|P.O. ENGINEERING DEPT.
POLICE TELEPHONE AND SIGNAL SYSTEM
SWITCHBOARDS, P.A. 150 AND 150 TD)
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
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).
STREET PILLAR AND POLICE KIOSK
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
- By loudspeaker and transmitter available to the public upon simply holding open a door,
which is self-closing but non-locking.
- By means of a microtelephone available only to the police, or other authorized persons
in possession of a key.
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
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,
9. 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
callpoints, 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
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.