Grounds, grounded elements, and returns
Heaters or filaments, off ground
Power supply, B plus
Power supply, minus
AC power lines
Miscellaneous, above or below ground returns, AVC, etc.
Figure 6-15.Wiring color code for electronic equipment.
BLOCK NUMBERING SYSTEM.Parts
designations in figures 6-11, 6-12, and 6-13 were
made according to the block numbering system, which
is no longer in use. In that system, a letter identifies
the class to which a part belongs, such as R for resistor,
C for capacitor, V for electron tube, and so on. A
number identifies the specific part and in which unit
of the system the part is located. Parts within each
class in the first unit of a system are numbered
consecutively from 1 through 199, parts in the second
unit from 201 through 299, and so on.
UNIT NUMBERING SYSTEM.In this cur-
rently used reference designation system, electronic
systems are broken into sets, units, assemblies, subas-
semblies, and parts. A system is defined as two or more
sets and other assemblies, subassemblies, and parts
necessary to perform an operational function or func-
tions. A set (fig. 6-16) is defined as one or more units
Figure 6-16.A five-unit set.