Can an old (1962) telephone be connected to a modern BT socket?

Hello. as header really. Phone is an old bakelite gadget with 3 wires that would have been hardwired into a junction box. Can this be connected to a more modern plug in BT socket and if so ~ how?

Many thanks Nick.

Reply to
Nick
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Reply to
Dave Plowman (News)

Of course it can.

The whole exchange kit is backwards compatible to the year dot, except pre loop disconnect dial stuff won't off-hook get you an operator to ask to connect you...But you can dial by tapping the off-hook switch..;-)

I cannot remember which wires go where though: there will be two signal and one bell wire..so if you can identify which plug wires to connect to in the first place..two will have about 50V DC across them, so that's one way to find them....the bell wire will give you a nasty tingle when someone rings you, so conncect theh hamster across various pairs and dial in from yer mobile. When he leaps, that's teh bell wire.. there are only a finite number of combinations to try, and you won't screw the exchange up. Not sure about the hamster tho..

Try em till it works..

Reply to
The Natural Philosopher

Problem with older phones is the bells are low impedance with effectively a REN of several and will likely stop any others in the house ringing. But there are ways round this.

Reply to
Dave Plowman (News)

BUT EVERYONE ON UK.TELECOM.BRODBAND SWERARS BLIND MODERN PHONES DON'T USE THE BELL WIRE ANYWAY...

Reply to
The Natural Philosopher

Some modern phones use the bell wire, some modern phones don't. Besides, that is not relevant to the REN. Most modern electronic phones are high impedance and don't load the phone line with low impedance bells and electromagnetic earpieces. The ring detection is done electronically, maybe across the pair, maybe from the ring line, either way, it has very little effect on the rest of the circuit.

Reply to
Paul Herber

In article , Nick writes

Yes. I'm assuming it's not so old that it doesn't have the BT standard terminal layout - two rows of screw terminals, 1 to 9 on the top row and

10 to 19 on the bottom row.

Get yourself a BT plug-to-spade-connector lead (aka "a line cord"). Ebay item 170186909828 for example.

Open the phone and remove existing cord.

Remove strap between terminals 4 and 5 and insert a 2.2kohm 1/4W resistor. This is to reduce the current drawn by the bell - the bells in old phones are low impedance. You may see "500" on the bell coils - this is their impedance (500+500). Ensure there is a strap between terminals 5 and 6 and connect the BLUE wire from the cord to terminal 6.

Ensure there is a strap between terminals 8 and 9 and connect the RED wire from the cord to terminal 8.

Ensure terminals 16, 17, 18 and 19 are all linked with straps and connect the WHITE wire from the cord to terminal 18.

Connect the GREEN wire of the cord (it's unused) to terminal 14.

Test.

Be warned that old phones like this may degrade data calls using a modem or affect a broadband connection.

Be aware that the DC voltage on a phone line is 48V, and that the ringing current is ~90V AC. Don't work on a phone that's plugged in, as the ringing voltage can be hair-raising.

Reply to
Mike Tomlinson

Some do, some don't.

Reply to
Dave Plowman (News)

Or the incoming pair...

Reply to
Dave Liquorice

Especially if you are stripping it with your teeth at the time. Telex lines were even worse (up to 160V peak AC when ringing).

Reply to
Andrew Gabriel

Not if it's a bakelite one - these have a different terminal layout. The connections varied depending on the type of phone, ie normal, shared service or whatever.

Is there a type number printed on the base of the phone, such as 332,

312, or similar?
Reply to
Frank Erskine

So? I thought this thread was about *old* telephones - which *do* use the bell wire when connected to a modular socket - and even when hardwired if they were not the first in line.

ISTR that old bells had an impediance of 1k ohms - thus having a REN of 4 - whereas later ones with a REN of 1 had an impedance of 4k ohms. So, basically, you need to wire a 3k ohm (some say 2.2k - not quite sure why) resistor in series with the bell, and you're sorted.

Reply to
Roger Mills

It took me a while to work out why I was getting belts from a BT block I was attaching lines to for an OB. It was issing with rain, I was soaked and standing in a puddle. All the lines where controls, 4 wires or musics ie no volts. I then remembered that we also hada DEL...

Didn't think telex lines rang as such but the data is +/- 80v from a hi-z source. I don't think I've been daft enough to come into contact with the fed to the magnet on my Creed 444 (or any of te other mechanical telex machines I've had in the past).

Reply to
Dave Liquorice

Some had two coils, which could be wired in series for 4K and parallel for

1K.

The old extension system wired the bells in series and required the coils in parallel. the newer plug (modern type sockets) have the bells in parallel, and require the coils in series.

Reply to
<me9

I can't remember the old connection colours, but just cut a lead with plug off a modern but redundant phone. There is a web site dedicated to the UK phone system which carries lots of information about connecting old phones to the modern system. Impulse (loop disconnect?) dialing is still supported by the UK exchanges, so there is no reason for it not to work.

Reply to
Harry Bloomfield

In message , Roger Mills writes

2.2k being a preferred value of a power series perhaps
Reply to
geoff

The public network never had the 500 ohm bell coils in parallel in the phone - they were always wired in series. Very occasionally private circuits had the coils in parallel. As you say though, in the old system the bells were connected in series, up to (officially!) a maximum of four. Or was it six; and four for a party line? The early 'plan 4' system of plug and socket telephones was a bit of fun. There had to be at least one fixed bell (usually a separate bellset was permanently connected) and each socket had to have a break jack to maintain continuity of the bell circuit when a phone was plugged/unplugged.

The concept of REN didn't exist until the new system came about.

Reply to
Frank Erskine

It hurts!

I can't feel a normal 50v telephone line voltage, unless there's some back emf putting nasties on the line. Telephone ringing voltage is a bit uncomfortable though.

Reply to
Frank Erskine

It was 4 for the longest line length supported.

Back in the days of BT approvals in Baynard House, I took a couple of devices along to get their approvals, which was a remarkably unscientific process.

For the REN number rating, they supply a line simulating the longest line length, and a (704?) standard phone on the end. The phone is ringing. You plug in your appliance. If the phone stops ringing, you get a REN of 4, and if it carries on ringing, you get a REN of 3. If you have bought a second sample of your appliance, you are invited to plug that in too. If the phone carries on ringing, you now get a REN of 1.5. If you have bought a third sample of your appliance, you can now try connecting that. If the phone carries on ringing, you now get a REN of 1. You can carry on going if you have even more samples with you. When I was at GEC, it was rare for us to have more than one sample available to take along for testing, so most of our stuff got a REN rating of 3, even though it was probably much lower. If you look around at phones with REN ratings, you'll find they are normally

1, 1.5, or 3, and this explains why (e.g. there was no way to get a REN rating of 2). The first caller display units I saw had a REN rating of 0.25, for which they must have taken 12 of them along for testing (although testing had been taken over by BABT by then, and they might have changed the procedure).
Reply to
Andrew Gabriel

Probably not. You should have seen what they did with an X.25 gateway that I took to them at one point.

Reply to
Andy Hall

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