Note. Failure or unsatisfactory performance of equipment used by Army Ground
Forces and Army Service Forces will be reported on wD. AGO Form 468 Un
satisfactory Equipment Report) ; by Army Air Forces, on Army Air Forces Form
54 (Unsatisfactory report). If neither form is available, prepare the data
according to the sample form reproduced in rigure 34.
Section I. THEORY OF TELEPHONE EE-8-(*)
43. Circuit Elements
a. Handset TS-9-(*).
Handset TS-9-(*) contains a high output
nonpositional transmitter and a high fidelity receiver. The transmitter
element is of the granular carbon type. The diaphragm, carbon inclosure,
and frame are constructed in unit form making the element readily
replaceable. The receiver element is a permanent-magnet, diaphragm
type. It gives high fidelity response over the audible frequency range, and
is effectively compensated for stable performance over a wide tempera
b. Generator (fig. 24).
Generator GN-38 has three small cobalt steel
permanent magnets arranged in two pole faces about an armature.
Generator GN-38-A has a rotating magnet with stationary coils. Gen
erator GN-38-B has two stationary magnets and two pole pieces ar
ranged alternately about an armature. The generator switch consists of
spring contacts which in normal position connect the ringer across the
line, but which upon rotation Of the crank disconnect the ringer and
place the output of the generator across the line. The crank handle folds
into the metal-faced recess on the right side of the case.
Ringer MC-131 is of the single-gong type. The ringer
coils, armature, and clapper are mounted internally to the gong (figs. 6.
7. 8. and 20). When energized by ringing current, the armature operates
the clapper about a pivot to strike alternately two internal projections of
the gong rim. The acoustical output is high for a relatively low electrical input.
d. Holding coil.
The holding coil (Coil C-158) is bridged across
the line circuit when the screw switch is in the CB position and the
lever switch is released. With the lever switch depressed, the coil is
disconnected. If the screw switch is in the LB position, the coil is permanently
disconnected, independent of the lever switch position. The
purpose of this coil is to provide a low resistance d-c path through the
telephone for operating the line relay and holding the supervisory relay
energized on a common battery switchboard. The holding coil has high
impedance to voice-frequency currents to minimize transmission losses.
e. induction coil.
The induction coil (Coil C-105) is an autotrans-
former with one continuous winding tapped at terminals 2 and 3 so as
to form the 1-2 section, the 2-3 section, and the 3-4 section. ( See figs. 25
f. Lever switch.
The lever switch has two contacts which are
operated by a hinged lever and plunger. The switch is held depressed
by the weight of the handset which is hung on it. and is automatically
raised by a spring when the handset is removed. The contacts are open
when the lever switch is depressed and closed when the switch is released.
The lever switch is used only on common battery circuits.
In Telephone EE-8, three physically separate capaci
tors, of 1.9-mf, 0.5-mf. and 0.3-mf capacitance are used. ( See figs. 25
and 27.) In Telephones EE-8-A and EE-8-B. Capacitor CA-355 com
prises a 2.0-mf. a 0.5-mf, and a 0.3-mf capacitance element, all assembled
into one container and internally connected to the terminals numbered
1. 2. 3, and 4. (.See figs. 26, 28, and 29.)
44. Theory of Operation
The schematic diagram of Telephone EE-8 is shown in figure 25 and the
schematic diagram of Telephones EE-8-A and EE-8-B is shown in
a. Transmitting circuit.
The transmitter, receiver, induction
coil, and the 0.3-mf capacitor are connected in an antisidetone circuit
in which the impedance of these elements and the characteristic im
pedance of the average line (Wire W-110-B) are so balanced as to reduce
the sidetone in the receiver to the proper level. This results in an
effective gain since the effect of noise in the vicinity of the transmitter
of the receiving telephone is reduced. The user also unconsciously speaks
more loudly into the transmitter when he does not hear his own voice
loudly in the receiver. This results in effective transmitting gain. On
lines shorter than the average, the sidetoue is more pronounced and
the antisidetone effect is lessened.
the entire 1-4 winding of the induction coil and across terminals L1 and
L2 to which the line is connected.
The antisidetone operation of the circuit results from the elec
trical balance between the impedance of the 3-4 section of the induction
coil in series with the 0.3-mf capacitor, and the impedance of the line
circuit consisting of 4 miles or more of Wire W-110-B connected to
terminals L1 and L2. On shorter lines the antisidetone is less pro
nounced, although still effective.
b. receiving circuit.
The induction coil, 0.3-mf capacitor,
and receiver are so designed that the greater portion of the incoming
line current will flow through the receiver over the voice-frequency
range. This results in a maximum sound output.
The 0.5-mf capacitor is placed in series with the receiver to
prevent the flow of direct current through the receiver, either from
the batteries in the telephone or from the central office battery, when the
telephone is connected to a common battery system. This capacitor also
limits 16-cycle ringing current through the receiving circuit and permits
the permanent connection of the listening circuit across the line.
The transmission loss through the ringer, or the ringer and the
capacitor in series, and the holding coil is negligible because of the high
impedance to voice-frequency currents of these elements.
c. signaling circuit.
The 1.9-mf capacitor in Telephone EE-8,
or the 2.0-mf capacitor in Telephones EE-8-A and EE-8-B, is in series
with the ringer when the screw switch is in the CB position. This
capacitor prevents direct current from biasing the ringer and also pre
vents the ringer from interfering with d-c signaling or supervision when
the telephone is connected to a common battery system. The capacitor is
short-circuited when the screw switch is turned to the LB position.