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I
odd 339A
Section
V
SECTION
V
ADJUSTMENTS
5-1.
INTRODUCTION.
5-2.
This
section
contains
complete adjustment
procedures
for the
Model 339A
Distortion
Measurement
Set.
After the
instrument has been adjusted according
to
the
procedures
given
in this
section,
it
should
meet
the
accuracy
specifications
listed in
Table
1-1.
5-3.
EQUIPMENT
REOUIRED.
Bf
The
test
equipment
required
to
perform
the
adjustments
is
listed at
the beginning of each
adjustment
procedure
and
in
the
Recommended
Test
Equipment
Table
in
Section
I.
If
the
recommended
equipment
is
not
available, substitute
equipment which
meets
the
critical
specifications
listed in
the table
may
be used
5-5.
ADJUSTMENT
LOCATIONS.
5-6.
The
Location of
all
adjustments
is
shown
in
Figure
5-3
at
the
back
of
this
section
The
function of
each
adjustment
is
listed in
Table
5-2.
5-7.
FACTORY SELECTED COMPONENTS.
5-8.
Certain
components
in
the
Model 339A
are
individually selected
to
compensate
for
varying
circuit
parameters.
These
components
are
noted
on
the
schematics
and
in
the material
list
by
an
asterisk
(*).
The
value
listed in
ihc
material
list
and on
the
schematic
is
the
pical
value of the selected
component.
The
function
of
e factory selected
components and
their
value ranges
are
listed in
Table
5-1.
5-9.
VOLTMETER ADJUSTMENTS.
5-10.
Mechanical Meter
Zero.
5-11
The
mechanical meter-zero should be checked and
adjusted,
if
necessary,
before
proceeding with
the
calibration
procedures.
The
meter-zero
is
checked
when
the
instrument
is
at
its
operating temperature
and
the
power
is
off.
The
meter
zero
is
correctly
set
when
the
pointer
rests
directly
over
the
zero
mark
on
the
meter
scale.
To
adjust the
meter-zero,
proceed
as
follows:
a.
Turn
the
instrument
on and
allow
it
to
"warmup"
for
at least
20
minutes
d.
Continue
rotating the
screw clockwise
until
the
pointer
is
exactly
over
the zero calibration
mark.
c.
Rotate
the
adjustment screw
slightly
counter-
clockwise
to
relieve
tension
on
the
pointer suspension.
If
the
pointer
moves
off zero, repeat
Steps
c
through
e.
but
make
the counter-clockwise rotation
less.
5-12.
Gain Adjustments.
Equipment
Required:
AC
Calibrator
(-hp-
Model
745
A).
Digital
Voltmeter
(-hp-
Model
3*t65A).
a.
Set the
339A
controls as
follows:
FUNCTION
INPUT LEVEL
FILTERS
OFF
(out)
METER
RESPONSE
VL
INPUT
RANGE
3
V
INPUT,
GND
SELECT
....
DIS.
AN.fi.
(center position)
b.
Set
the
AC
Calibrator
for
an output
of
3
V
at
1
kHz,
Connect
the
output
of
the
AC
Calibrator
to the
339A
DISTORTION
ANALYZER
input.
c.
Adjust
A2R17 (FULL
SCALE
ADJUST)
for
a
meter
indication
of exactly
3 V.
d.
Reduce
the
AC
Calibrator output
to
I
V
at
l
kHz.
e.
Adjust
A2R37
(1,3
SCALE
ADJUST)
for
a meter
indication
of exactly
I
V.
NOTE
The
adjust
men: of
A2R17
and
A2R37
interact.
Repeat
Steps h
through
e
until the
merer
indication
is
correct
<il
both Julhcaie
fj
V)
and
one-third
scale
f
1
V).
f.
Set the
AC
Calibrator
for
an output of 3.162
V
at
1
kHz.
Set
the
Digital
Voltmeter
to
measure
DC
volts
(20
volt
range).
b-
Turn
the
instrument
off
and
allow
approximately
30 seconds
for
all
capacitors to discharge.
g
Connect
the
DVM's
low
input to the
A2
assembly
shield
and
the
high input
to
A2TP2.
W
c.
Rotate
the zero
adjustment screw
clockwise
until
the pointer
is
left
of zero
and moving
up-scalc.
h.
Adjust
A2R36
(REFERENCE
ADJUST)
for a
DVM
reading of +3.162
V
dc
5-1
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