Circuits of Complete Switchboard.  We may now discuss the circuits of a complete simple magneto switchboard.  The one shown in Fig. 273 is typical.  Before going into the details of this, it is well to inform the student that this general form of circuit representation is one that is commonly employed in showing the complete circuits of any switchboard.  Ordinarily two subscribers’ lines are shown, these connecting their respective subscribers’ stations with two different line equipments at the central office.  The jacks and signals of these line equipments are turned around so as to face each other, in order to clearly represent how the connection between them may be made by means of the cord circuit.  The elements of the cord circuit are also spread out, so that the various parts occupy relative positions which they do not assume at all in practice.  In other words it must be remembered that, in circuit diagrams, the relative positions of the parts are sacrificed in order to make clear the circuit connections.  However, this does not mean that it is often not possible to so locate the pieces of apparatus that they will in a certain way indicate relative positions, as may be seen in the case of the drop and jack in Fig. 273, the drop being shown immediately above the jack, which is the position in which these parts are located in practice.

[Illustration:  Fig. 273.  Circuit of Simple Magneto Switchboard]

Little need be said concerning this circuit in view of what has already been said in connection with Figs. 240 to 245.  It will be seen in the particular sub-station circuit here represented, that the talking apparatus is arranged in the usual manner and that the ringer and generator are so arranged that when the generator is operated the ringer will be cut out of circuit, while the generator will be placed across the circuit; while, when the generator is idle, the ringer is bridged across the circuit and the generator is cut out.

The line terminates in each case in the tip and sleeve contacts of the jack, and in the normal condition of the jack the line drop is bridged across the line.  The arrangement by which the drop is restored and at the same time cut out of circuit when the operator plugs in the jack, is obvious from the diagrammatic illustration.  The cord circuit is the same as that already discussed, with the exception that two ringing keys are provided, one in connection with the calling plug, as is universal practice, and the other in connection with the answering plug as is sometimes practiced in order that the operator may, when occasion requires, ring back the calling subscriber without the necessity of changing the plug in the jack.  The outer contacts of these two ringing keys are connected to the terminals of the ringing generator and, when either key is operated, the connection between the plug, on which the ringing is to be done, and the rest of the cord circuit will be broken, while the generator will be connected with the terminals of the plug.  The listening key and talking apparatus need no further explanation, it being obvious that when the key is operated the subscriber’s telephone set will be bridged across the cord circuit and, therefore, connected with either or both of the talking subscribers.