sampas N diagrams ) is N846.
http://www.samhallas.co.uk/repositor.../0000/N846.pdf
ETA- for the beginner, GPO added 100 to the diagram number for the phone. So a tele 746 will use diagram N846 /a Tele 706b will use N806 and a 332 will use N432.
Hopefully that will be of some use to someone. I can't remember why. Most possibly lost in the transition from Plans( 1/1a/5 etc) to how 60 circuits gets fed down a submarine cable or how 960 get shoved from town to town on a coax cable .

Last edited by Oldcodger; 5th Sep 2021 at 1:25 pm.
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Old 6th Sep 2021, 9:31 am   #13
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Default Re: Old telephone, impulse buy, not working.

Thanks Alan. Little disc made and installed.

All back together again now and nice and clean.

Thank you all for the help.
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Old 6th Sep 2021, 11:25 am   #14
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Default Re: Old telephone, impulse buy, not working.

Quote:
Originally Posted by ajgriff View Post
It's a 746. You'll find full details of the required wiring on this page:

https://www.britishtelephones.com/pstconv1.htm

Alan
That is a most interesting link - amazing how many phones are around and full marks to whoever took the time to compile that.
I have a General Telphones unit in the shack which dates from the 80's -it was left over from a project. They were in Osnaburgh St.
An excellent phone with particularly good receive audio - something which benefits my ancient hearing!
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Old 6th Sep 2021, 5:35 pm   #15
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Default Re: Old telephone, impulse buy, not working.

Quote:
Originally Posted by lesmw0sec View Post
That is a most interesting link - amazing how many phones are around and full marks to whoever took the time to compile that.
I believe that Bob Freshwater first launched britishtelephones.com in 1998. It's an absolute mine of high quality information and has been my go to telephone resource for many years now.

Alan
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Old 6th Sep 2021, 6:45 pm   #16
Dave Moll
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Default Re: Old telephone, impulse buy, not working.

I would go along with that. Between Bob's site and the N diagrams on Sam Hallas' site they are invaluable.
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