Simpson Electric 479 User manual

OPERATOR’S
MANUAL
MODEL 479
FM-TV
SIGNAL
GENERATOR
SIMPSON
ELECTRIC
COMPANY
5200 W. ICinzie
St.,
Chicago 44, Illinois,
ES
9-1121
In Canadz.
Bach-Simpson. Ltd., London,
Ontario
'
Simpson
Electrk Co.,
Chkogo
44,
IIInos
1

A. M.
GENERATOR
400
r,
AUDIO
GENERATOR
F.M.
GENERATOR
CRYSTAL
CALLBRATOR
FIG.
1.
THE
MODEL
479
TV-FM
SIGNAL
GENERATOR
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MODEL
.479 + TV -FM
SIGNAL GEHERATOD
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MODEL 479
FM-TV
SIGNAL
GENERATOR
The
Simpson
Model 479
Signal Generator
has been designed carefully
to
supply all
the
necessary
signal sources
for the
proper
alignment
and
servicing
of TV
and
FM
receivers. For your
convenience,
markings on the
FM Generator
tuning dial allow you
to tune
it
according
to the frequency
which you
require, or
according
to television
chan
nel
number
for RF
signals
through
both
VHF
and
UHF
ranges.
There are two
separate
tunable oscillator
sections. Each oscillator
section
is
pro
vided
with
a
large,
precision
vernier dial
having
a
20:1
knob-to-pointer
ratio and
a
1000
division
logging
scale.
They are easy
to read and
easy to set to any exact
fre
quency within the
range of the
generator.
Everything
possible has
been done to
make
the
Model
479
the most
accurate,
flex
ible and
convenient
instrument
available. Each part
of this
instrument has
been
con
sidered
carefully
for long life and
stability. Many of the
vital
components are manu
factured under
rigid supervision
within our own
plants
in order
to insure lasting accur
acy
and many
years
of uninterrupted
service.
DESCRIPTION
The
Model 479
is
arranged
in
two
major sections as shown in
figure
1. The left
hand section contains
a
crystal
calibrator, a 400 cycle audio oscillator, and
a three-
range r-f generator
which can be amplitude modulated
with
the
output of the
400
cycle
oscillator.
The
desired
type
of signal is selected
by the SIGNAL
switch left. The SIGNAL
switch
has
five
positions, named OFF,
tJNMOD. R.F., CAL.,
MOD.
R.F.,
and AUDIO.
When the switch is in the
OFF position, the entire
A.M. Generator is
inoperative. When the
switch is in
the
UNMOD. R.F. position, anunmodulated r-f
signal
is
available through the
OUTPUT
jack
and
cable. The amplitude
is
controlled with the SIGNAL
ATTENUATORS,
with
both
fine
and coarse adjustments
center and right.
When the switch is in the
CAL.
position, the
output of a
5.0
mc. crystal oscillator is mixed with the
output of
the
R.F.
Generator
to produce a
"beat" according
to the
information in
table
1. The
beat
pattern
can
be observed on
an
oscilloscope
connected with
the VERT.
AMPL.
and
HORIZ. AMPL. cables.
By
using
table 1 and the
oscilloscope,anyfrequency
within the
range
of the instrument
can be produced quickly
and
precisely.
When the switch is in
the MOD.
R. F.
position, the r-f signal is
amplitude
modulated
30% with
a
400 cycle
audio
frequency and the
modulated
signal is available through
the OUTPUT
jack
and
cable.
The amplitude
is controlled
by the
SIGNAL ATTENUATORS.
When the
switch
is
in the AUDIO position, a
400
cycle signal
is
available through
the OUTPUT jack
and
cable. The
amplitude
is controlled by
the
SIGNAL
ATTENUATORS.
A
potentiometer
and a five-position
switch
together comprise
the SIGNAL ATTEN
UATORS.
The
switch, at the
right,
is the coarse amplitude selector
for
the
output
of
the
a-rn
generator,
and the potentiometer acts as
a
fine
adjustment
on amplitude.
The
A.M. GENERATOR RANGE switch, located just
below the center
of the dial,
selects
each
of the
three bands
of
radio
frequencies.
The
tuning knob
varies
the fre
quency
throughout each
band.
Band
A.
Fundamental
3.3
to 7.8 mc.
Second harmonic
6.6
to
15.6
mc.
Band
B.
Fundamental
15
to
38
mc.
Second harmonic
30
to
76
mc.
Band C. Fundamental
75
to
125
mc.
Second
harmonic
150
to 250
mc.
-3-

The POWER
switch lower enter controls
the
power
input to both sections of the
Model
479.
When the
switch is in
the OFF position the
entire instrument
is
turned off.
In the
STAND BY position,
all the tube
filaments are
turned
on
but
no plate voltage is
applied. In the OPERATE
position,
plate
voltage is applied.
The green light
is on
for
both
STAND BY and
OPERATE positions of
the
switch, and
the red
light
is on
for
the
OPERATE
position only.
In the center of
the Model
479
there are three
jacks which
are labelled, from
top
to bottom, HORIZ.
AMPL., VERT. AMPL.,
and
SIGNAL INPUT. A cable from the
HORIZ.
AMPL. jack
should be connected
to
the horizontal
input terminal with the red
insulated clip and
ground
with
the black
insulated
clip
of the
oscilloscope used in
con
junction
with the
Model
479.
Set the function switch of
the oscilloscope to utilize this
signal
for the
horizontal
sweep. The switch position
will usually be named
"horizontal
amplifier or
"horizontal
input" on
the oscilloscope.
This connection is
important be
cause it offers
the operator his
most
convenient
source of
60
cycle sine wave sweep
voltage
which
may be
phase adjusted relative to the f-rn sweep
voltage with the
PHASING
control
on the
Model
479.
There
is
more information on
this in
the discussion of the
PHASING control.
A cable from the
VERT.
AMPL. is
used
to
connect the source
of the
response pattern to the
vertical input terminal with the
red insulated clip
and ground
with the
black insulated
clip of the
oscilloscope.
A cable from the SIGNAL
INPUT
jack is used to
connect the
signal
output of the amplifier
under test
back
into
the
Model
479.
This
signal
will be fed through the SIGNAL switchto the
VERT.AMPL. jack
when
the switch is in the
OFF,
UNMOD.
R.F.,
MOD.
R.F., or
AUDIO position.
The right
hand
section of the Model
479
contains a
frequency modulated signal gen-
erator,a 140
rnc.fixedfrequencyoscillator,a mixer,
and phasing and blanking circuits.
The
output
of the f-rn
signal generator is
connected
through an attenuator to the OUTPUT
jack.
The OUTPUT
jack serves both the a-mandthe f-rn
signal generators
so that
only
one
connection
need be made to the input of
the
receiver.
The F.M.
GENERATOR
RANGE switch below
the center
of
the
dial has
three posi
tions.
In
the
OFF
position,
the f-rn
generator section of the
Model
479
is
inoperative.
In
the
A
position,
both
the
140
mc.
fixed frequency oscillator
and
the tunable f-rn oscil
lator are
operating;
one output
frequency from
the mixer
is
the difference between these
two
frequencies.
The
fundamental
range of
the
beat frequencies
is.2
to
120 mc. The
locations
for RF
signals
for television
channels
2
through
6
are marked in
areas
be
low
the
corresponding
frequencies. In
the
B
position, the switch
turns
off the
140
mc.
fixed
frequency oscillator, and
the output
from the variable frequency oscillator
is
available
at
the
output.
The fundamental
range
of the
B band
is
140
to
260
mc, The
locations
for RF
signals
for channels
7
through
13,
which
use fundamentals of the
B
band, are
marked in
areas
below
the
corresponding frequencies. The
locations
of B
band
frequencies
which
will
have
harmonics required
for
RF signals
for
channels
14
through 83
are marked
ingroups
above
theB
band.
Channels
14
through
21
use
second
.jiarmonics,22
through65use third
harmonics,
and66
through83
use fourth
harmonics.
The tuning
knob
in
the dial
serves to
select
any frequency within
the
range
indicated on
the
arcs of
the
CENTER
FREQUENCY dial.
The F. M.
ATTENUATORS are two
controls which act
as
coarse and fine
adjust
ment.
A
5-position
switch provides
coarse control on
attenuation
and a continuously
variable potentiometer
provides
the fine control.
The
F.M. SWEEP control regulates
the
amount
of frequency variation
due to
modulation. The center frequency of the
fundamental
can be swept
through
a
band
width
of zero to
15
megacycles. Harmonics can be
swept through multiples
of
this
band
width, corresponding to the harmonic order. The
rate at which center frequen
cies
are swept
through any selected range
and back is the modulation frequency
of
60
cycles.

The PHASING
control
is
a phase adjuster on the 60 cycle sine wave
signal
furnished
to
the
HORIZ. AMPL.
jack.
It is to
be used
to
adjust the phase
relations between
the
oscilloscope
sweep
and
the 60 cycle sweep modulationon
the
carrier.
With the
PHASING
controlitis
possible
to superimposethe response pattern on the
forward trace
over
the
pattern
on the
return
trace.
The BLANKING
control has
a
potentiometer and
a
switch
on the same
shaft. The
switch
is
actuated
at the
full counter-clockwise knob position.
When the knob
is in
the
OFF position, no
blanking occurs
and
the F.M. Generator oscillates
continuously,
When
the knob
is
rotated
towardits numbered range,the switch actuates and
applies a
60 cycle
voltage to the
f-rn
oscillator
grid
to
block out
oscillations
during its
negative half
cycles.
Turning
the
BLANKING
control through its
numbered
range changes
the phasing
of
the
blocking
voltage
with respect to
the horizontal
sweep to the oscilloscope. Thus
either
the forward or the
return trace can coincide with the period of oscillation
and the alter
nate trace can coincide
with the
time
during which
the
oscillator
is turned off.
On the
oscilloscope,
the operator
will
see a single response curve with
a
base
line
through it.
Four cables are furnished
for connecting the Model
479
to a receiver
and to
an
os
cilloscope. One
cable fits
in
the
OUTPUT
jack and has
a termination
box at
the other
end which may be
adapted
quickly
to the receiver input impedance
with
an optional
2000
rnmf capacitor in
series
for use on circuits having
a
d-c component. Most
receiver
inputs can be
matched
without using
any
external resistors or capacitors.
See table 2
and figure 14. The
other
three cables are identical
and
are to be used
in the HORIZ.
AMPL., VERT.
AMPL.,
AND SIGNAL INPUT jacks. A pair
of
clips
at
the
other end of
each cable
are
to
be used
for receiver output and oscilloscope connections.
The red
insulated clips connect the
"hot
leads
and the
black insulated clips
are for ground con
nections.
During normal
alignment procedure,
the signal
is
sent out
of
the
OUTPUT jack, to
the receiveir under
test,
returned to the Model
47.9
through
the SIGNAL
INPUT
jack,
through
the SIGNAL
switch many position except CAL.,
and out the VERT.
AMPL.
jack
to the
oscilloscope.
This
arrangementwas
designed
to
simplifythe alignment operation
byinternalswitchingof
the
oscilloscope input.
Whenthe SIGNAL SWITCH
is
in
the
CAL.
position,
the
signal fed to
the VERT.
AMPL. jack is
the
audio beat frequency
produced
by
the a-m
generator and
the crystal calibrator near any
of the calibration
points
listed
4’r,
+h1’
CALIBRATION
PROCEDURE
FOR DETERMINING
TUNABLE
FREQUENCIES
WITH CRYSTAL
ACCURACY
The Model
479 has
two
precision
vernier dials; one
is used for the
a-rn generator
and the other
for the
f-rn
generator. The a-mgenerator
can be used as
a
marker gen
erator for both FM
and TV
alignment. It needs to be
extremely
accurate to
adjust
FM
and TV receivers
properly. The
basic
accuracy is
better than 1% output frequency
against
dial indications,
but it
needs
to
be even
more
accurate for alignment. For
this
reason, the Model 479
is
provided
with a crystal
oscillator
standard having an accuracy
of .05%
or
better,
It
is
by
use of this
standard
and
the logging scale of the a-rn
gen
erator that
frequencies
with crystal
accuracy may be
established at any point in
the
range of
the
a-rn
generator.
To prepare
the
Model
479
for calibration, turn
the POWER
switch
to
OPERATE;
SIGNAL switch to
CAL.;
SIGNAL
ATTENUATORS
to a
low
setting; and the
A.M.
GEN
ERATOR RANGE
switch to
A,
B, or
C
depending on
the
frequency
to be
established.
Connect the
VERT.
AMPL.
cable
to the vertical input
of
the
oscilloscope.
Connect
the
HORIZ. AMPL.
cable
to
the
horizontal
input
of
the
oscilloscope if
a60 cycle sine
wave
sweep
is
desired
calibration
beats can
be observed
with either
a
60 cycle
sweep or
linear sweep in
the
osci]oscope.
With
horizontal
deflection on the oscilloscope
due
to
-5-

either
the
internal sweep
or the
60
cycle sine wave
sweep, advance the vertical
arnpli
fier gain
of the oscilloscope
and slowly rotate the
a-rn generator tuning knob
while
observing
the
oscilloscope
screen. At
various tuning
points a
pattern will appear on
the
oscilloscope
screen.
Rotate
the dial slowly through
the
area in which
a pattern
can
be seen.
First
a
high
frequency appears, then as
the
knob is
rotated slowly,
note that
the
frequency
reduces
to
zero,thenincreasesto a high
frequencyagain
and disappears.
The
patterns are the
results of
beat
frequencies developed
between the a-rn oscillator
and the
5.0
mc
crystal
oscillator.
The
point at
which
the pattern reduces to zero
frequency
is known as zero
beat and
is
the point at
which
the
two oscillators are in
step.
The
zero beat point is identified
easily
by the fact
that
the slightest
movement of
the
dial in
either direction will cause
the
pattern to
increase
in height
and in
frequency.
At zero beat the pattern is, essen
tially, a straight
line.
At the
higher
frequencies it is
sometimes
difficult to bring
the
pattern down to exact
zero beat, but this is not important
so long as it
is
brought down
to
within two or
three
hundred cycles. This shows
three
to
five cycles on a 60 cycle
sweep.
Note
that some
points
on
the
dial will produce much
larger patterns
than others.
This is due to
the
order
of
harmonics of the two
oscillators
producing
the beat pattern.
The lowei harmonics
result in a stronger beat pattern.
Some of the
weaker
patterns
may require a
higher
setting of the vertical gain control
of
the
oscilloscope.
TabLe
1
has
been developed to assist
the
operator in
identifying
the
frequencies
where beat
patterns occur and the oscillator harmonics which produce them.
The
frequencies preceded
by an asterisk
4
will
produce the
stronger patterns
and should
be used wherever
possible.
FIG.
2.
THE
MODEL 479
AM-FM LOGGING DIAL
Figure
2 is an illustration of the
logging arcs as they
are
used
in
both
a-rn
and
f-rn generator
dials. The upper arc of
each
dial is divided
into 10
equal divisions
marked from
0 to
100.
On the knob shaft
is
another dial
marked
in 100 equal divisions.
The gear. ratio
between the knob shaft
and the
pointer is such that one
revolution
of
the
knob shaft moves
the pointer through
one
of
its ten
divisions. Thus each division of the
logging scale is
effectively
divided into 100 parts and the
entire arc
into 1000
parts.
The minor
divisions may be divided
visually for further
increasing
the number
of
logging
points and
the
resulting
accuracy of calibration
information. For example,
the
reading
on the logging
scale in figure
2
is 22.5.
The main
pointer shows that
the
setting is 20
plus some
additional amount, and
the
dial
on the
knob
shaft shows
that the additional
amount is
2.5. If the knob
were
turned slightly
counterclockwise
so
the
dial
setting
were half way
between 2.5 and 2.6, it could be read as
2.55 and the
indicated
setting
would
be 22.55
divisions.
Take
advantage
of
the visual
division
of these
marked
points
and effectively
increase the
accuracy
to 2000 or more
scale
divisions.
-6-

TABLE
I
- CRYSTAL CALIBRATING
POINTS
BAND
A
BAND B
BAND
C
2ND
VAR. XTL.
2ND
VAR.
XTL.
2ND VAR. XTL.
FUNDAMENTAL HARMONIC
OSC.
OSC.
FUNDAMENTAL HARMONIC
OSC.
OSC.
FUNDAMENTAL HARMONIC OSC. OSC.
MEDACYCLES
MEGACYCLES
HARM. HARM. MEGACYCLES
MEGACYCLES
HARM.
HARM.
MEGACYCLES MEGACYCLES
HARM. HARM.
*333 *7
3
2
*1500
‘30.00
1
3
‘70.0
‘140
1
14
3.46 6.92
13
9 15.83
31.66
6
19
72.5 145 2 29
3.50 7.00
10 7
16.00
32.00 5 16
‘750
‘150
1
15
3.57 7.14
7
5
16.25
32.50 4
13
77.5 155 2 31
3.64
7.28
11
8 ‘16.67
‘33.34 3
10
‘80.0
‘160 1
16
*375
*7.50
4
3 17.00 34.00 5
17
82.5 165 2 33
3.89 7.78
9 7 ‘17.50 ‘35.00
2 7
‘85.0 ‘170
1
17
‘4.00 ‘8.00
5
4
18.00
36.00 5
18
87.5
175
2
35
4.09 8.18 11 9 ‘18.33 ‘36.66
3
11
‘90.0 ‘180
1
18
*4
17
‘8.34 65
18.75 37.50
4
15 92.5
185
2
37
4.29
8.58
7
6
19.00 38.00 5
19 ‘95.0 ‘190
1
19
4.38 8.76
87
‘20.00 ‘40.00 1 4 97.5 195 2
39
‘4.44
‘8.88
9 8
21.00
42.00 5
21 ‘100.0
‘200
1
20
4.50 9.00 10
9
21.25
42.50
4
17
102.5
205
2
41
4.55 9.10 11
10
‘21.67 ‘43.34
3
13 ‘105.0
‘210
1
21
4.58 9.17 12 11
22.00 44.00 5
22
107,5
215 2 43
‘5.00 ‘10.00
11
‘22.50
‘45.00 2 9
‘110.0 ‘220
1
22
5.63
11.26
89
23.00 46.00 5
23 112.5 225
2
45
‘5.71 ‘11.42 7
8
‘23,33
‘46.66
3 14 ‘115.0
‘230
1
23
5.83 11.66 6 7
23.75 47.50
4
19
117.5
235
2
47
6.00
12.00
5 6
24.00
48.00
5
24
‘120.0 ‘240
1
24
‘6.25 ‘12.50 4
S
‘25.00
‘50.00
1
5
122.5 245 2 49
6.43
12.86
7
9 26.25
52.50 4 21
‘125.0 ‘250
1
25
‘6.67
‘13.34
3 4
26.67 53.34
3
16
6.87 13.74 8 11
‘27.50 ‘55.00 2 11
‘7.00
‘14.00
5 7
28.33
56.66 3
17
7.14 14.28
7
10
28.75 57.50 4
23
7.22
14.44 9
13
‘30.00 ‘60.00
1 6
‘7.50
‘15.00
2 3 31.67
63.34 3 19
7.72
15.44 11
17 ‘32.50
33.33
‘35.00
36.67
‘37.50
‘65.00
66.66
‘70.00
73.34
‘75.00
2
3
1
3
2
13
20
7
22
15
ASTEHISK ‘ INDICATES
ThE SThONGEB
CALIBRATION
POINTS.

DETERMINING
AN
EXACT
FREQUENCY
There
are
two
methods
by
which a
given
frequency
setting may
be
obtained. They
are
somewhat
similar
but one
is simpler
while the
other
yields more accurate
resuits.
The first method
is
the
simpler and,
with practice,
can
produce acceptable
results
for most
purposes.
The
process
consists of
first
determining
the number of
logging
scale
divisions
which
correspond
to
a
one
megacycle
frequency difference
which in-
cludes,
the desired
frequency;
second,
mathematically
figuring the number
of logging
scale divisions
the
desired
frequency
is away from
a
crystal check point see
table
1;
third, turning to
the
crystal
point and
observing its
logging
scale reading; and fourth,
adding
or subtracting
the determined
number
of
scale divisions to
or from
the
reading
at the
crystal
check point.
When
the logging scale
is
set to the
reading obtained in the
fourth
step, the
oscillator
will be tuned to
the desired
frequency.
A
step-by-step
example
of
the first
method
follows.
Assume that a
frequency
of
20.75
mc. is
desired
in the A.M. Generator.
Note
that
table
1 shows a strong cali
bration check point
at
20 mc. Set the A.M.
GENERATOR
RANGE
switch to
B,
the
SIGNAL
switch
to
CAL.,
and the
SIGNAL ATTENUATORS
low to see the zero beat in
dications on an
oscilloscope
with the VERT. AMPL.
and
HORIZ.
AMPL. cables con
nected. Have the
POWER
switch in
either STAND
BY or OPERATE position
for
at least
15 minutes before
beginning
the calibration
to
allow
the Model
479 to
warm
up,
and set
it in the OPERATE
position to
calibrate.
1. Observe the tuning
arc of range Bfrom
apositiondirectly in front
of the
pointer
to avoid
parallax
error and set the
pointer over the
20 megacycle mark
on the
dial..
Record the logging
scale reading
for this setting. Ona sample unit the setting was 36.0
use your readings, since there
will be variation from
one unit
to another which does not
affect the accuracy in
any way. Set the pointer
exactly over
the 21 megacycle
mark on
the dial.
Again record
the logging scale reading.
The sample
unit read
40.45
for
this
setting.
Subtract
the
first
reading
from the second to obtain the number
of
scale
div
isions which correspond
to one megacycle. 40.45 - 36.0
is 4.45
divisions.
2.
Determine
the frequency difference, in megacycles, between the desired
fre
quency and a check point
table I; then
multiply
this difference
by
the
result of step i
above. In the example, the desired frequency of
20.75
mc. is .75 mc. away from the
strong calibration check
point
at 20 mc. The result
of step 1 shows
thatin this
area
of
the
sample
unit, a
change of
4.45 scale
divisions
corresponds
to a change of one
mega
cycle.
Multiply
.75 x 4.45
to get
3.33
divisions.
3.
With the aid of the oscilloscope, tune the
generator to
its zero beat position
for
the chosen calibration check point
and record
the logging scale setting for
this
position.
In the
example, the sample
unit was
tuned to
20
megacycles and the logging scale read
36.2 divisions.
4.
Add
or
subtract
the, results
of
steps
2
and 3. Add
if
the check
point frequency is
lower
than the
desired frequency, or
subtractif the check point frequency
is
the
higher.
This
sum or difference is
the
logging scale setting
to
use for the desired
frequency. In
the
example,
add
because the check
point is below
20.75
mc.
3.33
to 36.2
to
obtain
39.53
divisions.
Note
that the logging
scale readings
are for
a
sample
unit only.
Do not
use
these
readings.
Obtain
the
logging scale readings
for your Model
479
and
use
them in a
sim
ilar way.
Although you
will be using
some
frequency settings
repeatedly,
do
not
rely
on the
stability
of the
instrumentover long
periods of time; the
components
are subject
to
normal
deterioration
and will cause slight
changes of
logging scale
settings
in
time.
-8-

The second method
is different from
the first
only in the fact
that
two
crystal
check
point settings
are used in place of two
dial
markings. First,
determine the number
of
logging
scale divisions
which correspond
to
the frequency difference between
two crystal
check points surrounding
the desired frequency;
second, mathematically figure the
num
ber
of
logging scale divisions the desired frequency is away
from
one of the check
point frequencies; third,
add
or subtract
the
determined number
of
scale divisions to
or
from the reading atthe
crystal check point. Add
if the lower check
point is the reference,
or subtract if the
higher check
point is
the reference. When the
logging scale is
set to
the reading
obtained in the
third step, the oscillator will be tuned to
the
desired frequency.
The
accuracy obtained
by this
method is better than 0.1%
A
step-by-step
example of the second method follows. Again,
assume that a
frequency
of
20.75
mc. is desired in the
A.M. Generator.
Note that the
two
nearest strong crystal
check
points
are 20.0 and 21.67 mc. table 1.
There
are weak
check
points at
21.0
and
21.25
rnc.,but these
are not recommended
because
they are
close
together and difficult
to identify. Set the
A.M,
GENERATOR RANGE switch
to
B,
the
SIGNAL switch to GAL.,
and the SIGNAL ATTENUATORS low
to
see the
zerobeatindications
onan oscilloscope
with the VERT. AMPL.
and HORIZ. AMPL.
cables connected.
Have the
POWER switch
in either
STAND
BY
or
OPERATE
position
for
at
least 15
minutes before beginning
the
calibration
to
allow the Model
479 to
warm up, and
set it in the
OPERATE position
to
calibrate.
1.
With the aid
oftheoscilloscope,tunetheA.M.
GENERATOR around the 20 mega
cycle
point for the zero beat indication. Record the logging
scale setting for
the zero
beat position. On the sample unit, the
reading was
36.2
divisions use the
reading on
your own
Model
479; this is for an example only. Retune
the A.M.
Generator around
the 21.67
mc.
point for the zero beat indication. Record
the
logging scale
setting
for
this zero beat position. On the sample unit,
the
reading was 43.3
divisions. Subtract
the first reading fromthe second for the number of logging scale
divisions between the
check point
frequencies.
For
the example,
43.3-36.2
is 7.1 divisions.
2.
Determine
the frequency
difference between the
desired
frequency
and
either
check point frequency.
In
the example, the desired frequency
20.75 mc.
is
.75
mc.
above
the
lower check point
and
is
.92
mc.
below the upper check
point.
Next
find the
frequency difference
between
the two check points. In the
example this is
1.67
mega
cycles.
By
ratio
and
proportion, the frequency deviations can
be translated into scale
divisions for the
logging scale;
F1
= or P1 D2
where
D1 logging scale
divisions between one
check
point
and
the
desired
frequency,
D2 logging scale
divisions between tyvo
check points,
F1
frequency difference
between the
same
check point see D1
above and the
desired frequency,
and
F2
frequency difference between
the two
check
points.
-9-

In the example, using
the
.75
mc.
deviation
from 20 megacycles,
7.l 3.19
divisions.
3.
If the lower
check
point was
used to determine
Di
in
step
2,
add D1
to the log
ging scale setting
for
this check point;
or
if
the higher checkpoint
was
used to determine
Di
in step
2, subtract
Dl
fromthe
logging scale settingfor this check point. The result
will
be
the
logging
scale setting for the desired
frequency.
In the example,
add
3.19
to
36.2
to get
39.39
divisions
which is a
very
accurate
setting to obtain 20.75
mc. on
the
sample unit.
Use table 3 at the
back of the manual
to
record the
settings
for the
various
fre
quencies after they
have been
determined.
This will save
timewhenever
the use of
any
frequency is
repeated. Note
that four columns
apply to
each frequency
listed: the
first
column will contain
the desired frequency; the second column
will have
the log scale
setting
which has
been determined
for
the desired frequency;
the
third column
will
have
the
nearest
crystal check point frequency; and the
fourth column will have
the
log
scale setting of the
crystal check
point.
To use, after it
has once been filled infor any
given frequency, zero
beat the crystal check
point
frequency and compare the
reading
of the
logging
scale
against
the
listed setting
of the
fourth column. If the readings
are
identical,
tune to
the
logging
scale setting
of the desired
frequency listed in the second
column and you
will have
tuned the oscillator to
the
desired
frequency. However,
if
there is
a
difference
between
the
log scale setting for
zero beat at the check point and
the listed setting in the
fourth column, it indicates that the
components of
the
oscillator
have changed, and
the logging
scale settings
need
correction.
If the
log
scale
setting
for
the crystal
check
point has changed
up or
down one,
two,or three divisions, the set
ting for
the
desired
frequency
has
changed the
samenumberof divisions.
in
the
same
direction
so add
or
subtract
the change to or from the
column 2 listing to provide a
corrected setting.
There is enough space in both tbesecondandfourth
columnsto keep
a record of any
changes
over a long period of time.
For greater
accuracy,
if the
scale
settings change
more
than five divisions, recalculate the
column
2
listing rather than
add or subtract
divisions.
PRINCIPLES OF VISUAL ALIGNMENT
The visual method
of adjusting resonant
circuits
has been developed in order to el
iminate the tedious
procedure of point to point measurements which
would
otherwise
be
necessary
to determine the
response
characteristics
ofa tuned
circuit or
a number
of tuned
circuits such as used
in radio
and televisions
receivers.
Referring to figure
3
it is obvious that a response
curve can be traced by applying
a signal
of fixed amplitude
to the input
of
the circuit and measuring the output voltage
as
the
frequency
of the generator
is varied. This,
ofcourse,requiresnumerousrreas
urements
and is
impractical for the purpose of circuit adjustment.
The visual
align
ment
procedure accomplishes
the same result
but is instantaneous.
Here
the
gener
ator frequency
is
varied
above
and
below
circuit resonance at a fixed
rate.
-10-

FREQUENCY
IN
MEACYCLE
FIG. 3.
GRAPHIC
REPRESENTATION
OF
A
RESPONSE
CURVE
The
vertical amplifier
of an
oscilloscope
is connected across the
output of the
cir
cuit in order to
indicate
the instantaneous voltage appearing at
various points along
the curve
and the oscilloscope
sweep
is
synchronized with the generator frequency
dev
iation
in such
a
manner that
the entire
resonant characteristic of the circuit
is
regist
ered on the oscilloscope
screen.
By this method
the
operator
can
see
instantly
the effects of
the
adjustments
as he
proceeds with the
alignment.
This
type
of alignment
is of particular value in television receivers because of the
wide band
characteristics
necessary
for
satisfactory
reception.
ALIGNMENT
PROCEDURE
It would
be impossible to
cover all of
the various
alignment
procedures in
this man
ual since
each
receiver manufacturer determines the sequence
of adjustment
best suited
to his particular product.
Follow the receiver
manufacturer’s
service
instructions when
making
tests and
adjustments
on
a television
receiver.
The following
paragraphs
will
explain
the
various
steps
in the alignment
of a
typical
receiver andmaybeusedasa guide for
adaptingtheModel479
and an associated oscill
oscope
to any
manufacturer’s specific
instruction.
The general procedure is as follows:
1, Connect
the Model
479
to a 110 volt
60 cycle power
outlet.
2.
Turn
the POWER switch to the
OPERATE position.
3.
Connect the
receiver to
a power
outlet
and turn it
on. Adjust
the contrast
control to
approximately
3/4 of maximum.
Some
receivers
require a battery
bias to
simulate normal
AGG.
4.
Allow the
receiver
and the Model
479
to
warm
up for
about 15
minutes
be
fore
attempting
to
make any adjustments.
The
Model
479
will
not require additional
warm up time
if
the
POWER switch has been
left in
the
STAND
BY position.
-11-

5. Connect
the HORIZ.
AMPL. cable
to
the
horizontal input terminals of the
oscilloscope,
and the VERT. AMPLJ. cable to
the
vertical
amplifier input.
6. Set
the oscilloscope
switches and controls
as
follows: vertical sensitivity
high, vertical gain at 0,
horizontal gain
as
required to
obtain
a
convenient horizontal
deflection
on the
cathode
ray
tube,
and
function
switch
to the position which will
connect
the
horizontal
input through
the horizontal amplifier.
7. Advance
the
oscilloscope intensity control
and focus control
until
a thin
bright horizontal
line is seen on the cathode ray tube.
Center
the trace
horizontally and
vertically.
8. On
the Model
479,
set
the controls as
follows:
F.M. GENERATOR
RANGE switchatOFF: A.M.
GENERATOR RANGE
switch to
B;
SIGNAL
switch
to
GAL., and
SIGNAL ATTENUATORS
low.
9.
Advance the
oscilloscope vertical gain control
to about
mid
rotation
and re
adjust as
desired
during
the following steps.
10.
Refer
to
the receiver manufacturer’s literature
for the frequencies
which
will
be
required
during
the adjustment. Determine the
logging scale settings
to
tune these
frequencies; use the
instructions givenunder CALIBRATION
PROCEDURE
in this man
ual. The frequencies
specified for this example of
a typical circuit are;
19.75,
21.25,
21.8,
22,3,
23.4, 25.2,
25.3,
and 27.25 mc, Seefigure4.
Anewtendencyamong
receiver
manufacturers
is to
use an intermediate
frequency
centered around 45
mc.
ll.
Set the
OUTPUT
cable
termination for
75 ohms by jumpering terminals 6-
7-8-9-5
and terminals
2-3-4. Open termination may
be preferred. See
table 2
for
instructions.
Connect the alligator clip on the end
of the
probe
to point "F
" of
figure
4. Connect the ground lead of the probe
to
the
receiver chassis. Note
that
the
alligator
clip
and ground
lead
may
provide too much
inductance
for use at 45 mc
See the
special instructions
on
page 24. Connect the SIGNAL
INPUT cable to
point A
"of
figure
4.
fcowvrg
AUDIOI ‘ -
DT
12.
Rotate
the SIGNAL
switch
to MOD. R.F. and
adjust
the SIGNAL
ATTEN
UATORS
and the oscilloscope
vertical gain control
until a good size
Lissajou
pattern is
seen
on the
oscilloscope.
The
SIGNAL
ATTENUATORS
should be operated at
the
lowest
setting which will give a
good oscilloscope pattern.
13. SettheA. M.
GENERATOR logging scale to
the point recorded for
19.75
meg
acycles and
adjust
L7
point
"1
"of figure
4
for
minimum
patternheight.
If the
pattern
disappears
completely,
increase the attenuator setting until
the exact
minimum
point can
be observed.
14.
Set the logging
scale at the point recorded for 21.25
mc.
and adjust the
sound
FIGURE. 4. TYPICAL TV VIDEO
IF SYSTEM
-12-

takeoff
trap L3
point 2 for
a
minimum
indication.
15.
Leave the Model
479
set
at 21.25
mc. and
adjust the
accompanying
sound
trap
L9
point
3
for a
minimum
indication.
16. Set the logging
scale
to
the
point
recordedfor 27.25
mc.
and
adjust
the ad
jacent
channel sound trap L5
point 4
for a
minimum indication.
This
completes
the
trap
adjustments.
17.
Set the logging
scale at the
point
recorded for 21.8
mc.
and
adjust the
con
verter
output LZ point
5
for
a
MAXIMUM
indication. If the
pattern
becomes
too
large,
reduce
the SIGNAL ATTENUATORS.
18.
Set the logging scale
to the point
recorded for 25.3
mc. and
adjust
the
first
IF
L4
point 6
for
maximum.
19.
Set the
logging scale to
the
point recorded
for 22.3
mc. and
aojust
the
second
IF L6 point
7
for
maximum.
20.
Set
the logging scale to the
point recorded for 25.2
mc. and
adjust the
third
IF
L8
point
8
for maximum.
21.
Set the logging scale to
the point
recorded for
23.4
mc.
and
adjust
the third
IF
Lii point
9
for
maximum.
22.
If coils L2,
L4, and L6
have required appreciable
adjustment, the
associated
traps,
L3,
L5, and
L7
should be
rechecked
as
explained
in steps
13, 14,
and 16.
23. Occasionally a
receiver will
have a tendency to oscillate
during
alignment.
Usually
this is
caused bytwo or
more transformers
being tuned
to the same
frequency.
Such oscillationwill be
identified by.a
suddenhigh deflectiononthe CRT and
a scrambled
patternwhich cannot be
controlled
bythe attenuators. When
this
occurs, the
best remedy
is
to shunt points C,
D, E, and F with .001
mfd
capacitors. Connect
the Model
479
OUTPUT cable to
point
B
and adjust
Lii.
Remove
the capacitor at
point C and connect
the OUTPUT
CABLE to this point and adjust L8. Repeat this process
for each stage
back to point F, removing
the capacitor and
connecting the
OUTPUT
cable
to
points D,
E, and F. Adjust
L6, L4, and L2 for maximum indications. Some
manufacturers
rec
ommend the
latter, or backwards, sequence of adjustment. It makes
little difference
which
sequence
is used as
long
as each stage
is
adjusted carefully
to its assigned
fre
quency. This
completes
the i-f adjustments.
24.
Leave the
OUTPUT cable of
the
Model
479
connected
to
the
converter
grid
point
F
and
the
SIGNAL
INPUT cable connected across the
video detector load resis
tor
point A.
25.
Set the
SIGNAL switch
to the OFF position. Set the F.M. GENERATOR
RANGE
switch
to A, F. M. ATTENUATOR switch to MAX. and
potentiometer to
5,
PHASING
to
0, and
BLANKING
to OFF. Tune the F.M. GENERATOR
to approximately
23
mc. on range
A. A response
curve of the i-f
systemwill appear on the oscilloscope.
Adjust the
F.M.
Attenuators and
the
oscilloscope
vertical gain for a pattern
of cpnven
ient
height, keeping the
F. M. ATTENUATORS set as low as
possible. Adjust
the
PHASING control to superimpose the
two
traces.
Readjustthe
tuning
dial
until the pat
tern
is
centered
in the horizontal trace.
Readjust
the
F.M. SWEEP
control until the
patternincludesabouttwo-thirds
of the horizontal trace. Correct
the control
for super
imposed traces again. Rotate the
BLANKING
control
to produce a
base
line through
a
single
trace.
-13-

25,7
a5.75
FIG.
5.
PICTURE
IF
RESPONSE
- STAGGER
TUNED
26. Compare the
pattern with
the
one shown
in the
manufacturer’s instruc
tions.
Figure
5
shows
an
example of an
i-f response curve. If
the
system
has been
aligned properly, it
should resemble figure 5A.
27. Turn the
SIGNAL switch
to
UNMOD. R.F.
and set
the logging scale of the
A.M. Generator to the,
point for 22.3
mc.
A marker
should
appear
on
the pattern
as
shown
at
the
left
in figure 5
A, B, and
C. Adjust
the SIGNAL
ATTENUATORS and the
F.M.
ATTENUATORS for the
desired
balance of
signal strengths.
If the marker sig
nal is too strong, the curve
will be
distorted and it
will be difficult
to measure its exact
position
on the
pattern.
28. Set the logging scale to the point recorded
for 25.75
mc. and check the pos
ition of the marker. It should appear at
50% of
the
maximum pattern height. Setting
the marker frequency
to
the various
points
to
which the
system
was
adjusted
will in
dicate
the
part of’ the response curve
affected by each adjustment. Slight re-adjust
ment of the systemmay
be performed
at
these points
inorderto produce a satisfactory
response
curve.
However,
if considerable
adjustment
is necessary, the
entire
align
ment
procedure
should be repeated.
The foregoing paragraphs have dealt with the
alignment
of a
stagger
tuned
video
i-f
system. Another
system, known as
Band
Pass IF
and
used
in
many receivers,
requires
that the
entire
alignment
be
performed by use
of
the
F.M.
Generator.
In this type
of
receiver,
alignment
begins with the
last
i-f stage
and
proceeds
stage by stage back to
the converter. A set
of curves
is furnished
as
a
guide and it is only necessary to
follow
the sequence set up by the manufacturer’s
instructions, using his curves
to
indicate
the type ofresponse to be
expected. A
set of
sample curves appears
in
figure 6.
To adjust band pass
i-f, connectthe SIGNAL INPUT cable
to
the video detector
out
put and the OUTPUT
cable
to
the grid of
the
last i-f
amplifier. Set
the F.M.
GENER
ATOR RANGE switch
to
A and adjust the dial to
25
mc.
Set the F.M. ATTENUATORS
to
MAX.
and
10, and adjust PHASING and
BLANKING
controls and
the
associated os
cilloscope for a single image pattern with satisfactory ,height.
Set
the A.M.
GENER
ATOR
RANGE switch
to
B
and the SIGNAL switch to
CAL. Record
logging scale
read
ings
for the
recommended frequencies. In the
example,
these are 22.6, 22.75, 23.25,
23.75, 24.25, ‘24.6, 25.75,
26.6,
26.75,
27.0,
and 27.1 megcycles.
Set
the
SIGNAL
switchtoUNMOD,
R.F.
andthe logging
scale tothepoint
recorded for 27.1
rnegacycles.
Adjust the
SIGNAL ATTENUATORS to
the
lowest
setting which will
give
a
satisfactory
marker
on the
trace. Adjust the last i-f transformer
primary
and secondary for
a
single
peak
centered on the
27.1
mc. marker. Setthe A.M. Generatorloggingscaletothepos
ition
for 23.25
mc.
Adjustthe coupling condenser in the
last
i-f
transformer
for a
peak
centered at 2325
mc.
The curve
should now resemble figure
6A.
A
ftPRO?ERLY PLtGt4ED
MPROPERL’
ALIGNED
-14-

80
60
40
20
0
FIG. 6
VIDEO
ALIGNMENT CURVES - BAND
PASS TYPE
Move the OUTPUT cable
to the
grid of the preceding
stage.
Adjust the secondary
of this
i-f
transformer
fora peak at 23.75
mc. and the
primary
for a peak
at 26.75 mc.
There is
no
coupling
condenser adjustment for
this stage. The
response
curve should
now resemble
figure
6B.
Move the OUTPUT cable
to the next
preceding
stage.
Adjust the
primary
and
sec
ondary of the i-f transformer
for
a curve
having the
same shape and
relative
amplitude
as
that of
figure 6G.
Use the
marker at
the frequencies
indicated:
22.75,
24.25, 25.75,
and
27.0
mc.
Move
the
OUTPUT
cable to the
grid of the
converter.
Adjust
the
primary, secondary,
and
coupling
condenser of the
first i-f
transformer for a curve having
the same
shape
and
relative amplitude
as figure 6D. The check
points indicated for
marker use
are
22.6,
23.75, 24.6, and 26.6 megacycles.
Touch up adjustments
are
permissable to
improve the over-all
response curve.
Be
careful
to select
the
adjustment which affects
the partof the curve
which needs
correc
tion.
Figure
7
shows the
acceptable limits
of the over-all response
curve
with
the
amplitude at 24.0 mc.
for a
reference
point.
Conduct
the
alignment
to produce
a curve
which is
within these
tolerances.
The last five paragraphs
have outlined a
typical
process
for band pass i-f align
ment
only.
For
trap adjustments,
see steps
10 to 16 on page
12.
The trapadjustments
should
be made in the
order
recommended
by
the
receiver
manufacturer, with the
F.M.
GENERATOR
RANGE
switch
in the
OFF position
and the
SIGNAL
switch in the MOD.
R.F.
position.
Log the specified trap frequencies
in
advance.
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PICIURE i-F T0LRANCE
FIGURE 7.
RESPONSE
TOLERANCE
- BAND PASS
I-F
A
third
type of
circuit
uses
what
is
known as
intercarrier
i-f. The
principle
is
to provide
a
mixer and oscillator
to
produce an
intermediate
frequency,
and to
ampli
fy this
i-f
through
several
stages with
a
special
frequency response
characteristic;
the
band
pass
is
sufficient to include both
the
sound and the video center
frequencies,
and
the
response
maintains a desired
relative
amplitude between
the two center
frequencies.
Then
the beat
of
4.5 megacycles
between
the
two center frequencies
is
used to produce
a double
superheterodyne action
with
the
sound frequency
modulated
on the 4.5
mc.
carrier.
The sound
i-f
isuaiiy
one stage,
tuned to 4.5 mc.,
aLnpiifies the
sound
sig
nal
and
sends it to an f-rn
demodulator of any
type desired
by the
manufacturer.
It is
important
to follow
the alignment
data
indicated in the manufacturer’s
literature
be
cause
he has engineered
a
circuit
which
requires
specific
response
characteristics1
and no
generalization
could
represent the
large variety of possibilities.
The receiver
manufacturer’s literature
will
indicate
where the
test points
are
located, what
fre
quency
to use for each input,
what
adjustment can
be
made, and the resulting
response
wave
shape.
Set up
the Model
479
in
accordance with general instructions
and
use
an
oscilloscope
to
observe the results.
Use the
6O
sweep available
through the HORIZ.
AMPL.
cable
to
observe
the response
curve
in phase with the frequency
modulating
signal.
Sometimes
during alignment it is
desirable to have
two
markers at
different
fre
quencies
on the
response curve at the same
time.
A second signal
generator, unmod-
ulated, is necessary,
tunable
to the
frequency at which
the
marker is
desired. The
second generator can
be calibrated with
the accuracyof the Model
479 and
should be
as
stable as
possible.
To
calibrate
the second
generator,
set up the
Model
479
for its
normal
alignmentprocedure,
withthe OUTPUTfeedinginto a receiver and the receiver
output connected to
the
SIGNAL
INPUT cable.
Connect
the VERT. AMPL. and HORIZ.
AMPL.
cables to the
input terminals of
the associated
oscilloscope. Establish the
marker
on the
response curve
at
the frequency to which the second generator
will be
tuned.
Then couple
the second
signal
generator outputacross
the
termination box
or in
any
other
convenient
way to the receiver input. Sometimes the mere presence
of the
second generator on
the
test
bench will provide
sufficient
coupling without
any
direct
connections.
Now tune
the
second
signal
generator for a
beat indication with the marker
from
the
accurately
calibrated A.M.
Generator in the
Model
479.
Tune the
second
gen
erator
for
a
zero
beat indication
of
the two markers.
Then
change the
setting of the
Model
479
A.M.
Generator to
provide
the
second marker frequency. Both markers
will
show
on the
single
response curve.
F-M RECEIVER ALIGNMENT
The
order of f-rn
alignment usually
begins with the discriminator adjustment;
the
i-f
section is
next
and
the
r-f section
is last. If
the
receiver manufacturer
recommends
some
other sequence,
use
his
suggestions rather
than
these general instructions.
The
-16-

informationin
the
followingparagraphsisforthe
sound
section
of
a television
receiver,
but the same
principles
apply to
f-rn receivers
except
that
their intermediate
frequencies
are
usually_lower,
Figure 8
is
the
schematic
diagramofa
typical
sound i-f
system composed
of three
i-f amplifier
stages
andadiscriminator.
Thethird
i-f stage acts
asalimiter to reduce
the
effects
of
amplitude
modulation.
Usually the
alignment
will begin
at the discrim
inator and work
back, stage-by-tage,
to the
converter.
Proceed
as follows:
1. Connect
the
HORIZ.
AMPL.
cable and the
VERT.
AMPL. cable
to the input
terminals of the
associated
oscilloscope.
2. Connect
the
Model
479
OUTPUT
cable
between point "C
H
and
ground see
figure 8.
Use
any
desired
termination.
See table
2
for data on
the termination
box
connections.
Use
the
series
condenser
do not
jumper
terminals
1 and 6.
3. Connect
the
SIGNAL
INPUT
cable between
point
"A
" and ground
figure 8.
4. Set
the
F.M.
ATTENUATORS
to-
MAX.
and
10,
F.M.
SWEEP to 1,
PHASING
to
0, BLANKING
to
OFF,
F.M.
GENERATOR
RANGE to
B, and CENTER
FREQUENCY
dial pointer to
21.25 mc.
the
intermediate
frequency.
5. Set the
oscilloscope
controls
to
produce
a convenient
horizontal
trace cent
ered on the
face
of the
cathode
ray tube.
Set the
oscilloscope
function
control
so the
60
cycle sine
wave
voltage, fed
through the
HORIZ.
AMPL.
cable, is the
horizontal
deflect
ing signal.
6. Advance
the oscilloscope
vertical
gain until
the pattern is
one
to
two
inches
high. The
pattern
will be
two
S-shaped
response curves.
Adjust
the PHASING
control
to
bring the curves
in phase
as
shown in figure
9.
FIG. 9.
DISCRIMINATOR
RESPONSE
- IN
PHASE
- BLANKING OFF
7.
Adjust
the
F.M.
SWEEP
so the response
curve
covers
most of
the
trace as
shown in
figure
9.
Readjust
the
PHASING
control if the
traces
separate.
If
the
response
FIG. 8.
TYPICAL TV
SOUND IF
SYSTEM
DISCRIMINATOR
ALIGNMENT
-17-

curve
is not centered on the trac-e,
reset
the CENTER
FREQUENCY pointer to center
the
pattern.
Advance
the
BLANKING
control to produce
a
pattern
as shown
in
figure
10;
this
is
a
single curve with a
base
line
through it.
4
FIG.
10.
DISCRIMINATOR
RESPONSE
- BLANKING ADJUSTED
8. Reduce the
F.M.
ATTENUATORS
and advance the oscilloscope
vertical gain
for the
lowest attenuator setting
which
gives a satisfactory pattern.
9.
Set the
SIGNAL
switch
to CAL., A.M.
GENERATOR RANGE
to B,
SIGNAL
ATTENUATORS
low, and
adjustthe
frequency
to
exactly 21.25 mc.
see CALIBRATION
PROCEDURES
on
page 5
.
10.
Turn the SIGNAL SWITCH
to MOD.
R.E.
A pattern similar
to figure ii will
appear on
the oscilloscope
if the discriminator
secondary
is not
aligned
perfectly.
Re-
duce the SIGNAL
ATTENUATORS
to
as
low
a
setting
as
possible with
the
400
cycle
pattern still showing.
FIG. II.
DISCRIMINATOR
RESPONSE - 400 CYCLE
MODULATION
11.
Adjust the discriminator secondary
L9
in figure 8 until the 400
cycle
pattern
disappears
and then re-appears if
the adj1stment
is continued in
the same
dir
ection.
Be sure to
make this
adjustment to the
exact null
point with
the SIGNAL
ATTENUATORS
set
low to avoid a broad
response
due
to
a high signal
amplitude.
12. Adjust the discriminator primary L8
in
figure 8 until a
maximum ampli
tude
symmetrical
pattern
is
achieved
as shown in figure 7. Reduce the
F.M. ATTEN
UATOR setting
as
the
amplitude
of
the curve increases.
Readjust the
secondary if the
400
cycle modulation
reappears.
13.
Move the
OUTPUT cable to
the grid
of
the
next preceding
stage
point "D"
in
figure
8.
14.
Move
the
SIGNAL
INPUT connection to the grid of the
limiter point
‘C
‘
in
figure 8.
15.
Turn the
SIGNAL switch to UNMOD.
R,F. and
adjust
the F.M. and SIGNAL
ATTENTJATORSto
obtainani-f response curve
similar
to
figure
12.
The curve may
be
distorted until
the
next adjustment
has
been made.
-18-

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-
FIG. 12. SOUND I-F
RESPONSE
16. Adjust L7
and
L6
of
figure
8 for
a
symmetrical
response of
maximum height
similar
to
figure
12.
The
marker should appear
at
the
center. Keep
the F.M.
ATTEN
UATORS
set
as low as possible to avoid overloading and keep
the SIGNAL ATTEN
UATORS set low to
avoid
distortion of
the response curve at
the
marker
point.
17. Connect
the OUTPUT cable
to
the grid
of
the next
preceding stage
point
in
figure 8.
Adjust
L5
and
L4 for
a symmetrical response curve
of
maximum
height
as in
step 16
above.
The sound
i-f
adjustment
is
now complete. Adjustment of L2
and L3
was cov
ered
in video
i-f
alignment. However, if
this were an
f-rn
receiver instead of a
tele
vision receiver,
L2 and L3
would
be adjusted
to the intermediate frequency with
the
OUTPUT cable coupled to
the converter
grid. As the
alignment
proceeds from
the dis
criminator
back
to the
converter,thewidthof the
response curvewilidecrease sincethe
selectivity
of
the entire
amplifier is
greater than that of
any
one stage.
If the response
curve
becomes too
small, reduce the
F.M.
SWEEP. Any change in sweep
width will re
quire
re-adjustment
of the PHASING
control. Adjust the PHASING control
with
BLANK
ING
at
OFF.
If it is desired to
check the band pass
of the i-f system, connect the
OUTPUT cable
to
the grid
of the
converter tube and move
the
marker with
the
A.M.
Generator from
one side of the
response curve
to
the other.
i
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IJiL1
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tbf LLti hUId
-RJEC’
FIG.
13.
I-F BAND PASS MEASUREMENT
The band pass of a
resonant
circuit is
usually
taken between the 70% response points.
See figure 13. To
check
the
band pass of the i-f system, set the A.M.Generator
tuning
knob
to place
the
marker on the response
curve
at
the 70%
point
on one side
of the
curve.
Record
the
frequency indicated
on the
A.
M. Generator
dial.
Then
move
the
marker
to the
70% response point
on
the other side of
the
curve.
Record
the
frequency
indicated
on
the
A.
M.
Generator dial again. Then
subtract
the lower recorded
frequency
from
the higher
for the
band
of frequencies
passed
‘.
-19-