16.1
Adjustment
If readings are
not
correct, repeat steps
14
and
15
and check the bridge resistors
R37/
SOO
ohms,
R38/
60 ohms,
R39/40
ohms,
R40
/40
ohms,
R41/60
ohms and
R42/500
ohms
for
proper value. Note
that
resistors
of
equal
value
in
this series should
be
matched closely
in
value
for
good bridge balance. Also check
the
main
meter
movement and verify
that
it
indicates full
scale
when exactly 115
~
are
passed
through it. The metal plate
mounted on the side
ofthe
meter
is
a factory applied magnetic shunt.
By
loosening
the
mounting screw and
slidingthe plate back
and
forth, small adjustments
can
be
made
to
the full scale deflection
of
the
meter.
1ft
he
meter reads
too
high
with
1151-1A,
adding a large value resistor across
the
meter terminals
can
shunt some of the
current around
the
meter
allowing
it
to
read correctly.
The
value
of
the resistor
can
be calculated
orfound
by trial
and error.
Ifthe
meter
reads
too
low
with
1151-1A
it
requires
takingthe
meter
apart and making major repairs
far
in
excess
of
the
scope
of
this document. Bear
in
mind
that
changingthe
meter
range will also affect the readings
of
the
other
functions it
pe
rforms
so
rule
out
eve rything else before adjusting the meter.
17
MUTUAL
CONDUCTANCE CALIBRATION USING A
CALIBRATION TUBE
Set the FUNCfION switch
to
the C (15,000) position.
Set
the
BIAS
RANGE
switch
to
the
10
volt position. Complete
the
usual setup
for
a type 6L6
tube
setting
the
bias
adjustment
for
3.00 volts. Insert a calibrated
6L6
tube into
the
octal socket and allow
ittowarm
upfora
minimum
of
five minutes.
Push
P4
(locked). Readjust
the
AC
line voltage
to
the red line on the
meter
and
BIAS
VOLTS
control
to
3.0
volts while the
P4
button
is
depressed. Observe
the
mutual conductance reading. If
the
reading
is
more than one division high
or
low
of
the
calibration value
of
the
tube, the grid signal must
be
adjusted
to
make
the
reading correct.
Be
sure
that
the tester
is
blocked up and
resting
in
its normal operating position
orthe
meter
calibration may
be
inaccurate.
Release
P4
and remove the
6L6
from
the
octal socket.
If a calibrated 6L6
is
not available a reasonable calibration
will
be
done
by
performing steps
11
(GRID
SIGNAL
VOLTAGE
TEST)
and
15
(METER
BRIDGE
BALANCE)
above.
The
calibration tube test
will
verify
that
all adjustments
have been
successful.
18 DIODEIRECTIFIER TESTS:
A.
Verify
that
the panel switches are set up
to
the
conditions
as
given in the list immediately
following
step 6.
(HS
5348-1) & FILAMENT
at
6.3 volts. Set the
BIAS
and
the
ENGLISH
controls
to
zero. Connect a
lK,
lOW,
1% resistor
to
the
anode lead
of
a
lN4005
silicon rectifier. Connect the cathode
of
the
rectifier
to
pin 8
of
the
octal socket. Connect
the
other
lead
of
the
resistor
to
pin 3
of
the
octal socket.
Adjust
the
SHUNT control
to
24.
Press
the
PI
DIODE
test
button.
Verify
that
the
meter
reads
at
or
slightly above the
DIODES
OK line on the meter.
Release
Pl.
B.
Adjust
the
ENGLISH
control
to
83.
Press
the
P3
RECfIFIER
test
button.
Verify
that
the
meter
reads
at
or
slightly above the
DIODES
OKline
on the meter. Note:
for
actual rectifier
tube
tests
the
REPLACE?
GOOD
scale
is
read
forthe
test
results.
Release
P3.
C.
Replace
the
lK
resistor
with
a 10K,
lOW,
1% resistor. Adjust
the
ENGLISH
control
to
79.
Press
the
P2
OZ4
test
button. Verify
that
the
meter
reads
at
or
slightly above
the
DIODES
OK line on
the
meter.
Note:
for
actual
OZ4
rectifier
tube
tests
the
REPLACE?
GOOD
scale
is
read
for
the
test
results. Release
P2.
18.1
Adjustment
The
diode and rectifier tests measure the voltage
drop
across
the
rectifier by applying a fixed voltage
with
a
series
limiting
resistor and measuring the available plate current.
If
the
readings are
not
correct
for
any
of
the
Pl,
P2
or
P3
tests check resistors
Rl/150
ohms,
R6/1.2K,
R7
/1.8K.
The sensitivity
of
the
meter
and
the
accuracy
of
the transconductance circuits also affect this test.
28
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