Hewlett-Packard AR Operating And Servicing Manual
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SECTION
III
MAINTENANCE
3
-1
COVER
REMOVAL
You
will
be
able
to
slide
the
one-piece
cover
off
of
the
instrument
after
removing
the
four
screws
in
the
rear
of
the
cover.
3-2
TUBE
REPLACEMENTS
In
many
cases
instrument
malfunction
can
be
corrected
by
replac-
ing
a
weak
or
defective
tube.
Before
making
any
internal
adjust-
ment
or
component
replacement,
check
the
tubes.
Adjustments
made
in
an
attempt
to
compensate
for
a
defective
tube
will
often
complicate
the
repair
problem.
It
is
good
practice
to
check
tubes
by
substitution
rather
than
by
the
use
of
a
"tube
checker".
The
res
ults
obtained
from
the
"tube
checker"
can
be
misleading.
Mark
original
tubes
to
insure
return
to
the
same
socket.
Replace
only
tubes
proved
to
be
weak
or
de-
fective.
Any
tube
with
corresponding
standard
EIA
(JEDEC)
characteristics
can
be
used
as
a
replacement.
3-3
POWER
SUPPLY
Rectifier
CRI
is
connected
in
a
half-wave
circuit.
The
dc
output
voltage
between
ground
and
the
junction
of
C96
and
L25
should
be
11 0 ±:lO
volts
with
the
line
voltage
set
to
115
volts.
The
GAIN
control
should
be
set
fully
clockwise
to
maximum.
Ripple
voltage
can
be
quite
high
without
affecting
instrument
performance.
Low
power
supply
voltages
are
generally
due
to
a
weak
selenium
rectifier,
leaky
filter
capacitors,
shorted
tubes
or
off
value
plate
line,
grid
line,
or
screen
resistors.
3-4
230
VOLT
OPERATION
The
r$fJ
Model
460AR
can
be
quickly
and
easily
converted
to
operate
from
a
nominal
230
volt
50/1000
cps
power
source.
The
instrument
is
normally
supplied
with
the
dual
primary
windings
of
the
power
transformer
connected
in
parallel
for
115
volt
operation.
To
con-
vert
for
230
volt
operation,
reconnect
the
primary
windings
in
series
as
shown
on
the
schematic
diagram.
The
line
fuse
F I
must
also
be
changed
from
O.
6
amp.
slow-blow
to
0.4
amp.
slow-blow.
-7-