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Model
339A
Section
III
should
indicate
-3dBV±2dB.
Return
the
filter
switch
to
off
(out).
h.
Set the
FREQUENCY
controls for a
frequency
of
80
kHz. Readjust
the
level
vernier for a
meter
indication
of 0
dB V
if
necessary.
i.
Set the
80
kHz
filter
switch
on
(in).
The
meter should
indicate
-3
dB V
±
2
dB.
Return
the
filter
switch
to off
(out).
3-56.
OPERATOR'S MAINTENANCE.
3-57.
Fuse Replacement.
3-58.
The
ac
line
fuse
is
located
on
the rear
pane! of
the
instrument.
Before
checking
or
replacing
the
fuse,
disconnect
the ac
line
cord
from
the
instrument.
The
fuse
used
in
the
Model 339A
is
a
250
mA,
normal-blow
fuse.
WARNING
|
'
For continued
protection
against
fire
hazard,
replace
only
with the
same
type
and
rating
of
fuse
as specified
for
the
line
voltage being
used.
3-59.
Adjustment
of
Meter Mechanical
Zero.
3-60.
The
meter
is
properly
zero-set
when
the pointer
rests
over
the zero calibration
mark
with
the
instrument
in
its
normal
operating
environment and
turned
off.
Zero-set
the
meter
as
follows
to
obtain
maximum
accuracy
and
mechanical
stability:
a.
Turn
instrument
on and alow
it
to
operate
for
at
least
20 minutes
to
let
meter
movement
reach
normal
operating temperature.
b.
Turn
instrument
off
and
allow 30 seconds
for
all
capacitors
to
discharge.
c.
Rotate
zero
adjustment
screw
clockwise
until
pointer
is
left
of zero
and
moving
upscale.
d.
Continue
rotating
screw
clockwise;
stop
when
pointer
is
exactly
at zero.
e.
When
pointer
is
exactly
over
zero,
rotate
adjustment screw
slightly
counterclockwise
to
relieve
tension
on
pointer suspension.
If
pointer
moves
off zero,
repeat
Steps
c
through
e.
but
make
counterclockwise
rotation
less.
3-7 3-8
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