A NEW SMALL-SIZE TELEPHONE
The article describes a new telephone set recently developed by the Company to meet the increasing demand for a versatile instrument of small size, light weight and pleasing appearance.
Named the ‘Etelux’, and available in a range of attractive light-fast colours, this easy-to-handle, compact telephone has a flexibility of design permitting the provision of all types of conventional service for both residential and business subscribers. Equally suitable on table or wall, the new set may be used as a simple extension instrument with or without ringer, or may be connected directly to auto,
CB exchange lines or 2-party lines including those with party identification facilities; (e.g. Dial Message Rate, Auto Ticketing,
2nd-Tip Party etc.). The transmission performance conforms with B.P.O. and international standards, and the components used throughout are designed to give efficient trouble-free service under temperate or tropical
conditions. Dial illumination is provided as an optional extra.
Among the many factors that contribute to the popular acceptance of a modern telephone, attractive appearance and convenience of use stand in prominence. To an Administration, an instrument incorporating these features must be suitable for table or wall use, easy to install and maintain, in limited space if necessary, and have a high standard of transmission efficiency over short or long lines. Furthermore, the basic design must enable optional features to be added to meet a subscriber’s particular needs. From the user’s standpoint, the telephone must be available in a range of colours to suit personal tastes, and small enough to be placed in a position where space may be limited. In particular, the instrument must be easy to operate wherever installed, or even when held in the hand.
These points were kept in mind in designing the Etelux. The end result has been a small, lightweight, efficient telephone set of distinctive appearance and flexible design, suitable for all conventional types of service. Because of its small size, it is ideally suited for convenient use on small desks and tables or when mounted on the wall. A typical location is shown in Figure
The carefully selected soft-tone colours in which the Etelux is offered to meet the varying requirements of different decorative schemes are:-
AQUA JADE, LIGHT IVORY, ALICE BLUE, ROSE GREY, DUSKY PINK
The new set is approximately one third the size and less than two thirds the weight of a conventional table instrument. These considerable reductions are due largely to the use of reinforced plastic for the outer shell and base, the avoidance of any metal chassis for component mounting, and the application of standard but lightweight components. An additional and important influencing factor was the decision to provide the ringer assembly as a separate unit to give the telephone greater flexibility of use.
In the design of the Etelux, both external appearance and ease of use have received as much specialized attention as the instrument’s technical performance. The low aspect and simple lines of the set are emphasized by the smooth blending of handset, dial and cover, and by avoiding the total concealment of the base when the cover is in position. To simplify cleaning, all exposed surfaces of the instrument are smooth.
The cover and cradle is a one-piece moulding of a plastic copolymer (acrylonitrile-butadiene-styrene), a tough yet lightweight scratch-resistant material,
incorporating the important characteristic of good colour stability and capable of withstanding very rough usage without damage. The wells formed in the cover are so designed as to provide a stable rest position for the handset, and the slightly recessed areas at the front and rear of the cover provide an effective handhold for lifting the telephone complete. When lifted, the set may be held comfortably in the palm of the hand, the handset removed and a number conveniently dialled.
The lightweight and comfortable handset is moulded of the same material as the cover and conforms in general shape and features to that of the Etelphone, with the exception of the mouthpiece. This has the usual acoustic cavity and customary annular pattern of holes, but has no lip; this ensures that the handset falls into the correct position in the cover wells when it is replaced after use. The transmitter capsule is of the immersed-electrode carbon granule type, and the receiver capsule of the rocking-armature pattern. These components, combined with others in the telephone circuit give a transmission performance equal to B.P.O. and international standards.
The cover fits closely to the base by concealed mating surfaces and is secured by two captive screws in metal inserts in the cover moulding. When the screws are released, the cover can be lifted clear to reveal all components on the base, as shown in Figure
2 (below), thus simplifying adjustment and maintenance.
The base, insert-free and with an area little more than half that of a standard instrument, is moulded in a tough resilient grade of polystyrene. Its exposed portion is finished in a light beige colour, blending well with the instrument’s colour range. Terminal strips, provided in ribs moulded into the base, are distributed around the inside edge of the base for ease of access. Simple ‘break-ins’ at each end provide choice of entry for the line wiring.
Because of the light weight of the telephone, special attention had to be paid to prevent the instrument from slipping during dialling. This
difficulty was overcome by covering the underside of the base with a neoprene mat, moulded with a waffle pattern on its bottom surface. In addition to resisting the movement of the telephone, the mat also serves to prevent damage to polished surfaces on which the telephone may be standing.
A simple design of cradle switch is employed. The switch consists of a spring-loaded plunger bracket and an associated comb-operated springset, both arranged on a common mounting plate riveted to the base. The plunger bracket, pivoted on two uprights of the mounting plate, has on its transverse bar a lower projection bearing directly against the contact-operating comb of the springset when the telephone is idle. At each end of the transverse bar, two arms extend in the horizontal plane and are so shaped at their ends as to firmly engage the slots formed in the underside of a single clear plastic
plunger. This operates with an adequate margin of safety on contact of earpiece or mouthpiece when the handset is replaced, and slides freely within the limits allowed by its elongated slot which moves about a metal guide pin inside the cover. A liberal plunger slot in the cover well and sufficient restoring-spring pressure eliminate any possibility of plunger sticking, and ingress of dust through the slot is minimized by projecting flanges on the plunger which bear against the inner surface of the cover when the handset is removed.
The cradle switch springs are nickel silver, with twin palladium contacts, and the specified pressures are ample to ensure reliable connection. Protection of the contacts from dust is provided by a transparent clip-on cover.
When the instrument is assembled, the dial is slightly recessed in the cover. Because of this,
the needed mechanical protection of the dial is automatically obtained, inadvertent rotation of the finger-wheel minimized, and a more streamlined appearance secured. A further contribution from the appearance standpoint is the pleasing
silver gilt finish of the plastic finger-wheel.
For convenience of viewing and ease of use, the dial is offset at a slight angle and, on a table set, the designations on the number plate are positioned above centre since the dial is normally seen from a relatively low angle. Conversely, when the set is converted for wall use, the dial characters are arranged below centre.
To ensure reliable operation, the dial mechanism and springsets are protected by a transparent cover, and palladium is used for the pulsing contacts to avoid high contact resistance.
When required, low-voltage dial illumination can be provided. This is a useful feature allowing easy location of the instrument in the dark or the set to be used in conditions of half-light where it is difficult to read the dial characters. The illumination is provided by a small flash-light type bulb, mounted on a hinged trap in the base and positioned beneath the number-plate in the region underneath the 8 and 9 holes of the finger-wheel. The lamp is readily replaceable by the subscriber, since the hinged trap is easily raised, being designed to accept the tip of the finger or a small coin.
The number-plate, uniformly lit over its entire area, is a relatively thin piece of plastic, painted translucent white and having black moulded-in characters on the back to prevent defacement by use. Subdued illumination is provided when the telephone is idle, but on removal of the handset the light is intensified to full brilliancy. A slide switch, placed conveniently to hand in the base, enables the user to switch the subdued light on or off to suit personal preference.
Power for the lamp is obtained from a 6-volt transformer plugged into the mains. This transformer, because of differing voltage supplies and outlet sockets at subscribers’ premises, is not supplied with the instrument, but may be purchased locally where conditions and requirements are known.
Provision is made for the inclusion of a press key adjacent to the dial-light switch so that a number of special service features can be added
according to the needs of the subscriber. The key, similar to the dial-light switch but with a non-locking action, may be employed for party-line working or to provide operator re-call or transfer facilities.
The transmission components on the base comprise an induction coil, capacitors and resistors. Because of the sensitivity of the transmission circuit an auto regulator unit and click suppressor are also included.
The regulator unit, clearly seen in the right-hand corner of the base (Figure 2) enables the installer to adjust the line current for best transmission whether the line is short or long, thus ensuring all-round efficiency on both local and long-distance calls. The printed-wiring layout of the unit is connected to the telephone circuit by a single lead of the handset cord and by four terminal screws which also serve to retain the unit in position. With this method of fixing, the need for plug-in contacts is avoided and thus the electrical efficiency of the regulator is unaffected by adverse atmospheric conditions.
When the regulator is not required, it is a simple matter to withdraw the device and terminate the handset-cord lead to another terminal provided for this purpose.
The click suppressor, consisting of a simple rectifier arrangement, is connected across the receiver circuit to prevent any risk of an acoustic shock to the user, arising from the inevitable pulses of energy applied to the line by switching operations.
Wiring and Cords
The telephone is wired with p.v.c. insulated wire in various colours, allowing ready identification. With the exception of stranded wire used for connections to the dial, all other terminations are made by
6.5 lb/mile wire.
Both the line and handset cords are designed for long and trouble-free service even under tropical conditions. The extensible handset cord is of the ‘soft-pull’ type and capable of extending six feet without exerting considerable pull on the telephone. It has, in common with the line cord, spade-shaped tags for easy termination or removal, and p.v.c. insulated leads covered overall with an outer layer of clear plastic insulation. The leads are marked at regular intervals throughout their
entire length with individual identification colours and these, visible through the transparent outer covering, present an unusual but very attractive appearance.
Connections of the line cord to the incoming line are made via the terminal strip in the ringer unit. Alternatively, when the instrument is used as a simple extension and the ringer unit dispensed with, connections are completed at a small, unobtrusive terminal box moulded in reinforced polystyrene.
Cord anchors hold the cords at their entries in the telephone, handset, and ringer unit or terminal box, thus preventing strain on the conductors.
The ringer unit designed for use with the Etelux has overall dimensions 6 ins, long,
3.5 ins, wide and l.8 ins, deep (152 x 89 x 48 mm.) and consists of a single-gong ringer assembly, together with a
7 terminal connecting strip for the termination of line
cord, line wires and lamp leads. The terminal strip is arranged above the ringer; both units are mounted on a rigid zinc-plated metal baseplate and enclosed by a robust plastic cover (coloured beige) secured to the base by a captive screw.
Twin coils are used in the ringer, each coil being of a value permitting the same ringer and telephone to be used for individual or 2-party lines, including those requiring party identification facilities. Simple adjustment of strapping in the telephone introduces the appropriate arrangement. Where party-line working is not required, coils of various standard resistance values may be fitted to suit an Administration’s particular needs.
When the instrument is for party-line application, the ringer can be supplied biased to prevent the bell from tinkling when dialling is in progress on the partner telephone. A feature of the bias spring is that its adjustment is not restricted to the usual choice of a given number of positions, since the spring is so
arranged as to permit its movement by finger-tip pressure to any position between the non-bias and full bias locations. Thus, exact bias can be applied.
To permit the loudness of the bell to be adjusted to a suitable level, for reasons of convenience or where noise must be kept to the minimum, ringing-volume control is provided by an adjustable lever located at one end of the base.
The Etelux as a wall-mounted telephone is shown in Figure 3 (right). Its conversion from table to wall use is a simple matter, requiring the fitting of a cradle bracket to ensure stable vertical hang-up, and the changing of the dial number plate for another to give increased visibility of the dial characters. For dial-light telephones a wall-fixing bracket is also required.
Instruments can be supplied complete as wall telephones or, alternatively, to suit Administrations wishing to stock table instruments only, and subsequently convert as requirements demand, the appropriate parts can be made available to allow conversion operations to be done at some convenient central location. With the set of parts, a simple template is included to facilitate the correct drilling of the two holes necessary to accommodate the cradle bracket, as shown in Figure 4.
When a dial light is included, the instrument is mounted on a double folding bracket, hinged at its lower end. By releasing one small captive screw in the apex of the mounting, the bracket can be opened out to bring the telephone forward and provide easy access to the base for replacement of the dial lamp in the event of failure.
The Etelux is a further step forward to the improvement of the telephone, particularly from the standpoint of appearance and its capability to make the chore of telephoning as effortless as possible. The high degree of flexibility maintained in its basic design must also be considered a major contribution to this end.
While it is not possible at this early stage to assess the full appeal of the new instrument, several Administrations, after proving the instrument to their own satisfaction by extensive field trials, have already decided to adopt
it to meet the special requirements of discriminating subscribers. Because of this, it is confidently felt that similar decisions will be made by other Administrations in the near future, thus proving beyond doubt the popular acceptance of the Etelux.