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Old 5th Oct 2019, 2:51 pm   #1
Ken Taylor
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Default 706 telephone conversion

I have decided to sell off some of my collection of cherished instruments including some 700 series phones. I have modified them as per instructions found in this forum, but cannot get any to ring. I know the "bell" wire was disconnected at the master socket to improve ADSL performance some years ago so it's now just the two wires, so can anyone direct me to the correct links to make in the 706 and 746 types?
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Old 5th Oct 2019, 3:21 pm   #2
ThePillenwerfer
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Default Re: 706 telephone conversion

If you're selling them as leave them as they are as they are 'correct.'

If you want to use one yourself on two wires see attached. You'll only need to change one.
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Old 5th Oct 2019, 4:01 pm   #3
TonyDuell
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Default Re: 706 telephone conversion

What I do for 2-wire 706s and 746s is wire them exactly as in the appropriate N diagram (N806, N846) including the original line cord. I terminate that in a Block Terminal 52 (the original junction box) and fit a 3k3 resistor in place of the strap for the extension bell there (which puts that resistor in series with the 1k bell in the telephone). Then wire the 2 line wires to the appropriate terminals in the Block Terminal.

That is, wire as the N diagram, connect a 3k3 resistor between the white and green wires of the line cord and connect the line wires to the white and red wires of the line cord.

This has the advantage that the telephone is absolutely 'as original' inside.
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Old 5th Oct 2019, 9:14 pm   #4
OscarFoxtrot
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Default Re: 706 telephone conversion

Quote:
Originally Posted by Ken Taylor View Post
I have decided to sell off some of my collection of cherished instruments including some 700 series phones. I have modified them as per instructions found in this forum, but cannot get any to ring. I know the "bell" wire was disconnected at the master socket to improve ADSL performance some years ago so it's now just the two wires, so can anyone direct me to the correct links to make in the 706 and 746 types?
The easiest way is to plug them in for testing via a broadband microfilter. These usually contain a ringing capacitor to recreate the bell wire.
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Old 7th Oct 2019, 2:36 pm   #5
Ken Taylor
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Default Re: 706 telephone conversion

Thanyou for the good advice. Since my original posting I have plugged some of my phones (the ones with BT plugs) into the Master Socket and they ring, but not in extensions. I'll try the broadband filter idea.

Now, our phone service is delivered by Virgin Media fibre and there is
something I have always wondered, how does a fibre system produce ringing current? There is no mains connection that I can see indoors so it must come along the coax from the green box outside.
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Old 7th Oct 2019, 8:09 pm   #6
ThePillenwerfer
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Default Re: 706 telephone conversion

Virgin actually run two cables: a COPPER co-ax one for broadband and TV and a twisted-pair for telephone. Their talk about fibre is simply marketing bull as that only goes to the street cabinet and it's copper from there to your house.

I believe that they are changing how they do things on new installations but this is how mine was that was installed five years ago and every other that I've actually set eyes on.
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Old 7th Oct 2019, 8:33 pm   #7
AndiiT
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Default Re: 706 telephone conversion

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Originally Posted by Ken Taylor View Post
... how does a fibre system produce ringing current?...
It doesn't, as has already been mentioned Virgin Media's legacy services are what is known as a HFC network (look it up on Wikepedia) the fibre trunk is long haul into an area and after that the conversion to copper is done at one of the larger street cabinets which then feeds a number of smaller cabinets that have individual copper "drop" cables to the customer premise, originally this was done using Siamese cable which had coax for the broadband and tv services and twisted pair copper for the telephone.

Virgin have now introduced "fibre to home" where the fibre is fed from the street cabinet to the outside of the customer premise, the conversion to copper being done at the external termination box - this means that the telephone service has to be provided via the broadband hub using VOIP principles - from the 29th March this year all new telephone installations have been provided via the broadband service and there are plans to eventually migrate existing customers over to "voice over glass" this will take a number of years though.

So even a fibre to home service is still HFC once it is inside the customer premise.
It will be some time before the fibre trunk goes direct in to the broadband hub and it will still be the circuitry in the hub which provides ringing current and power for speech.

Regards

Andrew
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Old 13th Oct 2019, 5:46 pm   #8
Ken Taylor
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Default Re: 706 telephone conversion

Thank you for the explanation, I can see further research is needed as I just like to know the technologies behind every connection to my house! There is a small cabinet just outside and they brought a coax cable (RG59) from there through the wall, which was split off to slightly better looking cable to the TV and router.

Cheers
Ken
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