HP 400D Owner's manual

OPERATING AND SE RVICING MANUAL
FOR
MODEL 40OD/H
VACUUM TUBE VOLTMETER
MODEL 4OOD
Serial 179?1 and above MODEL 4OOH
Serial 2238 and above
Copyright HEWLETT-PACKARD COMPANY 1955
275 PAGE MILL ROAD, PALO ALTO, CALIFORNIA, U.S.A.
400DH001-1

SPECIFICAT!ONS
MODEL 4OOD
VOLTAGE RANGE:
0.1 millivolt to 300 volts.Twelve ranges
selected with front Panel switch.
FulI scale readings of:
0.001
0.003
0.010
0.030
0.100
0. 300
1.000
3.000
10.00
30.00
100.0
300.0
DECIBEL RANGE:
-72 lo +52 db, in 12 ranges.
FREQUENCY RANGE:
10 cps lo 4 mc/s.
ACCURACY:
With line voltage of 115 volts, t1ffi
(103 to 127 volts), overall accuracy is
within:
x21o of full scale value, 20 cps to 1 mcl
x37o of. full scale value, 20 cps to 2 mcl
+\Voof. full scale value, 10 cps to 4 mc.
LONG TERM STABILITY:
Reduction in Gm of amplifier tubes to 7570
of nominal value results in error of less
tfian U.\Eo, 20 cps to 1 mc.
CALIBRATION:
Reads rms value of sine wave. Voltage
indication proportional to average value
of applied wave. Linear voltage scales,
0 to 3.0 and 0 to 1.0; db scale, -12 db to
+2 db, based on 0 dbm = 1 mw in 600
ohmsl 10-db intervals between ranges.
MODEL 4OOH
0. 1 millivolt to 300 volts. Twelve ranges
selected with front Panel switch.
Full scale readings of:
0.001
0.003
0.010
0.030
0.100
0. 300
1.000
3.000
10.00
30.00
100. 0
300.0
-72 to +52 db, in 12 ranges.
10 cps to 4 mc/s.
With line voltage of 115 volts, +10/6
(103 to 12? volts), overall accuracy is
witfiin:
tt%of. full scale value, 50 cps to 500 kc;
nflo d full scale value, 20 cPs to 1 mc;
+Wo of full scale value, 10 cps to 4 mc.
Reduction in Gm of amplifier tubes to 757c
of nominaL value results in error of less
than 0.\Va, 20 cps to 1 mc.
Reads rms value of sine wave. Voltage
indication proportional to average value
of applied wave. Linear voltage scales,
0 to 3.0 and 0 to 1.0; db scale, -12 db to
+2 db, based on 0 dbm = 1 mw in 600
ohmsl 10-db intervals between ranges.

SPECtFICATTONS (CONT'D.)
MODEL 4OOD
INPUT MPEDANCE:
10 megohms shunted by 15 p1"rf on ranges
1.0 to 300 volts; 25 pt on ranges 0.001
volt to 0.3 volt.
AMPLIFIER:
Output terminals are provided so volt-
meter can be used to arnplify srnall sig-
nals or to inonitor waveforms under
test with an oscilloscope. Output ap-
proximately 0. 15 volt rms on all ranges
with full-scale meter deflection. Aarpli-
fier frequency response sarne as that
of voltmeter. Internal impedance approx-
imately 50 ohms over entire frequency
range.
POWER SUFFLY:
tl5/230 volts, + l}Eo, 5Q/1000 cps, ap-
proximately 70 watts.
SIZE:
Cabinet Mount - t1-l/2 inches iligh,
- 7 -L/2 inches wide,
- 12 inches deep.
Rack Mount - 7 inches high,
- 19 inches wide,
- ll-3/4 inches deep.
WEIGHT:
Cabinet Mount - 18 lbs.; shipping .veight
approx. 25 lbs.
Rack Mount - 22Lbs.; shipping weight
approx. 35 lcs.
ALSO EVAIL.TIBLE:
@vloaet 400D-db, with a special meter
face having the db meter scale uppermost
to permit greater resolution in db read-
ings.
MODEL 4OOH
10 megohms shunted by L5 gfi. on ranges
1.0 to 300 volts; 25 ptrrf on ranges 0.001
volt to 0.3 volt.
Output terminals are provided so volt-
meter can be used to amplify small sig-
nals or to monitor waveforms under
test with an oscilloscope. Output ap-
proximately 0. 15 volt rms on all ranges
with full-scale meter deflection. Ampli-
fier frequency response same as that
of voltmeter. Internal impedance approx-
imately b0 ohms over entire frequency
range.
lL5/230 volts, r1ffi, 50/1000 cps, ap-
proximately 70 watts.
Cabinet Mount - ll-l/2 inches high,
- 7-l/2 inches wide,
- L2 inches deep.
Rack Mount - 7 inches high,
- 19 inches wide,
- lL-3/4 inches deep.
Cabinet Mount - 18 lbs.; shipping weight
approx. 25 lbs.
Rack Moturt - 22 Los.; shipping weight
approx. 35 lbs.
,iE tvioAet 400H-db, with a special meter
face having the db meter scale uppermost
to permit greater resolution in db read-
ings.
;
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(, CONTENTS
SECTION IGENERAL DESCRIPTION Page
-1
-1
-1
II-1
II-1
1-1
t-2
1-3
t-4
1-5
General Description
Damage in Transit
Power Line Voltage
Power Cable
Accessories -t
-2
SECTION II OPERATING INSTRUCTIONS
2-l
2-2 Controls and Terminals .
Operation
3-1
3-2
3-3
3-4
i* SECTION III THEORY OF OPERATION
SECTION IV MAINTENANCE
TABLE OF REPLACEABLE PARTS
General
Input Voltage Divider
Amplifier, Rectifier and Meter
Power Supply
Introductory .
Meter Zero Adjustment
Case Removal
Capacitor Replacement
Replacement of Crystal Diodes
Tube Replacement
Adjustments
Trouble Shooting
Power-Supply Localization Checks
Voltmeter Localization Checks
m
trI
III
UI
-1
-1
-2
-4
I
4-1
4-2
4-3
4-4
4-5
4-6
4-7
4-8
4-9
4-10
ry
ff
w
ry
ff
ry
w
ry
ff
ry
-1
-1
-1
q
-5
-7
-10
- 11
SECTION V
5-1 Table of Replaceable Parts v-1

CAUTION
The ground terminal (G) of the INPUT and OUTPUT binding posts, the instru-
ment chassis and cabinet, and the third (green) grounding conductor in the
three -conductor power cable are electrically connected together at aII times.
When the NEMA connector is used in the proper manner, a ground path is
established between the 400D/H and equipment which is also grounded. Do not
connect the ground terminal of the instrument to any point which is not at
ground potential, or a short circuit wiII be created. If such a measurement
is necessary, disconnect the NEMA ground in the power cable by using an
adapter with the grounding pig -tail removed, and the cabinet insulated from
ground. The 400D/n cabinet wiII be at the same potential as the ground Iead.
Caution must be used if the clip lead is connected to a point which is more
than a few volts off ground. Because of the potential hazard to personnel,
this method is not recommended.
One side of almost all power distribution systems is grounded. Extreme cau-
tion must be used if direct measurement of power system voltages is attempted.
If the ground Iead is accidentally connected to the ungrounded side of the Iine,
severe damage to the 40 OD/H is possible because of the short circuit created.
Fower line voltages can be safely measured by using the ungrounded (upper)
terminal only. Contacting the grounded power conductor will give a reading
of 0 volts, while contacting the ungrounded lead wiII give full line voltage
reading.
When very low level voltages are being measured, there is a possibility of
error caused by current flowing in the equipment grounding conductor and the
ground signal input conductor. This current flow will cause a voltage to be
developed in the connecting leads which is in series with the signal under
measurement and wilt be read by the meter. This source of error can be re-
moved by eliminating the ground toop between the meter and the circuit under
test.
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Sect. I Page 1
stcTr0lr r
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I.I GENERAL DESCRIPTION
Throughout this manual, where reference is made
to the 400D the information applies equally to the
400H. The major differences between the two in-
struments are tolerance refinements and a more
accurate meter movement in the Model 400H.
The Model 400D Vacuum Tube Voltmeter is an accu-
rate ard sensitive average-req)onding rms calibrated
voltmeter which will measure a-c voltages from 0.001
volt full scale to 300 volts full scale over a frequency
range of 10 cycles to 4 megacycles. It has an input
impedance of 10 megohms, effectively preventing
disturbance to circuits under test. The distinctive
features of this voltmeter make it valuable for mea-
suring.gain, network response, and ou@ut level witl
speed and accuracy. The wide frequency range makes
it suitable for audio, r-f, and video measurements.
The sensitivity of t}re voltmeter is sufficient in many
instances to measure hum and noise level directly.
The 400D voltmeter also may be used as an audio
level (VU) meterl as a high-gain broadband ampli-
fier to give increased sensitivity to oscilloscopes,
bridges, and other equipment requiring additional
o
Table 1-1. Ranges
Switch
Designator Voltage
Range Decibel.
Range
-60 .0001
-50 .003
-40 .01
-30 .03
-20 .1
-10 .3
10
3 +10
10 +20
30 +30
100 +40
300 +50
0 to 0.001
0 to 0.003
o to 0.01
0 to 0.03
0to0.1
0to0.3
0to1
0to3
0to10
0to30
0 to 100
0 to 300
-72 to -58
-62 to -48
-52 to -38
-42 to -28
-32 to -18
-22to - I
-l2to+ 2
- 2to+12
+ 8to+22
+18 to +32
+28 to +42
+38 to +52
GEl{TRAT DTSCRIPTIO]{
sensitivity; and to detect nulls. In conjunction with
an oscilloscope, the voltmeter may be used to monitor
waveforms, and in conjunction with an oscillator,
may be used to measure wide ranges of L and C as
well as moderate ranges of R and Z. The 400D also
may be used as an indicating device to measure
coil Q.
T.2 DAMAGE IN TRANSIT
If upon initial inspection this instrument is found
to be damaged in any way, refer to CLAIM FOR
DAMAGE IN SHIPMENT for the necessaly instruc-
tions. (See last page in instruction manual. )
I.3 POWER LINE YOTTAGE
When the instrument leaves the factory normally
it is wired for 115-volt operation. ff it is desired to
operate the instrument from a 230-volt source, refer
to the transformer conversion data on the schematic
diagram for the correct procedure.
As shown on the schematic diagram, the alteration
changes the primary windings of the transformer
from a parallel (for 115-volt input) to a series (for
230-volt input) arrangement.
I.4 POWER CABTE
The three conductor power cable supplied with this
instrument is terminated in a polarized three-prong
male connector recommended by the National elec-
trical Manufacturersr Association. The third con-
tact is an offset round pin, added to a standard two-
blade connector, which grounds the instrument chas-
sis when used with the appropriate receptacle. To use
this NEMA connector in a standard two-contact re-
ceptacle, a three-prong adapter should be used.
The ground connection emerges from the adapter
as a short lead which should be connected to a
grounded receptacle box for the protection of oper-
ating personnel.

Sect.I Page 2
r.5 ACCESSOR.IES
Accessories available for use with the Model 400D
Vacuum Tube Voltmeter are listed below. These
accessories are not supptied with the instrument
but may be purchased from the Hewlett-Packard
Company.
Model AC-60A Line Matching Transformer -
t to 600
otrm unUatanced output, for measurements on bal-
anced lines.
Terminating Resistance:
600 ohms or 10,000 ohms
FrequencY Range:
5 kc to 600 kc
Power Handling CaPacitY:
+22 dbm (10 volts at 600 ohms)
Balance:
Better than 40 db, entire frequency range
Model AC-60B Line Bridging Transformer -
unbal-
anced output, for measurements on balanced lines'
Terminating Resistance:
600 ohms or 10,000 ohms
Frequency Range:
20 cps to 45 kc
Power Handling CaPacitY:
+15 dbm (4.5 volts at 600 ohms)
MoCel 452A Capacitive Voltage Divider -
Division ratio: 1000:1
Model 4StCapacitive Voltage Divider -
Division ratio: 100:1
Accuracy: +370
Frequency range: 20 cps to 4 mc
Input Impedance: 50 megohms shunted with 2' 75 u4u.f'
Maximum Voltage: 1500 volts
Model 4?0A thru 470F Shunt Resistors -
These shunt resistors adapt the Model 400D for
measuring currents as small as 1 microamp full
scale.
Accuracy: +l\o lo 100 kc, 470A-F
+SVo to 1 mc, 470A
+}Vo to 4 mc, 4708-F
Maximum Power
dissipation: 1 watt
Accuracy:
Input caPacitY:
Maximum volt-
age rating:
xflo
15 gi., +1 grf
60 cps 25 kv
1mc 20kv
20 mc ?kv
100 kc 221r.t
10 mc 15 kv
Model
a70r
470B
470C
470D
4?08
470F
Shunt Resistance
--T'.I-oIms -
1. 0 ohms
10.0 ohms
100.0 ohms
600.0 ohms
1000.0 ohms

Sect.II Page 1
sEcTl0il il
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2.1 CONTROLS AND TERMINALS
oN-
T-his toggle switch closes the Iine voltage to the
power-supply transformer. With the switch at ON,
the red indicator lamp will glow as soon as the power
transformer is energized.
DB VOLTS
TE'G wmFtype rotary switch connects the proper
multiplier resistors and capacitors into the circuit
for the desired voltage range. The position of the
switch indicates 1) the full scale voltage of ttre range
in use and 2) the db level, when the m d.er pointer
is at zero on the DECIBELS scale. Lirnits of each
range are shown in Table 1-1.
INPUT AND OUTPUT TERMINALSPUT are con-
nected to the input circuit of the instrument. The
two binding posts designated OUTPUT are the output
terminals for the amplifier. The lower binding post
in each pair, designated G is connected to tfie Chas-
sis. The binding posts will accommodate either a
banana plug or wire, and are so arranged that any
double banana plug with a 3/4 Lnch spacing may be
used.
CAUTION
The maximum voltage (the sum of the d-c voltage
and a-c peak voltage) applied to the input terminals
of the Model 400D Vacuum Tube voltmeter must not
erSggd_qlqJglts. Higher voltages will break down
the capacitors in the input system of the instru-
ment.
METER
mA ,i00-D meter is a d-c milliammeter calibrated to
indicate the rms value of a sine wave.
FUSE
if[E-fuseholder, Iocated on the back of the instru-
ment, contains a l-ampere cartridge fuse which is
OPERATII{G I}ISTRUGTIO}IS
in the power supply input circuit. Replacement fuses
must be of the rtSlo-Blot' type as specifiedin the
Table of Replaceable Parts.
NOTE
When the power transformer is connected for 230-
volt operation, use a l/Z-ampere " Slo-Blo, car-
tridge fuse.
2.2 OPERATION
When the Model 400D is received from the factory,
the meter pointer should indicate zero before the
instrument is turned ol. If it does not, adjust the
pointer to zero as explained under Section IV,
paragraph 4-2. After the instrument is turned on,
the meter pointer may show an indication of as much
as two scale divisions, principally on the one-milli-
volt range. This effect is normal and does not im-
pair the accuracy of the instrument.
On the lowest three ranges of the instrument the
high input impedance coupled with the gain of the
amplifi.er causes the meter needle to be forced
against the right-hand stop of the meter when the
input terminals are unshielded. This condition is
normal and is caused by stray voltages in the vicinity
of the instrument.
If measurements are made from a high-impedance
source, hum pick-up can affect the meter indication
because of the high impedance of both the source and
the Model 400D. Shielded leads wiil reduce pick-up,
although they wiil cause an increase in the capacity
shunted across the source, with the possibility of
excessive circuit loading.
a. VoltageMeasurements
rct ptugged intoapower
source of specified voltage and frequency, and the
toggle switch at ON, allow the instrument about
five minutes to reach a state of stable operation.
o

Sect.II Page 2
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Figure 2-1. Model 400D/H Impedance Correction Graph