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INSPECTION AND MAINTE-
The Receiver.-Receivers, on account of their location entirely outside the telephone case, are particularly exposed to injury. During the inspection trips, which should be made every three or four months, the receivers should be given special attention. The diaphragm cap should be unscrewed from the body of the receiver, and the diaphragm examined to see if it is bent or rusty; if either of these symptoms show up it should be replaced by a new diaphragm, but if apparently all right it should be dusted and used again. The strength of the permanent magnet should be tested by placing the diaphragm in contact with the pole faces; if a violent shaking of the magnet lengthwise fails to dislodge the diaphragm, the magnet is sufficiently powerful. Another method of testing the magnet consists in seeing if it will hold up the diaphragm by its edge. If the magnet fails to pass either of these tests, a new receiver should be substituted.
In reassembling the parts of the receiver, care must be taken to have the faces of the magnet exactly 3 inch from the diaphragm. This can be tested with the diaphragm off by placing a small flat stick across the circular support of the diaphragm and measuring the distance between the stick and the pole faces of the magnet. If the magnet is not in its proper position, it must be adjusted by turning it on the screw which holds it to the case. All parts must be perfectly clean when reassembled.
Receiver cords should be tested for a possible break or poor connection by listening in the receiver while the wire cord is moved or twisted; perfect receiver cords with clean bright tips securely connected to the binding posts are necessary for satisfactory operation. The sizzling sound sometimes heard in a receiver results from loose connections or from too strong a talking current rather than to a defect in the receiver. · The Transmitter.—Transmitters are less liable to get out of order than are receivers. Loose connections and too strong or too weak a battery current are often responsible for so-called transmitter troubles. If the current is too strong the carbon in the transmitter will heat, and if granulated carbon is used it will then become packed; on the other hand, too weak a battery current will give a weak transmission. Packing of the carbon granules can usually be overcome temporarily by lightly tapping the side of the transmitter, and permanently by using not more than two Fuller cells in series or their equivalent in the other forms of cells previously described.
In the Blake transmitter, it is very important that the contact between the platinum ball and carbon button be kept clean and in good condition; otherwise the sound will be scratchy. As the platinum ball by pressing against the carbon tends to roughen it, the latter should be rubbed occasionally with emery cloth and polished with a clean piece of paper. The platinum ball should also be polished, using unglazed writing-paper for the purpose. The springs must be left tightly clamped to their supports, and the final adjustments made by the bottom screw. If the sound is hollow the diaphragm should be given more play by loosening up the damper, and if there is a metallic pitch to the sound the diaphragm is probably bent.
The solid-back transmitter seldom requires attention. At times, however, the nuts at y, Fig. 11, binding the diaphragm at its center to the inner metal cone become loosened and have to be tightened, because the vibrations of the diaphragm are not then perfectly transmitted to the carbon, and the sounds are more or less indistinct. To tighten the nuts it is necessary to remove the metal cover rr from the case s by unfastening the screws around the outer edge. The nuts can then be loosened and the diaphragm adjusted to its proper place, after which the nuts may be tightened and the parts reassembled. If the diaphragm has been injured in any way, it is reached by following the instruc
tions just given, and should be replaced with a new one.
Poor transmission of speech is not always due to a defect in the transmitting devices. It may be caused by an improper use of the telephone as indicated in Fig. 59; in such a case the transmission will be indistinct and weak, no matter how good the transmitter and the other apparatus. Holding the transmitter against the breast as has
recently been advocated by some medical authorities, instead of in front of the lips, may have its advantages from a hygienic point of view, but the voice is not transmitted as clearly nor as well because in the former case the vibrations of the larynx must travel a comparatively long, obstructed route through the lungs, thoracic walls, and garments of the user instead of through a short free-air space in the latter case. Fig. 60 shows the proper way to use the transmitter in talking, to secure the best results.
The Battery.—Battery troubles generally arise from an exhausted battery solution, insufficiency of zinc, inferior quality of the plates, or from poor connections with the plates. An exhausted battery solution in the Leclanché cell is indicated by crystals collecting on the zinc; in the Fuller cell, by the color of the liquid becoming dark; and in the gravity cell, by the position of the dividing line between the two solutions being too high or too low. The dividing line should be kept about 1 inch above the copper plate either by replacing a portion of the zinc sulphate with water or by introducing more copper-sulphate crystals; the addition of the water will cause the dividing line to drop, and the addition of the crystals will cause it to rise. Dry cells become exhausted in from six months to a year and a half, depending upon how much the telephone is used; when they have become exhausted they should be replaced by new ones. During their useful life they require practically no tantetion. Porous cups in batteries should be renewed when they take on a rusty color.
Battery zincs require as much attention as the solution. When they become coated with salt, it is necessary to scrape and thoroughly clean them; if they have been much eaten away, new ones should be substituted. In purchasing new zincs, it is advisable to select only those having a light color and which give no indications of being porous, as they are then less liable to certain impurities. If the zincs are not amalgamated when purchased,