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Page Title:
If. Amplifier Alignment, Tuning Unit I, General |
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|  After proper a d j u s t m e n t i s
slotted shaft of R762 to obtain an
o b t a i n e d , disconnect the leads of
i n d i c a t i o n of +420 volts dc with
the ac vtvm from the transformer -
r e f e r e n c e to ground on the multi-
terminals.
m e t e r . This step sets the positive
c . Electrometer Filament- Voltage Ad-
voltage that is fed to the impulse
justment.
generator contact. R e m o v e the
C a u t i o n : If these adjustments are not
m u l t i m e t e r leads after proper in-
m a d e properly, the electrometer circuit
dication has been observed.
may become damaged.
Set POLARITY switch S709 at -.
(5)
(1) Set the dc vtvm to the 3-volt scale.
Reconnect the multimeter as
(6)
d i r e c t e d in procedure (2) above,
(2) Turn the ELECT. V3 ADJ control
with the FUNCTION switch set to
(3) Connect the leads of the dc vtvm
the REV. position.
a c r o s s terminals 8 and 10 on the
O b s e r v e the multimeter for an in-
(7)
filter box ii t the rear of the main -
d i c a t i o n of -420 volts with refer-
ence to chassis ground. If the
connect the positive voltmeter lead
a m p l i t u d e is not the same as that
to terminal 8, and the negative lead
o b t a i n e d in procedure (4) above,
to terminal 10.
vary the shaft of R762 to obtain the
(4) Adjust the ELET. 1 73 .4UJ control
s m a l l e s t difference in amplitude
for a 1.2-volt indication on the dc
between the positive and the nega-
vtvm.
t i v e voltages in each of the two
( 5 ) Turn the ELECT. V4 MM control
p o s i t i o n s of S709. After satisfac-
f u l l y clockwise and move the dc
t o r y adjustment, remove the mul-
vtvm leads! to terminals 11 and 9
t i m e t e r leads.
on the filter box. Be sure to con-
(8)
Use the following chart to check the
nect the positive voltmeter lead to
potentials present on the terminals
terminal 11, and the negative lead
of POLARITY switch S709.
t o terminal 9. Adjust the ELECT.
V4 ADJ control for a 1.2-volt in-
dication on the dc vtvm.
84. If. Amplifier Alignment, Tuning Unit
1, General
a. TO align a tuning unit, remove its
dust cover. Use the test harness (fig. 46)
to interconnect the tuning unit to the main
b. Filament-Voltage B a 1 a n c e Adjust-
u n i t . Tuning unit 1 uses two separate if.
ment (fig. 55).
amplifier subassemblies; one is tuned to a
(1) S e t the ac vtvm to the 110-volt
center frequency of 455 kc, and the other
scale. Connect one lead to chassis
is tuned to 1,600 kc. All if. transformers
ground and the other alternately to
are tuned by means of movable iron cores.
terminals 14 and 16 of transformer
For ease of setting, the tuning adjustments
T702.
a r e terminated with an integral 1/4-inch
(2) R 7 0 6 is a variable resistor which
hexagonal nut. The use of a plastic align-
is connected across the heater pins
m e n t tool (6-8 inches long) will prevent
o f audio amplifier V701. The arm
o f this variable resistor is acces-
c a p a c i t a n c e effects during alignment. The
f o l l o w i n g chart indicates which if. trans-
sible from the top of the main unit
f o r m e r s require tuning only from the top
c h a s s i s . Adjust R706 so that the
of the if. chassis, and which require tuning
v o l t a g e from terminal 14 of T702
of the cores from both the top and bottom
t o ground is equal to the voltage
of the if. chassis.
from terminal 16 of T702 to ground.
192
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