Common-Battery Telephone Sets

Owing to the fact that common-battery telephones contain no sources of current, they are usually somewhat simpler than the magneto type. The component parts of a common-battery telephone, whether of the wall or desk type, are the transmitter, receiver, hook switch, polarized bell, condenser, and sometimes an induction coil. The purpose of the condenser is to prevent direct or steady currents from pa ing through the windings of the ringer while the ringer is connected acro the circuit of the line during the time when the telephone is not in use. The requirements of common-battery signaling demand that the ringer shall be connected with the line so as to be receptive of a call at any time while the telephone is not in use. The requirements also demand that no conducting path shall normally exist between the two sides of the line. These two apparently contradictory requirements are met by placing a condenser in series with the ringer so that the ringer will be in a path that will readily transmit the alternating ringing currents sent out from the central-office generator, while at the same time the condenser will afford a complete bar to the pa age of steady currents. Sometimes the condenser is also used as a portion of the talking apparatus, as will be pointed out. Wall. In Figs. 151 and 152 are given two views of a characteristic form of common-battery wall-telephone set, made by the Stromberg-Carlson Manufacturing Company. The common-battery wall set has usually taken this general form. In it the transmitter is mounted on an adjustable arm at the top of the backboard, while the box containing the bell and all working parts of the instrument is placed below the transmitter, the top of the box affording a shelf for writing purposes. In Fig. 151 are shown the hook switch and the receiver; just below these may be seen the magnets of the polarized bell, back of which is shown a rectangular box containing the condenser. Immediately in front of the ringer magnets is the induction coil. IMG:384091999325875926_fig153_t.gif.png:Illustration_ Fig. 153. Stromberg-Carlson Common-Battery Wall Set Fig. 153. Stromberg-Carlson Common-Battery Wall Set View full size illustration. In Fig. 153 are shown the details of the circuit of this instrument. This figure also includes a simplified circuit arrangement from which the principles involved may be more readily understood. It is seen that the primary of the induction coil and the transmitter are included in series acro the line. The secondary of the induction coil, in series with the receiver, is connected also acro the line in series with a condenser and the transmitter. Hotel. Sometimes, in order to economize space, the shelf of common-battery wall sets is omitted and the entire apparatus mounted in a small rectangular box, the front of which carries the transmitter mounted on the short arm or on no arm at all. Such instruments are commonly termed hotel sets, because of the fact that their use was first confined largely to the rooms in hotels. Later, however, these instruments have become very popular in general use, particularly in residences. Sometimes the boxes or cabinets of these sets are made of wood, but of recent years the tendency has been growing to make them of pre ed steel. The steel box is usually finished in black enamel, baked on, the color being sometimes varied to match the color of the surrounding woodwork. In Figs. 154 and 155 are shown two views of a common-battery hotel set manufactured by the Dean Electric Company. Such sets are extremely neat in appearance and have the advantage of taking up little room on the wall and the commercial advantage of being light and compact for shipping purposes. A po ible disadvantage of this type of instrument is the somewhat crowded condition which nece arily follows from the placing of all the parts in so confined a space. This interferes somewhat with the acce ibility of the various parts, but great ingenuity has been manifested in making the parts readily get-at-able in case of nece ity for repairs or alterations. IMG:384091999325875926_fig154_t.gif.png:Illustration_ Fig. 154. Steel Box Hotel Set Fig. 154. Steel Box Hotel Set View full size illustration. IMG:384091999325875926_fig155_t.gif.png:Illustration_ Fig. 155. Steel Box Hotel Set Fig. 155. Steel Box Hotel Set View full size illustration. Desk . The common-battery desk telephone presents a somewhat simpler problem than the magneto desk telephone for the reason that the generator and local battery, the two most bulky parts of a magneto telephone, do not have to be provided for. Some companies, in manufacturing desk stands for common-battery purposes, mount the condenser and the induction coil or impedance coil, or whatever device is used in connection with the talking circuit, in the base of the desk stand itself, and mount the polarized ringer and the condenser used for ringing purposes in a separate bell box adapted to be mounted on the wall or some portion of the desk. Other companies mount only the transmitter, receiver, and hook switch on the desk stand proper and put the condenser or induction coil, or other device a ociated with the talking circuit, in the bell box. There is little to choose between the two general practices. The number of conducting strands in the flexible cord is somewhat dependent on the arrangement of the circuit employed. IMG:384091999325875926_fig156_t.gif.png:Illustration_ Fig. 156. Common-Battery Desk Set Fig. 156. Common-Battery Desk Set View full size illustration. IMG:384091999325875926_fig157_t.gif.png:Illustration_ Fig. 157. Bell for Common-Battery Desk Set Fig. 157. Bell for Common-Battery Desk Set View full size illustration. The Kellogg Switchboard and Supply Company is one which places all the parts, except the polarized ringer and the a ociated condenser, in the desk stand itself. In Fig. 156 is shown a bottom view of the desk stand with the bottom plate removed. In the upper portion of the circle of the base is shown a small condenser which is placed in the talking circuit in series with the receiver. In the right-hand portion of the circle of the base is shown a small impedance coil, which is placed in series with the transmitter but in shunt relation with the condenser and the receiver. IMG:384091999325875926_fig158_t.gif.png:Illustration_ Fig. 158. Bell for Common-Battery Desk Set Fig. 158. Bell for Common-Battery Desk Set View full size illustration. In Figs. 157 and 158 are shown two views of the type of bell box employed by the Kellogg Company in connection with the common-battery desk sets, this box being of pre ed-steel construction and having a removable lid, as shown in Fig. 158, by which the working parts of the ringer are made readily acce ible, as are also the terminals for the cord leading from the desk stand and for the wires of the line circuit. The condenser that is placed in series with the ringer is also mounted in this same box. By employing two condensers, one in the bell box large enough to transmit ringing currents and the other in the base of the desk stand large enough only to transmit voice currents, a duplication of condensers is involved, but it has the corresponding advantages of requiring only two strands to the flexible cord leading from the bell box to the desk stand proper. IMG:384091999325875926_fig159_t.gif.png:Illustration_ Fig. 159. Micro telephone Set Fig. 159. Micro telephone Set View full size illustration. A form of desk-telephone set that is used largely abroad, but that has found very little use in this country, is shown in Fig. 159. In this the transmitter and the receiver are permanently attached together, the receiver being of the watch-case variety and so positioned relatively to the transmitter that when the receiver is held at the ear, the mouthpiece of the transmitter will be just in front of the lips of the user. In order to maintain the transmitter in a vertical position during use, this nece itates the use of a curved mouthpiece as shown. This transmitter and receiver so combined is commonly called, in this country, the micro telephone set , although there seems to be no logical reason for this name. The combined transmitter and receiver, instead of being supported on an ordinary form of hook switch, are supported on a forked bracket as shown, this bracket serving to operate the switch springs which are held in one position when the bracket is subjected to the weight of the micro telephone, and in the alternate position when relieved therefrom. This particular micro telephone set is the product of the L.M. Eric on Telephone Manufacturing Company, of Buffalo, New York. The circuits of such sets do not differ materially from those of the ordinary desk telephone set. IMG:384091999325875926_fig160_t.gif.png:Illustration_ Fig. 160. Kellogg Common-Battery Desk Set Fig. 160. Kellogg Common-Battery Desk Set View full size illustration. IMG:384091999325875926_fig161_t.gif.png:Illustration_ Fig. 161. Dean Common-Battery Set Fig. 161. Dean Common-Battery View full size illustration.