(2) Because the line lamp is
associated closely with the line jack, it
usually is mounted in the switchboard
panel as part of the same unit with its
associated line jack, as in B. Here, a
signal lamp is shown in a two-contact
lamp jack below its associated line jack.
After the lamp is inserted in its jack, the
lamp entrance opening in the panel is
closed with a glass lamp cap, or opal, as
shown. The lamp cap may be color-
coded to indicate that a particular line
shall receive priority in the matter of
prompt service or that the station is
equipped to dial its own calls. Lamp
jacks, like line jacks, are mounted either
individually or in strips of 10 or 20, and
they are located either directly below or
directly above their respective line
jacks. The lamps illustrated in the
switchboard of figure 38 are located
above the corresponding line jacks.
FIGURE 44. Structure and Position of
Common-battery Telephone Sets.
Telephone sets in common-battery system contain most of the same components that are in the local-battery
telephone sets. The circuits connecting these components, however, differ considerably in the two systems. For this
reason, the telephone sets in figures 41 and 42 are shown only in block diagram form. It is now appropriate to consider
the circuits of common-battery telephone sets in detail.
a. Basic circuit of common-battery telephone set.
(1) The circuits of common-battery telephone sets may be classified as sidetone, or
booster circuits, sidetone-reduction circuits, and antisidetone circuits.
All three types, however,
are understood best by considering first a simpler and more fundamental circuit, basic to them all (fig, 45).