HP 400D Operating And Servicing Manual page 26

IV
Sect. Page S
4)
Change input signal to 6. 4 mc and set amplitude
to "SET LEVEL".
5) The reading on the vtvm under test should not
c1
be more than 5% full scale aoove
0 . 90
ing below i s acceptable.
pt:!ak Is
undesirable at frequencies above
H
the reading is more than 5% high, add capacitor
if
C40 and resistor R 82
circuit of V2 in your vtvm.
if
5 these parts are added.
RS2
C40
The values of and
the 6. 4 mc response below the 5%
change either R82 or C40 in value, repeat steps
I through 5 .
Change the input signal to
6)
plitude to "SET L E V E L " step
test
vtvm
the under should be
10
To increase the
cps indication, remove
present in V2 grid circuit.
if
cuit additional increase is needed after
moval. Conversely, to decrease the indication,
RSa
remove RSI and add
be
can omitted. A value of 2 . 2 megohms or higher
RSO
should be used for
frequency response. Check tubes and coupling capa­
citors if you find that a resistor value below 2.2 meg­
ohms is required.
7)
Inc rease the input signal to about 20 cps and
set the amplitude to "SET LEVEL" of step 1.
vtvm
reading on the
under test should not be more
than ± 2 % of full scale from
make compromise resistor adjustments to satisfy
steps 6 and 7.
S)
Switch the vtvm under test to the
range . E stablish a new
0. 90
with a reading of
vtvm under test.
the
9)
Change input signal to
amplitude to the "SET LEVEL" established in step
Set the reading on the vtvm under test to
adjusting capacitor C14.
the vtvm
10)
Switch under test
400
Establish a new cps "SET LEVEL" with a read­
the 0 to 1
of
0. 90
ing on scale
ll)
Change the input signal to
amplitude to the "SET LEVEL" establ1shed In step
10. Set the reading on the vtvm under test to
by adjusting-capacitor C16.
0.90.
Any read­
A high frequency
4
mc.
not already in the cathode
Repeat steps I through
can be adjusted to bring
maximum. H
you
10 cps and set the am­
1.
The reading on
of
0. 90,
±5% full scale.
RBO
Add Ral in V3 grid cir­
RSO
re­
if
necessary. Either but
Both resistors
or RSl when adjusting low
The
H
0 . 90.
necessary,
0. 003
volt
400
cps "SET LEVEL"
0 1
on the to scale of the
4
mc and set the input
0. 90
to the volt
0.01
range.
of vtvrn
the under test.
4
mc and set the input
0. 90
12) Check frequency respOnse on
0. 3
volt ranges. Establish a
for each range and then check the response at 4 mc.
H
an error greater than ± 5% of full scale is noted,
make a compromise adjustment
of C2l is changed, repeat all previOUS steps except
6 and 7 The compromise setting of C2l must be
used when repeating step
13)
Switch the vtvm under test to the
400
Establish a new
the
of
0.90 0
ing on
14} Change the input signal to 2
amplitude to the "SET LEVEL" established in step
13. Adjust capaCitor C4 for a reading of
15) Change the input Signal to 4 mc and set the am­
plitude to the "SET LEVEL" established in step 13.
The reading on the vtvm under test should not be
of
more than ±2%
if
Adjust R6 in the input divider to bring the
response within ±2%.
several parallel resistors.
of R6 will raise the frequency response at
Lowering the re sistance will decrease the 4 mc
response.
16) The frequency response
H
be checked. othe r ranges have been properly
adjusted range will be
this
K.
The following frequency response adjustment pro ­
cedure Is based upon the use of the alternate test
eqUipment as explained in paragraph
following procedure, test frequencies of 10 cps,
1
4
mc, mc, and 6. 4 mc are given.
4
mc frequencies are the band limits of the volt­
meter. The 6. 4 mc check point is for determining
high frequency performance.
The input voltage to the
be monitored by a reference volbneter having a
frequency respJnse.
B,
400
ing at cps will be called "reference level" in all
by
steps that follow.
The frequency response
prol:ably not need adjustment.
included to verify the instrument response and to re­
store proper operation in case
is altered. fi'ailure to meet any
can usually be traced to one or more weak tubes.
the
0. 03, 0
400
cps "SET LEVEL"
of H
C21. the setting
3.
1. 0
volt range .
cps "SET LEVEL" with a read­
1
to scale of the vtvm under test.
kc
0
and set the input
O. 90.
0. 90.
full scale from
This resistor consists of
Increasing the resistance
of
3
the volt range can
specifications.
within
4-5,
10
The
vtvtrl
under test must always
The reference voltmeter read­
NOTE
controls in the
rwne
inst
These steps have been
the
original adjustment
of
the following tests
. 1, and
4
mc
4 mc.
In the
cps and
known
will
nt