hand generator of telephone A generates an alternating current which is conducted by the telephone line to the ringer of
telephone B and causes it to operate. The switches referred to are not shown in the illustration. A similar circuit exists
between the hand generator of telephone B and the ringer of telephone A.
b. Components of telephone set. The components of a local-battery telephone set, excluding the handset, are
shown in figure 29. In addition to the hand generator, the battery, and the ringer, there are an induction coil and a
capacitor to improve electrical efficiency and performance.
The function of the battery in the local-battery telephone set is to supply the current for the transmitter. The
battery consists of two or three dry cells, which obtain their electrical energy from the chemical action of the materials of
which the cell is composed. The chemical action during current flow produces an accumulation of gas bubbles around the
positive electrode, which insulates the electrode and increases the internal resistance of the cell. This action of the cell is
called polarization. The manganese dioxide contained in the dry cell neutralizes the polarization, but its action is slow,
and a continuous drawing of current causes the emf of the cell to fall rapidly. If the cell is given a short rest, however, the
depolarization reaction catches up, and the emf increases to nearly its original value. Dry cells therefore are suited
particularly for intermittent use. The emf of a new dry cell is about 1.53 volts, and it decreases with age.
a. Function. A handset switch is usually a normally open, momentary (spring-return) switch. When pushed, it
connects the transmitter in the talking circuit. When released, the transmitter is out of the circuit, thus conserving the
battery when the transmitter is not in use.
b. Push-to-talk handset switch. A, figure 30, illustrates a handset switch of push-to-talk type, frequently used in
local-battery telephone sets. It consists of an assembly, or pile-up, of flat, spring-metal conductors, separated by
insulators, as in B. Welded to the ends of the conductors are contacts made of a special alloy which withstands arcing
when the switch is opened and closed. The contacts are closed by rotation of the butterfly nut attached to the short shaft
which passes through the plate.