Receiver Alignment; 12 3. Noise Limiter And Avc Amplifier Adjustment O - Hallicrafters SUPER SKYRIDER SX-28-A Instruction Book

D
RECEIVER ALIGNMENT
Equipment Needed for Aligning:
I-Art all wave signal generator which will provide
an accurately calibrated signal at the test frequencies
indicated.
2-output indicating meter connected to 5000 ohm
output terminals.
3-Non-metallic screw driver.
4-Dummy antenna of 200 mmf and also 400 ohm
carbon resistor.
Setting of controls
p~ior
to alignment-IF and RF.
Tone control at maximum high frequency position
(#9)-BFO at o-Bass switch at Bass IN-AF Gain at
#9--RF Gain at #9--Band switch-IF alignment posi-
tion ,55 to 1.6 band-RF alignment depending on band
aligned.
Selectivity control at sharp
IF-~nd-Receive
switch
in Receive---Crystal phasing at #3 on left side-ANL--
OFF at o-A VC OFF.
Important: Have bandspread control so logging scale
reaas 100.
Antenna trimmer adjusted for Maximum gain at each.
RF alignment point on.
all
bands.
(1)
455 KC-IF Alignment: Tune main dial to 1400 kc on
.55 to l.(5.mcband. Connect the hot lead from the signal
genera tot to 6SA 7 mixer terminal IS-Ground to chassis.
Roughly adjust the aligning screws of Tl, the lower
screw of which is accessible through hole in right mount-
ing bracket, for maximum gain. Now adjust lower screw
on T2 (do not adjust upper screw). Also adjust C31 and
the air trimmer condensers at the top of T3 for maximum
gain. (See Fig. 8 for location of IF adjustments)
Switch to Crystal Broad Position-Turn on BFO and
adjust to a tone of about 1000 cycles. Vary the frequency
of the signal generator while adjusting the top screw on
1'2 until the 4)utput goes through a maximum, dips down
and starts going up again. Adjust th!! phasing control
for maximum selectivity and then back off the top screw
on T2 until the output reaches a minimum value between
the tWo maximum values first noted. The frequency of
the signal generator should be varied over a small range
while adjusting the top screw of T2. A swishing note,
in. contrast to the usual sharp crystal tone will be ap-
parent when the correct adjustment has
be~n
reached.
Switch to "Xtal Sharp" and adjust C-
30
for maximum
output while varying signal generator frequency. Two
points of maximum output will be noted corresponding
to
two adjustments 0(C-
30 .
Either one of these points
may be used at which to leaveC-
3o •
a sharply peaked
tone will result at the correct adjustment.
Switch to "Xtal Medium" and adjust
(:-Z9
till .the
output is midway between the outputs reache4 while
aligning the "Xtal Sharp" and "Xtal Broad" positions.
The apparent sharpness of tone should be.midway be-
tween the "Sharp" and "Broad" positions.
Switch again to "Xtal Sharp" and set the signal gen-
erator to exact crystal frequency. Set BFa front panel
control
to
a tone. of approximately 1000 cycles. Switch
again to "Sharp IF" and carefully realign the IF trans-
formers as earlier described in the 6rst paragraph of these
instructions.
(2)
BFa Adjustment: Set front panel control to zero-BFa
switch ON-Signal Generator tuned to crystal frequency
-selectivity switch in IF Sharp position-now, adjust
screw on top of T4, after loosening lock nut, to zero best.
(See Fig. 8)
(3) Noise Limiter and A VC
A~plifier
Adjustment: Have
the Controls .set as before except that the A VC switch is
now in the ON position. Connect a high resistance type
.voltmeter across R49 which is connected between termi-
nal #5 of the 6L7 tube and cru;,ssis. Connect a 50,000
(P
ohm resistor across primary ofTS (Rec1and 'Blue leads). .
Set generator at 455
~c
as for IF alignment. Connect gen-
erat,?r to grid of 6AB7 tube (pin #4). RotateANL control
all the way to the right, or position
#9.
Adjust screws
on top-of T5 for maximum indication on DC meter coq-
n~ctea
across R47. Reconnect generator, as for IF align-
ment, to mixer grid of 6SA 7· tube .. RemQve 50,000 ohm
~sistor
which was inserted across primary of T5 during
alignment. Remove grid clip off top of 6L7 tube. With
generator set at 455 kc and ANL control at extreme right
adjust wave trap trimmerC55 for
mi~imum
signal
~s
indicated on output meter. (See Fig. 8 and Fig. 1:4 for
location of adjustments).
With generator connected to 6SA7 mixer grid as above,
replace 6L7 grid and turn ANL control to extreme left
until switch clicks. Connect high resistance DC meter
across 6BS diode filter condenser C64. Adjust, screw
0.1'1
top of T6 for maximum indication on DC meter across
C64.
(4) For RF and oscillator adjustment location and align-
ment procedure see Fig., 12.
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