Western Electric 407A-4, Instruction Manual

Page: 69 / 136

to the final stage . Place the entire transmitter in opera­
tion. After a warming-up period at minimum plate voltage,
rais e the plate vo ltage to 16, 000 or 18, 000 volts and apply
excitation until the "Plate Current Vl" meter reads about
2
amperes . Check the 90-degree grid-c ircuit relation, making
a readjustment if necessary. Next ob serve the phase rela­
tion of the plate potentials of the two tubes, us ing the
"Vl Plate" and
11V2
Plate" jacks . Adjus t condenser ClD b y
means of the "Plate C ircuit Tuning
V2"
control for a 90-
degree phas e difference. This is the only control which
affects the relative phases of the plate potentials . Che ck
the adjustment of the "Plate Circuit Tuning " control on the
modulating amplifier . A new s etting of this control may be
neces sary with the Power .Amplifier in operation,
Condens er ClE is next tuned by means of the "Plate Cir­
cuit Tuning
Vl11
control until a cathode ray osci llos cope
connected to the
11Vl
Grid" and "Vl Plate" jacks shows a
straight line pattern, indicat ing a pure phase reversal in
the tub e .
With the two grid potentials 9 0 degrees apart and the
two plate potentials 90 degrees apart, and with a pure phas e
revers al in VlE, the grid and plate potentials of
V2D
should
now obviously be 180 degrees apart . This may be checke d
with the cathode-ray oscillograph using the
11V2
Grid" and
11V2
Plate" j acks .
Next increas e the excitati on until, with 18, 000 volts
plate potential� the output of the transmitter is the re­
quired 50 kilowatts , as indicated by meter J:12E " Transmis­
s ion-Line Current. "
At the 50-ki lowatt output check the phas e adjustments
and observe the plate currents of the tubes . The plate cur­
rent of
V2D
should be between 0, 5 and 0. 8 ampere and the
62