HP 400D Service Note

400D-2C
If you change or add these parts, repeat steps a and b.
Use same range and reference level as step a. A re-
sponse that “falls-off’’ above 4 mc is more desirable
than one that rises.
d. The 10 to 20 cps.responseadjustment varies with
voltmeter circuitry.
If cathode resistors R38, R47, and R53 for tubes V3,
V4, and V5 respectively all have values of 100 ohms,
the value of R45
in the plate circuit of V4 can be ad-
justed between limits of 0.75 and
1.0 megohms to
adjust the 10 to 20 cps response.
In any instrument, to increase the 10 cps indication,
remove R80 if present in V2 grid circuit. Add R81 in
V3 grid circuit
if additional increase is needed after
R80 removal. Conversely, to decrease the indication,
remove R81 and add R80
if necessary. Either but not
both resistors can be added. Both resistors can be
omitted.
A value of 2.2 megohms or higher should be
used for R80 or R81. Check tubes, cathode capacitor
C20, and coupling capacitors
if you find that a resistor
value below 2.2 megohms is required.
e. Adjust C14 at
4 mc on the .003-volt range after
establishing a 400 cps “reference level” on
the
same range.
f. Adjust C16 at 4 mc on the .Ol-volt range after
establishing a 400 cps “reference level” on
the
same range.
g. Check frequency response on the .03, .l, and .3
volt ranges. Establish a 400 cps “reference
level” for each range and then check response at
4 mc. If an error greater than f 5% of full scale
is noted, make a compromise adjustment of
C21.
If you change C21, repeat steps a, b, c,
d, e, and
f. The compromise setting of C21
must be used when repeating
step a.
h. For “CAPACITIVE INPUT DIVIDER” Circuits
See step
E in Section IV to de-
Skip
step i.
termine input circuit type.
i. For “RESISTIVE INPUT DIVIDER” Circuits
Adiust C4 at 20 kc on the
1.0 volt range after
esiablishing a 400 cps “reference level” on
the
same range.
j. Adjust R6 in the input divider to bring the 4 mc
response
within specifications on the 1 .O-volt
range after establishing a 400 cps “reference
level” on the same range.
This resistor consists of several parallel resistors.
Increasing the resistance of R6 will raise the response
at
4 mc. Lowering the resistance will decrease the
4 mc response.
00665-2
Page 7
k. The response of the 3-volt range can now be
checked.
If other ranges have been properly ad-
justed, this range
will be within specifications.
The response of any range can now be checked
at any frequency between 10 cps and
4 mc.
2) For Models 400D/H/L with serials prefixed 017-:
a. Adjust C102
“HIGH FREQUENCY COMP” at
4 mc on the 0,001 volt range after establishing a
400 cps “reference level” on the same range.
b. The oscillator should now be tuned through the
band of
4 mc to 10 mc. Note the voltmeter indi-
cation during this time;
If the reading increases
more than
2% above the 4 mc level, adjust AM-
PLIFIER BIAS control R119 counterclockwise,
and repeat
4 mc ad‘ust (step a above).
Repeat
the
4 mc response. Note: Be sure reference
meter
is set at SET LEVEL.
this procedure unti II peaking is less than 2% of
c. Set oscillator output to “reference level”. Adjust
LOW FREQUENCY RESPONSE control R118 to
bring the 10 to
20 cps response within specified
limits. If R118 will not bring both the 10 and 20
cycle response into specifications, the AMPLI-
FIER BIAS control R119 must be readjusted
so
that R118 can bring the 10 and20cycle response
within limits.
d. If R119
is adjusted during the low frequency re-
sponse calibration (step c),
it will be necessary
to repeat the high frequency response adjust-
ment in step b. The adjustment of R119 will be
a compromise to meet both low and high
fre-
quency specifications.
e. Adjust C14 at 4 mc on the 0.003 volt range after
establishing a 400 cps reference level
on the
same range.
f. Adjust C16 at 4 mc on the .01 volt range after
establishing a
400 cps reference level on the
same range.
g. Adjust C4 at 20 kc on the 1.0 volt range after
establishing a 400
cps reference level on the
same range.
h. Adjust R6 in the
input divider to bring the 4 mc
response
within specifications on the 1.0 volt
range after establishing a 400 cps reference
level on the same range.
R6 consists of several
resistors connected
in parallel. Increasing the
sponse at
4 mc. Lowering the resistance will
decrease the
4 mc response. Note: Be sure
input shield
is in place before taking reading.
resistance of R6
will raise the frequency re-
\
N. FINAL CHECK AND ADJUSTMENT
in steps
G and H.
Repeat the Basic Calibration procedures given

HP 400D Specifications

General

Brand	HP
Model	400D
Category	Measuring Instruments
Language	English