Produced in the early 1980's these telephones were used in pairs and sold as an intercom system to the general public.  They in a box, with an instruction leaflet in the colours red or grey.  They were produced in the BT Factory at Cwmcarn, in Wales.

Operation is by lifting the handset on one of the phones and turning the dial.  The buzzer at the distant telephone will operate until the dial returns to rest.

Under the handset on the master telephone is a battery holder, but a 9 volt power adaptor could be plugged into a socket on the rear of the telephone if batteries were not to be used.

Connected together using a 4-wire cable (30 metres supplied).

Signalling the other telephone was achieved by turning the dial which sounded a buzzer on the distant telephone.  The dial off-normal springs are used for this purpose.

The bells are not used because the voltage is 9 volts DC, so the ringer mechanism was removed.  The bells are left in situ to support the dial.

Telephone wiring

These phones are not wired as standard and in fact each one is slightly different to the other.  Generally on the circuit board model is used.

The original dial would have been cut off at the PCB and new wires provide, connecting only the brown, slate (grey) and blue leads.

The dial also has the insulator bush removed on the off normal spring tip.

The regulator has been removed and replaced by linking the B, C and D PCB U sockets to T3 - this are soldered connections.

Extra wire links are provided:-

  • Between T8 and T10.

  • Between T9 and T16 (main only).

  • Between T13 and T19.

  • Between T6 and T11.

Strap links are as follows:-

  • Between T8 and T9.

  • Between T18 and T19.

The battery holder is only on the main phone is is connected to:-
Red wire - T18
Black wire - T4
1k ohm resister between T4 and T16.

The line cord is connected to:-
Red wire - T18
White wire - T8
Green wire - T4 (main)
Green wire - T15 (secondary)
Blue wire - T6

The buzzer is connected to:-
Orange wire - T12
Black wire - T4 (main)
Black wire - T15 (secondary)

The dial is connected to:-

  • D1 - Blue - T12
  • D3 - Grey - T11
  • D4 - Brown - T13

The two telephones are connected together with the cords colour for colour.

Many thanks to Peter McIntyre for his assistance.

Wiring Diagrams

Master telephone


Secondary Telephone

Both telephones connected




Boxed and sold as an intercom system


The battery holder (main only) can be seen between the switchooks.
To the right of the handset cord is a power adaptor connector (used instead of batteries)



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Last revised: November 16, 2021