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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
shoul
d 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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