Western Electric 407A-4, Instruction Manual

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sive current drawn from the rectifier and to open the high­
vol tage circuit breaker. Resistance R2G may be used to ad­
just the operate point of this relay.
Protection from accidental contact with the high-volt­
age circuits of the rectifier and other apparatus within the
main enclosure is afforded by the mechanically interlocked
switches DlG, D2G, and D3G, which are operated by a hand­
wheel located at the 5-kw enclosure gate. When operated to
open the gate, D3G opens the circuit of the transmitter gate
switches, which in turn opens the high-voltage circuit
breakers; DlG then grounds the high-voltage supply circuit
to the rectifier and also the output circuit of the recti­
fier; finally D2G energizes the door-lock circuits of Units
C and G.
A single-phase full-wave bias rectifier, using two
mercury-vapor tubes, is also mounted in this assembly. This
rectifier supplies grid bias potential to the two water­
cooled vacuum tubes of the D-151135 Modulating Amplifier,
for 5-kw emergency operation. Relays S3G and S4G transfer
the bias connection on Unit C, between Unit K (for 50-kw)
and Unit G (for 5-kw). Switch D5G serves to close the three­
phase supply to the rectifier for reduced power operation;
for 50-kw operation this switch is normally open. Switch
D6G is the 50-5 kw transfer switch, operation of which en­
ergizes one or the other of each of several pairs of con­
tactors which complete the control, power supply, bias, and
radio-frequency circuits as required for either operating
condition.
Special D-99116 Control Unit and Control Circuits
(Unit F, Schematics Figures 4 and 5)
General
The special D-99116 control unit is the center of the
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