Western Electric 407A-4, Instruction Manual

Page: 34 / 136

connected across the 24-vol t supply through 11Lamp Reset" key
K3F.
The lamps are energized from the secondary of T2F
through the lamp contact of each relay.
Protective Circuit
The protective relay S3D operates to close its contacts
when any change occurs to disturb a balance between the in­
put and output circuits in the power amplifier. The nega­
tive side of the 24-volt circuit goes through the contacts
of S3D, then to the coil of relay SlOA. Positive of the 24
volts is supplied to the other side of the c
o
il and one arma­
ture of SlOA through disconnect switch Dl2F. The positive
side of the circuit continues through the back contact of
SlOA to the holding and operate windings of the lamp relay
S51F.
Plate Regulator
The plate-voltage regulator is a self-contained unit.
460-volt, 3-phase power is supplied from the distribution
cabinet to operate the motor. 230-volt single-phase power
is obtained from terminals 139F and 145F in the control unit
for the control circuit of the regulator. The normal con­
trol circuit of the regulator is completed through D8F in
the automatic position. If the control switch on the regu­
lator is left in the automatic position, either automatic
or manual operation may be selected at the control unit by
the operation of D8F. With D8F in the manual position,
K7F and K6F may be operated to energize directly the second­
ary relay of the regulator to raise or lower the voltage.
Note: The three indicating lamps should be removed
from the plate regulator at installation. Other­
wise lamps E28F and E29F in the control unit�
will not operate properly.
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