Australian Post Office
Telephone No. 801

Automatic, Table telephone

Basic dial telephone.

801 (Dated 1965)

Note that the dial has fillets or chaplets (the arrows)
The British Post Office used chaplets on their Telephone No. 706
 

An article from the Telecommunications Journal of Australia
Dated February 1963

THE TYPE 801 TELEPHONE
By R. J. KOLE

INTRODUCTION
In January, 1963. a new type of Coloured telephone having a pleasing appearance and advanced technical features was made available to the Australian public. It was the fist type in the 800 Series to be released and iv known as the 801 type telephone. The telephone is designed for use in automatic exchange areas and incorporates automatic regulation at transmission performance. The general features of the design of the 801 telephone, together with its Circuit and transmission performance, are discussed in this article. In future issues of this Journal, the various components of the telephone will be dealt with in greater detail. Shortly after the candlestick telephone gave place to the moulded handset We. phone, designers realised that plastics offered the opportunity to make durable telephones in colours other than black Although coloured telephones were introduced into service its the Australian network during the 1930s, only the ivory instrument achieved any degree of popularity. Since World War It, a great many new plastic materials have become available commercially and many of these are very suitable for the manufacture of telephones in the full range of colours trout strong reds, greens and blues to pastel shades.

The Australian Office has been well aware of the need for a range of coloured telephones which would harmonise with colours used in modern interior decorating schemes. Accordingly, after calling tenders throughout the world, it was decided in September, 1961, to develop a new Australian coloured telephone as a joint project of Australian manufacturers, that is, Standard Telephones and Cables Ply. Ltd. (S.T.C.). and Amalgamated Wireless (A/sia) Ltd. (A.W.A.), and Australian Post Office engineers. For the first time the Post Office had control over all design features. Information about telephone design had been accumulated for the past IS years with a clew to the eventual design of an instrument for the Australian network and it is clear that the 801 type telephone is at least as far advanced as any other available at present on the world market.

The new telephone instrument is a development from the "Assistant" telephone designed by the Bell Telephone Manufacturing Co., Antwerp. Belgium. with which S.T.C. is associated. However, the design details, both external and internal, have been modified considerably to produce the Australian instrument.

GENERAL FEATURES
The objectives in the design of the new telephone were a high standard of performance throughout the service life, an aesthetically pleasing appearance, and economy, in both installation and maintenance consistent with the requirement for economic manufacture. Particular attention was given to the design of components to ensure that they could he manufactured to the quality level required to give a high probability of a long trouble-free service life. The unit construction principle is employed to simplify manufacture and maintenance. Individual components are grouped and arranged in sub-assemblies which are the fundamental units from which the complete telephone instrument is built.

The case and handset are moulded in a toughened polystyrene injection moulding material, Acrylonitrile Butadiene styrene (ABS). which combines light weight with high impact strength. The surface has good resistance to scuffing, marking, abrasion and scratching and is easily cleaned. Its addition, ABS resists aggressive chemicals such as acids, alkalis, and many solvents and is not adversely affected by substances normally used for household cleaning.

The five colours chosen for the first order of the new telephone are light ivory, mist grey, fern green, topaz yellow, and lacquer red. These are shown in the photograph on the front cover of this issue of the Journal.

The case functions primarily as a cover for the component assemblies and not as a mounting unit. It has therefore been possible to design it as a relatively thin, mechanically elastic shell with smooth contours. This case shape, together with the design of the gravity switch plungers, almost eliminates the danger of accidental operation of the gravity switch by the cords. The handset, when replaced, is directed into its correct position on the gravity switch plungers by a self-aligning action. It is nearly impossible to accidentally balance the handset on the telephone case in any position near the plungers without operating them. A built-in carrying handle in the form of a recess in the case is provided, which makes it easy to grasp the telephone and carry it in one hand.

With careful design of the layout, it has been possible to mount the induction coil, capacitors and gravity switch on a printed circuit card to form a compact printed circuit assembly. The "wiring" side of the printed circuit card is tropic-proofed after soldering. in order to prevent leakage currents between conductors due to "creepage" in moisture films on the card surface. The use of "quick connect" sleeves and studs allows easy and reliable connection of the component assemblies to cords and flexible links without the need for screw fastening or soldering. "Parking" studs for flexible links provide for possible variations of the basic circuit.

The handset is supplied In the same colour as the case. It is a shell moulding approximately half the weight of the previous standard handset. A convex transmitter cap without projections is provided, and the small mouthpiece horn on earlier handsets has been eliminated to improve the appearance without greatly affecting the efficiency of the instrument. The handset is slightly curved to bring the transmitter into the correct speaking position. Adaptor inserts in the handset cavities  allow the one of alternative types of receiver and transmitter capsules. An acoustic shock absorber "click suppressor" is mounted on the back of the receiver to protect the user from noises loud enough to cause discomfort.

The dial is adapted to the telephone case by use of a dial adaptor ring which also serves as an enlarged number ring. Placing the numbers away from the fingerplate reduces wear and obliteration of the numbers and makes identification more certain. By the substitution of alternative adaptor rings any modern dint can he accommodated. No letters or numerals are provided on the dial label and this allows adequate space for the subscriber's telephone number and the prefix of the national dialling code, when subscriber trunk dialling is introduced. Special numbering stamps are being developed so that the number can be printed on the label In a uniform manner by the installing technician. The dial mechanism and springsets are enclosed is a clear polystyrene dust cover. On the 811 telephone (the equivalent C.B. manual table telephone), a dummy dial is used to replace the dial and adaptor ring.

The bell has a single coil, polarised by a permanent magnet inside the coil, and wilt operate satisfactorily with ringing frequencies of 16 c/s to 50 c/s. A bell loudness control device, which can be operated by the subscriber to vary the loudness between a loud clear ring and a low level buzz, protrudes through the base plate of the telephone. To guard against the subscriber unintentionally placing himself out of call, the control does not silence the bell completely is the minimum position. The telephone base plate provides ventilation by pressed-eat louvres and is equipped with four rubber feet which have been designed to give the telephone a firm grip on the table surface.

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The handset cord is retractable, coiled, covered with P.V.C., and coloured to match the case mouldings. The cord was designed to have a retractile force much lower than the force required to make the telephone slip on all normal surfaces. The small pull created by the cord together with the light weight handset makes the telephone very comfortable to use. The cords are fitted with "quick connect' sleeves which plug on to the studs on the printed circuit assembly, the instrument plug and the transmitter inset. The cord pull is taken by grommets which are securely welded to the sheath instead of by strain cords. The conductors are also welded to the sheath at the ends to stop shear being drawn in when a strong pull tends to stretch the sheath. The instrument and handset cords, which enter the telephone through separate openings at the rear, can be interchanged without disconnection of the terminations, to cater for those instances where a telephone instrument in used mainly on the right-hand side of the table.

The connection between the instrument cord and the fixed wiring is made through a flat plug and socket unit which has been designed for minimum protrusion from the surface on which the socket is mounted. Provision is made for the plug to be made captive by changing one of the wood screws used to mount the socket. This is done by using a longer screw which passes through a tongue on the plug as well :is through the tease of the socket. Both long and short screws will be provided with each socket supplied. Plug pins and socket points provide for a maximum of six conductors from the telephone. Normally a three conductor cord is used. Provision is made for the connection of an extension bell by removing a strap in the socket. No alteration to telephone instrument, cord or plug is required. Contacts on socket springs 3 and 4 "make" when the plug is removed. This facilitates the standardisation of cable connections to instruments inn number working.

The electrical circuit provides the following improvements compared with circuits used previously:-

1. Transmitting, receiving, and side tone levels are automatically regulated within standard limits by using two voltage dependent resistors, more commonly known by the trade name "Varistors", as control devices.

2. The provision of a "click suppressor" across the receiver has made possible the sequencing of the gravity switch contacts to spark quench the contacts in the tine Circuit, to earlier circuits the gravity switch contacts had to be sequenced to short out the shock pulse which occurred when the gravity switch was operated; this contact sequence did not provide a spark quench.

3. The bell is disconnected from the line by the gravity switch while the handset is lifted.
   Provision is made for the addition of push buttons at the front corners of the angled surface of the case. These will be bought with the telephones or added in the workshops or in depots as required. Push buttons are secured to the base plate connected to the circuit assembly by flexible conductors fitted with "quick-connect" sleeves and remain in position when the case is removed.
   Ventilation of the interior of the instrument is provided by a ventilator grille at the rear of the case in the carrying recess. This, in conjunction with the fixed louvres to the base plate and the slots between the case and base plate, provides an adequate flow of air user the components to avoid condensation under humid conditions. It also allows sound-waves caused by the bull operation easy egress from the case.

CIRCUIT
The gravity switch contacts of the earlier 400 type circuit, which normally "made" when the handset was lifted to connect the bell circuit capacitor as a spark quench across the dial contacts, have been replaced by a changeover springset GS3, 4 and 5, so that the bell circuit is opened when the handset is lifted. This eliminates the high impedance shunt to speech current of a bell connected across the tine. The "break" side of either of the two changeover contacts provided on the gravity switch, may he used to disconnect external capacitors connected in parallel with telephone capacitor for ringing purposes. The capacity across the impulse springs can thus be controlled in these instances and the impulse distortion that occurs with excessive capacity avoided.

Circuit Diagram - CE11021

The gravity switch contacts previously in series with the "A" line, have been moved so that they are in series with the "B" line, This has two advantages:-

1. The "B" line potential is isolated on one side of the 1.5 microfarad capacitor and GS22 contact when the handset is cradled. This enables maximum separation of conductors of opposite polarity in the design of the printed circuit card layout.

2. On "hanging up" the gravity switch contacts GS21 and GS22 open the D.C. loop and this causes a high transient voltage across the contacts in a similar manner to that caused across the dial impulse contacts when dialling In the 400 type telephone these contacts were only partly quenched by the bell coil and series capacitor. In the 803 telephone, however, the new circuit uses the elements of the dial spark quench circuit, slightly re-arranged, for a second function as a spark quench or the gravity switch contacts.

The spark quench circuit applied to the dial impulse springs formed by the gravity switch contacts GS21 and GS22. In order to achieve this quenching it has been necessary to sequence the contacts GS3 and GS4 to break after contacts GS21 and GS22 as the handset is restored, The sequencing of the gravity switch contacts in this telephone is therefore opposite to that provided in the 400 type telephone. This is possible due to the provision of the shock absorbing rectifiers across the receiver which make sequencing for click suppression in the receiver unnecessary.

The dial spark quench circuit has been adjusted to an optimum value by insertion of R3 (22 ohm) between the gravity switch spring GS3 and the R3 terminal; the influence of R3 on the receiving transmission efficiency is negligible because of the relatively high impedance of the receiver.

The series connection of straps and links has been reduced to decrease fault liability at connecting points, but the inherent potential for circuit modifications has not been impaired.

TRANSMISSION PERFORMANCE
The circuit of the 801 telephone is based on the transmission circuit used in all modern instruments and first used in the Western Electric 500 telephone some 20 years ago.

The transducers used in the 801 telephone are the present standard Transmitter, Inset No. 13 and Receiver No. 4T. The dimensions of the handset which determine the position of the transmitter cup relative to tire receiver cap and have a big effect on the transmission performance, are in accordance with standards widely used in Europe.

The induction coil design minimises iron and copper losses and the magnetic reluctance of the air gap is chosen for maximum transmission efficiency under the "long loop" condition, consistent with adequate control of saturation by "zero-loop" feed current.

When receiving from the line, the signal divides between the transmitter and receiver and the ratio: "Audio signal power into transmitter" dived by "Audio signal power into receiver" equals "y" which is known as the "y" ration. When transmitting, the audio signal output of the transmitter is divided between "Line" and "Balance Network" and the ratio: "Audio signal power to Line" dived by the "Audio signal power to Balance Network" is also equal to "y". The value of "y" is determined by the ratio of coil windings, together with related line and balance network impedances.

Theoretically, maximum overall efficiency is obtained when "y" is unity but, to be compatible with an existing network in which receivers of low sensitivity such as type 1L are used, a telephone using a receiver with high sensitivity such as type 4T has to bias the "y" ratio to favour the transmitter. The departure from the 1:1 ratio introduces additional copper and iron losses in the induction coil, and the value of "y" chosen is a compromise which best fits the present transmission levels required in the Australian network. The winding ratios of the induction coil used in the 801 telephone are identical with those of British Post Office Coil, Induction No. 31 and almost the same as those of the British Post Office Coil, Induction No. 30 which was used in the 400 type telephone. As a result of [he gain in transmission by the use of more efficient transducers, modern telephones when connected by short lines have uncomfortably high "receive" volume and side-tone. On P.B.X. working an extension telephone may be connected to the local feeding bridge by a very short loop in the case of an internal call. but on a call over the exchange line the loop distance from the feeding bridge may be several miles.

Section missing

CONCLUSION.
The introduction of the 801 telephone has brought automatic subscribers instruments in Australia up-to-date by world standards, and plant in this field will now match the new types being introduced in the switching equipment and other fields. It is expected that this modern instrument will appeal widely to the general public as well as giving improved transmission performance and maintenance facilities.

Additional Pictures

The pictures below were taken by the British Post Office in 1964.  No doubt they were assessing the telephone probably for the APO and themselves.

Last revised June 24, 2025

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