GPO 332L wiring question

[Voxophone]

Hi,

This is probably a very basic question but it's one I can’t seem to find a solid answer to. I have a GPO 332L telephone which I’d like to get working on a modern telephone socket. This will be the first time I’ve attempted this and I’m unsure about some of the wiring involved.

According to this page (http://www.britishtelephones.com/pstconv1.htm) I will need to connect red, white, blue and green cores of the new cable to the phone. These seem to refer to the older colour code system, so I’ve looked up the modern equivalents.

Red and green seem to correspond to Line A and Line B in modern terms, however blue and white seem to correspond to the modern ‘green’ pair which is not used in the socket. If my interpretation is correct there will be no connection to the orange bell wire at the socket. Is this correct? If so, why do the blue and white cores need to be connected at all (except for neatness)?

Thanks

Liam

[Dave Moll]

In the red/blue/green/white scheme the assignments are as follows:
red = B leg
blue = ringer
green = spare (or earth for an earth recall PBX)
white = A leg

For yellow/green/red/black:
yellow = B
green = ringer
red = spare
black = A

If your cable has something different from above, I would probably pass.

[TonyDuell]

Unless you have a need for the anti-tinkle facility (which I never thought was that important!), I find it easier not to mess about with the wiring inside these old telephones but rather :

The 300 series has 3 terminals associated with the old line cord. The a-wire (Terminal 1), the b-wire (terminal 9), and the extension bell (terminal 2). If there are no extension bells, terminal 1 is strapped to terminal 2, either inside the telephone or inside the block terminal.

Disconnect this strap and replace it with a 3k3 resistor to increase the bell impedance. Connect the white wire of the new line cord to terminal 1, the red wire to terminal 9. Insulate the other 2 wires of the new line cord. You can even keep the old line cord and block terminal and connect the new cord to the block terminal.

Diagram N432 applies.

[Voxophone]

Originally Posted by Dave Moll

If your cable has something different from above, I would probably pass.

So does this mean that the white/colour striped wiring system (seen here: http://www.wppltd.demon.co.uk/WPP/Wi...ext_wiring.gif) is used for wiring sockets only, rather than the actual cords to the telephones?

[Dave Moll]

Yes, the "fixed" wiring uses the thick/thin combinations blue/white & white/blue for the first pair (B leg and A leg respectively) and orange/white & white/orange for the second pair (ringer/spare). This is just the start of a much larger scheme for multipair cables in which the primary colours are blue, orange, green, brown and slate (grey), and the secondary ones are white, red, black, yellow, violet and pink - to give 30 possible pairs of colours.

As TonyDuell says, you can use just the first pair (white/blue to white and blue/white to red) if you're not worried about loop disconnect (pulsed) dialling causing "bell tinkle" on other 'phones connected in parallel.

[Oldcodger]

in short -yes. The wiring shown ,between sockets ,is solid . This is shown as four wires, but typical telephone cable is either six wire or eight wire, with four sets of colours, each white with a colour marker and colour with a white marker.
six = Blue/orange/green.For eight add brown.
Wiring from the socket to the telephone ( Never call it a 'phone) ,for the older 200/300 series uses an older cloth covered cable with the inners coloured as before. I'd imagine that this sort of cable is available with a BT plug attached, but if you are not bothered about it, replacement cables for modern telephones are available with a BT plug on one end and a clip in socket at the other, with four conductors. Sometimes the conductors are as per colour code ,sometimes not. It's easy to snip off the Telephone end socket, but the wires are stranded, and I'd say difficult to connect to the 300type terminals, unless you can find some method of fitting a terminal to them, bearing in mind that they may have braiding inside. I have managed ( at times with difficulty) to fit these to IDC terminals. But ,you are only interested in finding which of the colours in any cord goes to --
Terminal 2 -A leg of line
Terminal 5- B leg of line
Terminal 3- ring return.
Have a look at https://www.google.co.uk/search?q=bt...3pnOfEZthwM%3A

for a better understanding.
For the purists- they wire a house etc for several extension phones on one line ( known as plan 1) , as per the relevant N diagram. As long as all sockets carry the same colour to terminals 2/3/5, then all is well . Personally ( and I'll get flamed ,no doubt for this ) ,I always wire colours high. ( e.g. Blue with white marker goes to terminal 3).
Someone mentions this colour code giving rise to 30 pairs. Forget that, first there's a set of primary colours from Blue to slate, all with a marker. then there's another set of markers from WHITE/ RED/ BLACK AND YELLOW. That's 20 pairs. Repeat that with coloured tape markers on the outer - another four /five and that gives a cable of 100 pairs. Add bands to each 100 pairs , and ad infinitum.

[Voxophone]

Thanks everyone for clearing this up. I've now had the telephone working for both incoming calls and dialling out. In fact its having to earn its keep already as I accidentally snipped the cable to our modern device...

I do have another 332L which has been given the same treatment, however this is unable to dial out at the moment as the dial mechanism is running slow. I've confirmed that this is the problem by speeding up the dial with my finger, which does allow calls to be made. I have some clock oil on order and will try giving it a good clean. Hopefully this will do the trick.

[David Garside]

Good afternoon all.
I have a 332L, with I think a similar problem as above, but before I delve too far, could I ask a bit of advice please.
I bought the phone about 19 years ago and had it working for about 5 years when we put it away in storage. It is wired with the modern plug etc.
On digging it out, I find that there is no dial tone, although I get a momentary tone as the dial is returning. It will ring when the phone is picked up, but there is a pulsing sound in time with the ringing.
I'm wondering if it needs a new conversion ki, has the BT system been changed in the time it's been out of operation?
I've checked with a multimeter that the switch hooks are disconnecting etc, and the continuity of the handset wires. The dial returns in the standard time, and can't find any broken wires etc. There's no resistor (3.3k) on the block connector, which makes me think it needs a new conversion kit.
Would someone be able to point me in the right direction please.
Thanking you.

[giraffenigel]

Have you changed service providers in the meantime? It sounds to me like the symptoms you get when the phone provider doesn't support pulse dialling.

[Dave Moll]

I am puzzled by DG's stated symptom that there is no dial tone except for a momentary burst while the dial returns. I would have blamed this on incorrect wiring that only enables a loop with the dial off-normal (i.e. moved from its rest position) had it not been for the assertion that it had previously been working. Is there any chance of an image of how the 'phone is wired, especially the wiring of the dial.

As to the lack of a 3K3 resistor, this is not relevant to your current problem. The only purpose of this is to reduce the load on the line (REN) caused by the 1K bells, as they might prevent other ringers from receiving enough current during ringing.

[David Garside]

Hello all.
Thank you for your replies.
Yes, I have changed provider, to Vodafone, last October, so that may be the problem, I never thought of that!
I've checked the wiring to the dial and the colours are as follows... back of dial... screws at the bottom... left to right... Red, Pink, Brown, Grey and Blue. I will try to post a few pictures over the weekend when I finish work.
I only mentioned the resistor as it may be that the original conversion may now be out of date, and need updating.
I've found and downloaded a wiring diagram so will double check against that.
Thank you again for your help. Much appreciated.

[giraffenigel]

Could you take the telephone to a friends house, preferably with BT as their provider, and try it there?

[David Garside]

Hello again.
My daughter has a BT line, so will try it there the next time I visit. A good suggestion, one I should have thought of myself!
I've taken a few photo's of the wiring, how do I add them please? Thank you.

PS. I've added the photo's to my album. Thank you.

[AC/HL]

This sticky explains the process: https://www.vintage-radio.net/forum/...ad.php?t=77650

[dagskarlsen]

Originally Posted by David Garside

On digging it out, I find that there is no dial tone, although I get a momentary tone as the dial is returning. It will ring when the phone is picked up, but there is a pulsing sound in time with the ringing.
I'm wondering if it needs a new conversion ki, has the BT system been changed in the time it's been out of operation?
I've checked with a multimeter that the switch hooks are disconnecting etc, and the continuity of the handset wires. The dial returns in the standard time, and can't find any broken wires etc. There's no resistor (3.3k) on the block connector, which makes me think it needs a new conversion kit.

As Dave, I am conserned about the short sound of dial tone.
This may be a sign of error in the transmitter circuit. A strap between T4 and T5 will short out the transmitter, but give you dial tone (if I am right).

If I am right the searching will be limited to the part of the circuit between these 2 terminals.

Testing at a BT line will just test if the rotary dial servise works or not.

dsk

[David Garside]

Aha, thank you. I've just tried shorting 4 and 5 together, and yes I now have a dialling tone. I didn't try dialling etc, so I take it, I need a new transmitter, microphone. Many thanks for that.

[TonyDuell]

I assume that's terminals 4 and 5 on the main terminal block inside the telephone, not the 5 way one on top of the chassis that links to the dial.

If so, then the transmitter is the most likely suspect, but it could also be a broken wire in the handset cable. Remove the transmitter from the handset. To do this, you'll see a little hole in the side of the mouthpiece pointing towards the earpiece end of the handset. Push a suitable rod in there to release the catch and turn the mouthpiece anti-clockwise to undo the bayonet fixing. Lift of the mouthpiece and then the transmitter unit.

In the cavity that the transmitter came out of you'll see pin in the center at the botton of the cavity and a curved spring contact at one side at the top of the cavity. These are the 2 connections to the transmitter. Try connecting a clip lead between them, which would have the same effect as shorting terminals 4 and 5 if the cable is good. Try the telephone again, do you still get dialtone?

Also try measuring the resistance (with a normal ohmmeter) between the centre socket on the end of the 'top hat' on the transmitter and the metal case of the transmitter (transmitter out of the handset). I would expect a few hunded ohms. If it is very high or open, the transmitter is defective.

It might, of course just be bad contacts between the transmitter connections and the connections in the handset. If the transmitter checks out, and shorting the contacts with a clip lead gets you a dialtone, then try cleaning the contacts.

[David Garside]

Just checked the transmitter and it's one circuit. There's continuity between the handset contacts and the connector block on the chassis, so the wires are good. The transmitter rattles when I shake it....granules inside I suppose. Can you suggest a place where I can buy a replacement please? I think I remember reading on here that a later one can be adapted to fit.
Thank you for your help everyone.

[Dave Moll]

Yes, the electret transmitter 21A (red-cased version) can be inserted by removing the outer casing, connecting the white incoming handset wire to one terminal and a wire between the other terminal and the common terminal in the handset - with the central spigot (which may need to be removed) for the carbon transmitter and the red handset wire.

Make sure the transmitter is held in a position where it can't touch the handset terminals. This may need some padding if the spigot is removed.

Alternatively, if you're more concerned with keeping it original than with speech quality, I may have a spare working carbon granule transmitter you can have. An electret transmitter should, however, guarantee good speech output.

[dagskarlsen]

Nice to hear you located whats wrong. I have several versions of this bakelite housing, used in Norway, and Sweden, and one of them has a circuit witch like yours do not give dial tone without the transmitter. By some reason European transmitter capsules from thet time, makes more noise than North American transmitters.

Putting a resistor of 220 ohms (1/2 W) across the carbon transmitter reduces the noise considerably, and the other party does not complain about weak signal.

Sometimes the old carbon transmitters comes back to life (but not good as new) by rolling them on an uneven surface so the carbon is well shaked.

dsk