Western Electric Receiver.  The standard bi-polar receiver of the Western Electric Company, in use by practically all of the Bell operating companies throughout this country and in large use abroad, is shown in Fig. 50.  In this the shell is of three pieces, consisting of the barrel 1, the ear cap 2, and the tail cap 3.  The tail cap and the barrel are permanently fastened together to form substantially a single piece.  Two permanently magnetized bar magnets 4-4 are employed, these being clamped together at their upper ends, as shown, so as to include the soft iron block 5 between them.  The north pole of one of these magnets is clamped to the south pole of the other, so that in reality a horseshoe magnet is formed.  At their lower ends, these two permanent magnets are clamped against the soft iron pole pieces 6-6, a threaded block 7 also being clamped rigidly between these pole pieces at this point.  On the ends of the pole pieces the bobbins are wound.  The whole magnet structure is secured within the shell 1 by means of a screw thread on the block 7 which engages a corresponding internal screw thread in the shell 1.  As a result of this construction the whole magnet structure is bound rigidly to the shell structure at a point close to the diaphragm, comparatively speaking, and as a result of this close coupling, the relation between the diaphragm and the pole piece is very much more rigid and substantial than in the case where the magnet structure and the shell were secured together at the end farthest removed from the diaphragm.

[Illustration:  Fig. 50.  Western Electric Receiver]

Although this receiver shown in Fig. 50 is the standard in use by the Bell companies throughout this country, its numbers running well into the millions, it cannot be said to be a strictly modern receiver, because of at least one rather antiquated feature.  The binding posts, by which the circuit conductors are led to the coils of this instrument, are mounted on the outside of the receiver shell, as indicated, and are thus subject to danger of mechanical injury and they are also exposed to the touch of the user, so that he may, in case of the wires being charged to an abnormal potential, receive a shock.  Probably a more serious feature than either one of these is that the terminals of the flexible cords which attach to these binding posts are attached outside of the receiver shell, and are therefore exposed to the wear and tear of use, rather than being protected as they should be within the shell.  Notwithstanding this undesirable feature, this receiver is a very efficient one and is excellently constructed.

[Illustration:  Fig. 51.  Kellogg Receiver]