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HP 416A - Electrical Zero Adjustment

HP 416A
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3.
Connect
a
DC
vacuum
tube
voltmeter
,
such
as
a
Hewlett
-
Packard
Model
410B,
to
the
negative
terminal
of
capacitor
C70
.
Capacitor
C70
is
located
on
the
bottom
deck
of
the
Model
4 l
6A
and
is
i
dentified
in
Fig.
21.
The
negative
terminal
of
C70
is
just
opposite
the
center
tap
of
variable
resistors
R
118,
(Fig.
21).
Between
the
negative
terminal
of
C70
and
ground
should
meas
-
ure
-
6.
3V
with
a
line
voltage
of
l
15V
AC
.
If
this
indication
is
not
obtained
on
the
Model
410B,
variable
resistor
Rll8
may
be
adjusted
to
obtain
the
required
-
6.
3
volts.
Adjustment
of
HV
Output
Level
-
1.
Connect
a
DC
vacuum
tube
voltmeter
such
as
a
Hewlett
-
Packard
Model
410B
to
pin
3
of
Vl9
(Fig
.
21)
.
Between
pin
3
of
Vl9
and
ground
should
measure
+250
volts
with
a
line
voltage
of
l
15V
AC.
2.
If
this
indication
is
not
obtained
on
the
voltmeter,
variable
resistor
Rll6
(Fig.
21)
may
be
adjusted
to
obtain
the
required
+
250
volts
.
Line
Regulation
-
1.
Set
the
variable
transformer
so
that
the
line
voltage
to
the
Model
416A
will
be
at
103
.
5V
AC
and
then
at
126
.
5V
AC.
2.
The
indication
on
the
DC
vacuum
tube
voltmeter
connected
to
pin
3
of
Vl9
should
remain
at
+
250
volts
regardless
of
variations
between
103,
5
and
12
6.
5
volts
in
the
power
supply
input
.
3.
If
the
regulator
output
voltage
varies
with
input
voltage
variations,
see
Trouble
-
Shooting
Chart
,
step
2
under
"HV
Regulator
not
functioning".
Calibration
-
The
calibration
procedure
consists
of
adjusting
the
meter
circuit
for
electrical
zero
and
electrical
full
scale
.
Remove
the
cab
-·
inet
from
the
Model
416A
before
starting
the
calibration
procedure
.
Test
Set
-
Up
: -
For
the
calibration
adjustments
,
equipment
shou
ld
be
arranged
as
shown
in
Fig
.
18
.
Note
that
the
cable
which
extends
the
connection
from
attenuator
#2
to
the
REFLECTED/PROBE
connector
on
the
Model
416A
is
fitted
with
a
shielded
dual
banana
plug
.
The
res
i
stor
across
the
output
of
attenuator
#2
may
be
connected
ins
i
de
the
connector
shield
as
shown
in
De
-
tail
1.
To
avoid
injection
of
noise
from
external
sources
into
the
low
-
noise
amplifier
circuits
of
the
Model
416A
,
the
units
shown
in
Fig
.
18
should
not
be
connected
to
an
existing
bench
or
test
stand
ground
.
Electrical
Zero
Adjustment
:
1.
The
input
to
attenuator
#1
is
to
be
10
volts
at
1
kc
.
Set
the
audio
oscillator
for
an
output
of
1
kc
at
such
level
that
a IO -
volt
reading
is
obtained
on
the
voltmeter
connected
across
the
input
to
attenuator
#1.
2.
At
the
Model
416A,
disconnect
the
reflected
input
cable
from
the
REFLECT
ED
/PROBE
connector
.
-
52
-

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