A.T.E. No. 6 Telephone

See also the A.T.E. Model L11750A

Telephone No. 6 adjustments

A.T.E. No. 6 Telephone
Engineering Bulletin 525 (Issue 2)
Date 02/60

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.

Figure 1

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 cover.

Figure 2

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.

Figure 3


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.

Figure 4

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.

Figure 6

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.

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 designs.

Figure 7

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 electrode.

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 granules.

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.

Figure 8

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 follows:-

  • 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 transmitting impulses.

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 ringer are:-

  • 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.

Figure 9

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 alternative.

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.

Figure 10

Line-Termination Block
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.

Figure 11


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.

Type 6A
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 only.

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).

Figure 12

Figure 13

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 required.

The P.A.B.X. Instruments
Type 6P81

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.

Figure 14

Figure 15

Type 6PB2
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.

Figure 16

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 required.

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.


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Last revised: May 05, 2023