Newbie with a CIT 1958 phone - UK Vintage Radio Repair and Restoration Discussion Forum

DannyBee · 21st Nov 2016, 1:40 am

Hi all,

New to the forum and have a phone question so I joined as I'd like to learn more about vintage electrics.

I purchase a French phone which I've worked out is a cit 1958 and shares many components with the more popular U43. I couldn't find a conversion guide for this model so I tried to connect it by just using the BT wires spliced to the French wires and with two of the four wires connected everything works including the ringer!

Is it safe to use the phone like this as I've read on the forum of people adding rectifiers , capacitors etc but I can make and receive calls fine without touching the phone itself.

Thanks for any help

dagskarlsen · 21st Nov 2016, 12:20 pm

It is safe, to do what you have done. Using only 2 wires and no modification of the phone may cause that not all phones on the line will ring, or if you put up to many phones the exchange will act like you are lifting the handset on first ring, and just put it back again.
If it works it is OK, at least until you connect to many phones on the line.

To do it "right" you need to modify so the ringer circuit is connected to a third wire, and you may have to add an extra resistor.

I am sure someone here will criticize me for this, but I would have left it as it is as long as it works.

dsk

TonyDuell · 21st Nov 2016, 2:16 pm

Two wire connection, using the outside contacts (2 and 5) of the BT plug 431A is 'safe'. In fact most modern landline telephones are wired like that, and it is often recommended to do this on telephones used on a line that also carries ADSL broadband as the ringer connection can 'bypass' the filter.

The main problem with it is that a mechanical bell might 'tinkle' when other phones on the line are doing pulse dialing. I have never understood why this was thought to be a major problem, certainly it wouldn't bother me.

The other thing is that the bell coil resistance in your telephone is (if it is the same as a U43) about 2k. This is a bit low, and may draw enough current that other telephones in parallel on the same line will not ring properly. A resistance of around 4k is right for an REN of 1, so try connecting a 2k2 resistor in series with the bell. If the wiring is the same as the U43, then terminals 10 and 11 will be strapped on the terminal board. Connect the resistor in place of that strap, and have the line wire connected to terminal 10.

DannyBee · 22nd Nov 2016, 9:51 am

Great thanks for the help ! I wouldn't know where to start with modifying the ringer so I'll leave it as it is for now and hopefully start to learn a bit by reading things on the forum.

21st Nov 2016, 1:40 am	#1
DannyBee Retired Dormant Member Join Date: Nov 2016 Location: Wakefield, West Yorkshire, UK. Posts: 2	Newbie with a CIT 1958 phone Hi all, New to the forum and have a phone question so I joined as I'd like to learn more about vintage electrics. I purchase a French phone which I've worked out is a cit 1958 and shares many components with the more popular U43. I couldn't find a conversion guide for this model so I tried to connect it by just using the BT wires spliced to the French wires and with two of the four wires connected everything works including the ringer! Is it safe to use the phone like this as I've read on the forum of people adding rectifiers , capacitors etc but I can make and receive calls fine without touching the phone itself. Thanks for any help

21st Nov 2016, 12:20 pm	#2
dagskarlsen Heptode Join Date: Jan 2008 Location: Hakadal, Norway Posts: 643	Re: Newbie with a phone It is safe, to do what you have done. Using only 2 wires and no modification of the phone may cause that not all phones on the line will ring, or if you put up to many phones the exchange will act like you are lifting the handset on first ring, and just put it back again. If it works it is OK, at least until you connect to many phones on the line. To do it "right" you need to modify so the ringer circuit is connected to a third wire, and you may have to add an extra resistor. I am sure someone here will criticize me for this, but I would have left it as it is as long as it works. dsk

21st Nov 2016, 2:16 pm	#3
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,225	Re: Newbie with a CIT 1958 phone Two wire connection, using the outside contacts (2 and 5) of the BT plug 431A is 'safe'. In fact most modern landline telephones are wired like that, and it is often recommended to do this on telephones used on a line that also carries ADSL broadband as the ringer connection can 'bypass' the filter. The main problem with it is that a mechanical bell might 'tinkle' when other phones on the line are doing pulse dialing. I have never understood why this was thought to be a major problem, certainly it wouldn't bother me. The other thing is that the bell coil resistance in your telephone is (if it is the same as a U43) about 2k. This is a bit low, and may draw enough current that other telephones in parallel on the same line will not ring properly. A resistance of around 4k is right for an REN of 1, so try connecting a 2k2 resistor in series with the bell. If the wiring is the same as the U43, then terminals 10 and 11 will be strapped on the terminal board. Connect the resistor in place of that strap, and have the line wire connected to terminal 10.

22nd Nov 2016, 9:51 am	#4
DannyBee Retired Dormant Member Join Date: Nov 2016 Location: Wakefield, West Yorkshire, UK. Posts: 2	Re: Newbie with a CIT 1958 phone Great thanks for the help ! I wouldn't know where to start with modifying the ringer so I'll leave it as it is for now and hopefully start to learn a bit by reading things on the forum.