P 1104


1. General
A call-point may take the form of a street pillar or a police kiosk. In a street call-point party line there are three stations, the first (or A) station and the second (or B) station being termed side stations.  The third (or last) station on the line is known as the terminal station.  Each party line is capable of serving a maximum of three call-points with full selective signalling.  Up to two additional side-stations may be provided, if required, except on party lines which are teed at an exchange or cross connexion cabinet for signalling reasons (TRANSM., Tele., B 3571 and B 3572).  They must be connected as additional A and B stations in the manner indicated in Fig. 2 of P 3103.  An additional side-station is signalled at the same time as the normal side-station and incoming calls to the switchboard are displayed on the same lamp as the normal side-station.

2. Sub-station call-points

These call-points are generally situated in private residences or other premises in which the public have not access to the telephone.  Since the probability of two sub-stations being required as two side-stations on one party-line group is remote, only two types of unit are available, i.e. for “A” and “terminal“ call-points.  If necessary, however, a “Unit, Telephone, P.A. No. 8A" can he converted to work as a “B“ point by fitting the B-point cam which is supplied with and carried in the case of, the “Unit, Telephone, P.A. No. 8A" (see P 3103).


3. Telephones
A specially-designed telephone “Unit, Telephone, PA. No. 6A, 6B or 6T,” (see pictures below) is installed at these points, from which dual telephone facilities are provided, i.e.:-

  1. By loudspeaker and transmitter available to the public upon simply holding open a door, which is self-closing but non-locking.
  2. By means of a microtelephone available only to the police, or other authorized persons in possession of a key.

    Unit, Telephone, PA. No. 6T - Engineering side Unit, Telephone, PA. No. 6A - Public side
    The loudspeaker has a microphone mounted centrally

4. Public call door
The loudspeaker and transmitter, for public use, are located behind a protective grille, and do not require handling by the caller.  The base of the loudspeaker cone is fixed in a metal ring, which fits closely against the back of the protecting grille, and the transmitter is fixed inside the cone.  It is only necessary for the public to pull and hold the door open, and thereafter to speak in a normal manner in the direction of the grille.  The answering voice of the police operator can be clearly heard, as a valve amplifier at the police station is used in this circuit and speech from the operator to the public call-point is amplified, normal speech from the public call-point being received by the operator.

5. Public call door pin

An adjustable projecting pin is fitted on the inside of the public call door.  When the door is closed, this pin projects through an aperture in the grille and presses a plunger, which keeps a pulse mechanism in a wound position.  The act of opening the public call door releases the pulse mechanism (see par. 11).

6. Public call door-closing spring

The door, when released at the termination of a call, is made to close slowly by the action of a check-action door-closing spring.

7. Telephone No. l64

This is provided for police use and is suspended on a gravity-switch.

8. Mounting for Unit, Telephone, P.A. No. 1
This mounting base, which is held in position by three screws, is provided for mounting the telephone unit and for the permanent connexions at pillars and police kiosks. Mounted upon it are the fuses and a double-pole switch for the local power supply for lighting the signal lamp.  When used in pillars, this switch is kept in the operated position, whilst the maintenance door is closed, by means of an adjustable projecting pin on the inside of the maintenance door, and is released when the door is open.  The object of this arrangement is to cut off the power supply whenever the door is opened. In kiosks, the switch is held in the operated position by the cover of the “Bracket, P.A. No, 1.

The line wires, the earth wire to the instrument, and also the power leads, are terminated on a special 5-point jack mounted on the base, and these connexions on the telephone unit are similarly connected to a 5-point plug.  Two guide rails are provided on the mounting base so that the plug on the telephone unit can be jacked-in to the connexions on the base, the telephone unit being kept in position by means of two screws.

10. Bracket, P.A. No. 1
When used in pillars, the mounting base is fitted direct on the pillar head. The public call door and the protecting grille form part of the pillar head, and the telephone unit, when jacked in on the mounting base, fits close to the protecting grille.  When the apparatus is fitted in a police kiosk, however, a “Bracket, P.A. No. 1" is necessary.  This consists of the public call door, grille structure and the support for the “Mounting for Unit, Telephone, PA. No. 1“ as one unit, and is provided with a removable cover.  The whole assembly is fixed in a suitably-constructed aperture in the police kiosk by means of metal corner crosspieces, bolted into bosses provided on the back of the grille structure.

11. Pulse mechanisms

The pulse mechanisms consist of two modified automatic dial mechanisms with metal covers.  One of the mechanisms is operated by the opening of the public call door, and the other by the removal of the police microphone from the gravity-switch.  The mechanisms are normally held in the wound position, and, when either of the mechanisms is released, a train of earth pulses is connected, via the pulsing springs, to the B-wire of the line for signalling the switchboard.  The number of pulses transmitted varies with the different call-points, to provide selective signalling.  A second set of springs completes the line circuit, and on the public call mechanism a third set of springs is necessary to complete the transmitter circuit.

12. A mercury-tube contact, fitted over the pulse mechanism of the public call door, is mechanically operated when the door is opened, and causes the lamp on top of the pillar or, in the case of kiosks, both external and internal lamps, to glow steadily while the public door is open.

13. Signalling relays

The signalling relays in “A” and ‘B“ units are of the AC. type and are provided with heavy-duty tungsten contacts.  These relays respond to ringing current, and cause the signal light to flash by alternately completing and disconnecting the circuit of power supply to the lamp at one-second intervals.  The signalling relays in terminal units have similar contacts hut are of the polarized type and respond to battery reversals.


14. Units, Telephone, P.A. Nos. 8A and 8T
These telephones are provided with “Telephones No. 164”.  The “A” unit is supplied with a B-point cam for conversion to B-point working; arrangements should be made for this conversion to be made locally, when necessary.  The equipment is assembled in a wooden box for wall fixing.

Units, Telephone, P.A. Nos. 8A Units, Telephone, P.A. Nos. 8T
Units, Telephone, P.A. Nos. 8A
Case open
Units, Telephone, P.A. Nos. 8T
Case open

15. Pulse mechanisms
The pulse mechanisms are similar to those fitted to the “Unit, Telephone. PA. No. 6” and are described in par. 11.

16. Signalling relays
The signalling relays in “A” and “terminal“ units are of the A.C. and polarized types, respectively.  The operation of each type of relay is similar to that described in par. 13.

17. Alarm bells

Magneto bells are provided on “A” units and trembler bells on “terminal“ units.  The operating circuit in each case being completed by tile associated signalling relay.  Extension-bell facilities can he provided.

BACK Home page BT/GPO Telephones Search the Site Glossary of Telecom Terminology Quick Find All Telephone Systems

Last revised: February 23, 2021