Old telephone conversion

[markymark2406]

I have just purchased an old BT phone which has been converted to use on the a modern BT system, on test the phone rings out fine but when you ring the phone it dosnt ring but picking the receiver up it connects ok. On further investigation the conversation has been done but the 3.3kohm resister wasn't in between connections 4and5 I have reinstated this but no joy
I have metered out the 4 wires on the cable and they are ok and also checked the resistance of the bell coils and they are ok

help please?

 

[sparkymarka]

have you tried it in the master socket or a slave ? Most modern phones don't need the capacitor in the master socket to ring , old phones will need this !

 

[markymark2406]

What capacitor? The phone line I tested it on is a BT infinity line

 

[bernardgreen]

The capacitor ( either in the phone or the master socket ) is essential for the bel to ring.

The speech and dialling operates on a DC supply ( 50 volts when the phone is on hook and about 9 volts when off hook ).

The bells operate on a AC supply. The DC is prevented from reaching the bell by the capacitor. The AC to ring the bell does flow throug the capacitor to reach and operate the bell

As said most modern phone have a capacitor in them and can work with 2 wires from the master socket to slave socket, old phones do not have the capacitor and they need the third wire to connect their bell to the capacitor in the master socket.

http://www.britishtelephones.com/howtele.htm is a good source of telephone knowledge

 

[Gerrydelasel]

On further investigation the conversation has been done but the 3.3kohm resister wasn't in between connections 4and5 I have reinstated this but no joy

The 3k3 resistor should only be used if the ringer coils are low impedance (about 500 ohms each). If they have '2k' printed on them then you should not use the 3k3 resistor or it may not ring properly / at all.

Check that the armature can move easily (WD40 on the bearing if necessary) and check the gaps for iron filings -these can stop the bell ringing. (Blow them out with an air can).