Western Electric 407A-4, Instruction Manual

Page: 51 / 136

elements of the tubes after shipment or handl ing, thus mini­
mizing the pos s ibility of flashovers . With the "Oscillator­
Amplifi er Control 11 switch, DllF, of the spe cial D-99116 con­
tro l unit in the "Test" position there is no automatic delay
for the protection of the recti fi er tubes . Under these con­
diti ons a filament
time of at least 1 5 s ec onds should
be al lowed before applying the plate
After the 702A oscillators have been ins erted and the
heater power has been applied by placing the 110s c . Heater"
switch in the 110N11 position, the indicator lights wi ll be on
cont inuously until the unit has reache d the normal operating
temperature
(
approxLmately 60 degrees C entrigrade
)
as indi­
cated by the thermometer . When starting from normal ro om
temperature this time should be approximately one hour .
Thereafter the lights should be alternately "ON" and "OFF"
for per iods of about 30 seconds , the exact time depend ing
upon the amb ient temperature .
Make preliminary adjustments of the radi o-frequency
circu its according to Tab le 3 .
First Radio-Frequency Amplifier
Res onance is obtaine d in all plate circuits by an ad­
jus tment for minimum d-c plate current of the tube whos e
tune d output circu it is being adj us ted. In tuning any of
the radio-frequency circuits , care should be taken that no
circu it is tuned to the s econd harmonic of the fundamental
frequency. Should two points of resonance be found with
coarse adjustment as specified, the one at whi ch the capac­
itance of the variable condenser i s ma.x i:rrru.m is the co rrect
adj ustment. This will correspond to the point of higher
dial reading and higher output current .
Before applying plate vo ltage open links D6A and D7A.
Place the "Plate Rectifier" switch in the "ON" position and
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