See also the A.T.E. Model L11750A
Telephone No. 6
A.T.E. No. 6 Telephone
Engineering Bulletin 525 (Issue 2)
The telephone case and handset are of a completely new design that is modern in
conception, aesthetically pleasing and functionally efficient. As shown in
Figure 1 the design is similar to that of the new B.P.O. No.706 telephone which
carries the approval of the British Council of Industrial Design. A new dial -
the A.T.E. No.5 dial - and a new A.T.E. ringer are incorporated.
The case is a one-piece thermo-plastic moulding of polymethyl methacrylate,
marketed under the trade name of Diakon, and is designed to be quickly removable
from the rest of the instrument. It functions as a cover and is secured to the
mechanism by two captive screws accessibly located in the cradle recess. A
moulded projection is also provided inside the front edge of the case, this
projection hooks under a metal plate screwed to the base, thus giving rigidity
to the assembly. Removal of the cover leaves the mechanism, including the dial,
undisturbed. The lower edges of the case are arranged to seat over the flanged
base to provide insect proofing.
A rectangular aperture, located at the top of the case, is designed to
accommodate a pushbutton micro-switch or a lamb. If neither is required the
aperture is covered by a dummy moulding fixed to the case by a spring clip.
Provision is also made for the addition of two push-buttons at the front corners
of the angled surface of the cover. To simplify this addition, drill-centre
spots and locating projections are provided on the inside. The push-buttons
would be secured to the mechanism and remain in position upon removal of the
The base is a one-piece moulding of black high-impact polystyrene, fitted
with four push-in artificial-rubber feet. As shown in Figure 2 connection points
for the cords and the internal wiring are provided in the base by twenty-four
tapped hexagon inserts. These are inserted by a force fit after moulding.
Nineteen are at rear of the base and five below and to the left of the dial.
Attached to the base are brackets for mounting the capacitor, cradle switch,
dial and ringer. The general assembly of the components on the base is shown in
the Figure. Figure 3 is a rear view of the base illustrating the handset-cord
and instrument-cord connections.
CIRCUIT AND WIRING
The B.P.O. No.332 telephone circuit is employed. Graphs of the sending and
receiving performances of this circuit are shown in Figure 4. The values were
obtained by using a 50-volt Stone transmission bridge (200 + 200 ohm relay), the
circuit of which is illustrated in Figure 5.
The circuit of the basic instrument is shown in Figure 6. The arrangements
for dial interrupter-spring spark quenching (the 30-ohm non-inductive winding of
the induction coil plus the 2-microfarad capacitor) and for radio-interference
suppression (the 0.1 microfarad capacitor) are retained. The use of a 3-point
plug and socket for line connection is, however, an innovation and mechanical
details are described later in the bulletin. Alternatively, a standard
line-termination block can be provided.
The components are pre-wired on the assembly bench with p.v.c.-covered
conductors. The conductors are fitted with ring-type clenched tags for
connection to the appropriate terminals, thus permitting easy removal of
components by dispensing with the need for a soldering iron. The handset and
instrument cords are fitted with spade tags, this enables them to be removed
without releasing the ring tags of the internal wiring.
EXTENSION BELL FACILITY
To effect the addition of an extension bell, the connection between points 1
and 2 (Figure 6) in the 3-point socket is removed. The extension bell is then
connected between these points and the bell instrument located where required by
the telephone user.
Figure 7 shows the handset with the transmitter and receiver withdrawn. The
body of the handset is a one-piece moulding of Diakon, shaped to give a
comfortable grip. It is fitted with a moulded cord-housing insert, cemented in
position at the transmitter end. The ear cap and mouthpiece are of the screw-on
type with coarse threads for robustness and quick removal.
The shaped horn around the mouthpiece has been eliminated on the new handset.
In order to ensure optimum transmission performance the relative angles and
positions of the earpiece and mouthpiece, and the length of the handset have
been calculated from the data obtained from extensive tests. The transmitter
diaphragm is more nearly opposite the user's mouth than in previous handset
The transmitter is identical with the B.P.O. No.13 and incorporates two
screw connections. Resistance to the penetration of moisture is ensured by a
coating of tough enamel on the diaphragm and by the breathing hole in the rear
The granules, of hard, burnished carbon, totally cover the electrodes and
flow around them in such a way that the pressure of the granules on the
electrode surfaces is maintained whatever the position of the receiver.
The conical diaphragm is made of thin but rigid metal. The walls of the
granule chamber are enamelled to prevent any electrical contact with the
The B.P.O. No.1L receiver, as previously used in the No.162 handset, is
fitted. The receiver casing has been modified so that the receiver can now be
inserted into the new shape of the handset.
The permanent magnet is of Alnico. The pole pieces have U-shaped lugs screwed
to the case to clamp the permanent magnet and coil assembly in position. The
interior of the receiver is sprayed with cellulose lacquer and the diaphragm -
of 9 mils thick Stalloy - is varnished black on both sides.
The A.T.E. No.5 dial of basic new design is used. Figure 8 is a rear view of
the complete dial assembly. Figure 9 illustrates the dial mounting. Two plates
are attached to the rear of the dial base-plate. These plates are in turn
secured to the dial mounting bracket by two screws. Slotted fixing holes in the
plates enable easy removal of the dial from its mounting bracket.
The No.5 dial transmits 10 impulses per second, with the standard 2:1
break-to-make ratio. A two-pulse masked period occurs at the commencement of
each impulse train.
The design of the new dial provides exceptionable accessibility to the
mechanism. With the exception of the main spring the complete mechanism is
attached to the rear of the dial base-plate. An easily-removable transparent
cover, secured to the base plate by two screws, provides complete dust proofing
with ready visibility.
The most modern materials and latest methods of manufacture have been
employed in the production of the dial, the main features of which are as
Simplicity of design and robustness of construction.
Complete protection against ingress of dust.
Recessed holes in the finger plate as distinct from through holes.
Provision for the inter-train pause to be made before the pulse train,
so completely ensuring that the dial attains its governed speed before
The finger plate has chaplets (arrow heads) marked on the underside at each
finger hole. This arrangement prevents scratching of the characters by finger
nails, pencils or other implements that may be used to wind up the dial. The
chaplets point to the position of the numbers on the external number-ring. The
finger plate and number-ring are coloured to match the handset and consist of
transparent Diakon mouldings. The appropriate characters are coloured to
contrast with the main body of the finger plate and number-ring.
Polyurethane foam tape is fitted behind the dial, within the inner
circumference of the number-ring, to complete the dust proofing.
A more comprehensive description of the dial is given in Engineering Bulletin
2324 'A.T.E. Type No.5 Dial'.
A single-coil single-gong ringer of a new design is fitted. The illustration
(Figure 9) shows the ringer assembly and the position in which it is mounted on
the base. A bracket, secured to the telephone base, prevents the gong from
twisting around on its central fixing screw. The salient features of the new
The construction is simple and robust.
It is light and compact.
There is ease of adjustment. The gong is self-adjusting leaving only the
air gap to be adjusted.
Owing to its high-resistance winding (1 650 ohms), it absorbs less power
than previous designs.
Efficient sound emission through gauze-covered holes in the base plate,
the gauze preventing possible ingress of insects.
- A manually-operable, external changeover lever which extends to the
underside of the telephone base enables the ringer to be used as a bell or
buzzer as required.
One springset is normally fitted but provision is made for the mounting of
an additional springset, if required, on the opposite side of the centre line. A
wedge-type spring-set is used, employing nickel-silver springs with twin silver
contacts. The springset comprises a two-make combination (make upon removal of
the handset) as required by the 332 circuit.
The instrument-connection cord and handset cord are both p.v.c. sheathed,
coloured grebe grey. P.V.C. grommets are fitted at each end of these cords. An
extensible handset cord is normally fitted but a straight cord can be supplied
if required. The handset cord employs tinsel conductors; the instrument cord
uses stranded wires. Spade-type clenched tags are fitted to all cord conductors.
A 3-point plug and socket is the standard method of line termination in the
No.6 telephone although a line-termination block can be supplied as an
Connection Plug and Socket
The instrument connection cord is terminated in a new, flat 3-point plug. A
3-point socket, associated with the plug, is designed for wall mounting. This
arrangement enables the telephone user to 'plug in' the instrument at as many
alternative locations for which he may care to make provision. The plug and
socket mouldings are of high-impact polystyrene, coloured grebe grey. Figure 10
illustrates the plug and socket.
The line-termination block is a moulding of high-impact polystyrene, shaped
to blend with the design of the telephone. There are no moulded inserts; threads
for the terminals and
cover-fixing screw are provided by nuts pressed into holes. There is a cord
entry, with grommet, at one end of the block, and 'knock-outs' for additional
entries in the cover. The cable entry is provided by a knock-out. There are six
terminals normally linked in pairs to provide a 3-way bloc k. The
line-termination block is illustrated in Figure 11.
TYPE NUMBERS OF A.T.E. NO. 6 TELEPHONE
The A.T.E. No.6 telephone is available in the following type numbers:-
- Type 6A - The basic automatic instrument.
- Type 6SS - The shared-service instrument.
- Type 6CB - The p.m.b.x. instrument
- Type 6PB1 - The p.a.b.x. instruments.
- Type 6PB2 - The p.a.b.x. instruments.
This is the basic instrument (Figure 1) for automatic working as described
in the preceding pages.
Type 6SS - The Shared-Service Instrument
This instrument employs a B.P.O. shared-service adaptor that utilises the
aperture in the top of the case to locate the necessary calling push-button.
Figure 12 shows the circuit of the shared-service instrument. A 4-point plug and
socket replaces the basic 3-point plug and socket and, in the cradle-switch
springset, a set of changeover contacts is employed instead of the basic set of
make contacts. Additional components are a changeover micro-switch operated by
the push-button, a rectifier and a Thermistor.
Where two subscribers share the same exchange line, the A wire from the
telephone instrument of the first subscriber is connected to the B wire of the
telephone instrument of the second subscriber, and the B wire of the first to
the A wire of the second. Figure 13 illustrates the subscribers' instrument
connections to the exchange line.
When the first subscriber's calling button is operated, a calling earth is
extended to the exchange over one of the exchange wires. When the second
subscriber's calling button is operated, earth is extended over the other
exchange wire. This arrangement enables separate line circuits with individual
metering to be employed in the exchange. The rectifier associated with the
calling button prevents the incidence of a false impulse when the calling button
is released and at the same time makes the calling earth effective on one wire
The Thermistor is wired in series with the bell circuit to eliminate tinkling
on the subscriber's bell when the snaring subscriber is dialling. The necessary
arrangement of the telephone instrument connections for shared-service working
means that the subscribers' conversations are non-secretive.
The terminals to which the additional components are connected are indicated
in the circuit diagram (Figure 12).
Type 6CB - The P.M.B.X. Instrument
The p.m.b.x. instrument has no dial, the dial aperture in the case being
filled by a dummy moulding. This instrument can be fitted with push-buttons as
The P.A.B.X. Instruments
This instrument employs one earthing push-button for Enquiry (Call-Back),
Transfer, Operator Recall and Executive facilities. The push-button is located
to the left of the dial at the front surface of the cover. The Type 6PB1
instrument is illustrated in Figure 14, the circuit being shown in Figure 15.
A 4-point plug and socket is used for line termination.
This instrument incorporates the facilities of the Type 6PB1, and in
addition, it has a push-button located to the right of the dial on the front
surface of the cover. This pushbutton is used for special facilities as
required. The circuit is shown in Figure 16. A 4-point plug and socket is used
in conjunction with a 3-point plug and socket for terminating this instrument.
If a further push-button is required this can be located at the top of the
instrument case in the space otherwise occupied by the dummy moulding.
Variants of the above Types
When ordering variants of any of the above types of instrument, the nearest
type should be quoted together with particulars of the extra facilities
The dimensions of the No.6 telephone are:-
Base: 8-7/16 in. by 5-3/4 in. (21.5 cm by 14.6 cm)
Height (including handset in rest position):-
4-7/8 in. (12.4 cm)
Weight (including handset):-
3 lb 8oz (1.6 kg)
Length of handset:-
9-3/8 in. (23.8 cm)
Weight of handset:-
10-1/2 oz (300 g).
The following single-colour range is provided.
Black, ivory colour, light French grey, forest green, lacquer red, topaz
yellow and concord blue.
Duo-tone colours are provided in grey - light French grey case and elephant
grey handset, and green - aircraft grey-green case and forest green handset.
The dial and outer number-ring are coloured to match the handset.