HP 333A Service manual

OPERATING AND SERVICE MANUAL
MODEL 333A/334A
DISTORTION ANALYZER
Serial Numbers:
333A: 1137А03146 and greater
334A: 1140А05641 and greater
Appendix С, Manual Backdating Changes, adapts this manual to
lower serial numbers.
WARNING
To help minimize the possibility of electrical fire or shock
hazards, do not expose this instrument to rain or excess moisture.
Manual Part No. 00333-90008
Microfiche Part No. 00333-90058
Copyright Hewlett-Packard Company 19 66
P.O. Box 301, Loveland, Colorado, 80537 U.S.A.
Printed: October 1975

HEWLETT ш PACKARD
CERTIFICATION
Hewlett-Packard
Company
certifies
that
this
instrument
met
its
published
specifications at the time of shipment from the factory. Hewlett-Packard
Company further certifies that its calibration measurements are traceable to the
United States National Bureau of Standards, to the extent allowed by the
Bureau’s calibration facility, and to the calibration facilities of other
International Standards Organization members.
WARRANTY AND ASSISTANCE
This Hewlett-Packard product is warranted against defects in materials and
workmanship for a period of one year from the date of shipment, except that
in the case of certain components, if any, listed in Section I of this operating
manual, the warranty shall be for the specified period. Hewlett-Packard will, at
its option, repair or replace products which prove to be defective during the
warranty period provided they are returned to Hewlett-Packard, and provided
the proper preventive maintenance procedures as listed in this manual are
followed. Repairs necessitated by misuse of the product are not covered by this
warranty. NO OTHER WARRANTIES ARE EXPRESSED OR IMPLIED,
INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
HEWLETT-PACKARD IS NOT LIABLE FOR CONSEQUENTIAL DAMAGES.
If this product is sold as part of a Hewlett-Packard integrated instrument
system, the above warranty shall not be applicable, and this product shall be
covered only by the system warranty.
Service contracts or customer assistance agreements are available for
Hewlett-Packard products.
For any assistance, contact your nearest Hewlett-Packard Sales and Service
Office. Addresses are provided at the back of this manual.

Model 333A/334A Section I
SECTION |
GENERAL INFORMATION
1-1. DESCRIPTION.
1-2. The Hewlett-Packard Models 333A and 334A
Distortion Analyzers are solid state instruments for
measuring distortion on ac voltages. The Models
333A and 334A include two control loops that auto-
matically tune both legs of a bridge circuit which re-
jects the fundamental when the rejection circuit is
initially set within the range of the loops. The 334A
has a high impedance detector which operates from
550 kHz to greater than 65 MHz and provides the ca-
pability of monitoring the distortion of the amplitude
modulation on an rf carrier.
1-3. Distortion levels of 0. 1% to 100% full scale are
measured in seven ranges for any fundamental frequen-
cy of 5 Hz to 600 KHz. Harmonics are indicated upto
3 MHz. The high sensitivity of these instruments re-
quires only 0. 3V rms for the 100% set level reference.
The distortion characteristics can be monitored atthe
OUTPUT connectors with an oscilloscope, a true rms
voltmeter, ог a wave analyzer. The instruments are
capable of an isolation voltage of 400 volts above
chassis ground.
1-4. The voltmeter can be used separately for general
purpose voltage and gain measurements. It has a
frequency range of b Hz to 3 MHz (20 Hz to 500 kHz
for 300 uV range) and а voltage range of 300uV to
300 V rms full scale,
1-5. The AM detector included in the Model 334A is
a broadband дс restoring peak detector consisting of
@ semiconductor diode and filter circuit. AM distor-
. tion levels as low as 0. 3% can be measured on a 3 V
to8 V rms carrier modulated 30% in the standard
broadcast band. Distortion less than 1% can be
measured at the same level of the carrier up to 65 Mc.
Table 1-1.
MODEL 333A
DISTORTION MEASUREMENT RANGE
Any fundamental frequency, 5 Hz to 600 kHz.
Distortion levels of 0. 1964-1009 are measured
full scale in 7 ranges.
DISTORTION MEASUREMENT ACCURACY
Harmonic measurement accuracy (full scale)
Fundamental Input Less Than 30 V
100%-0. 3%
0.1%
1-6. ACCESSORY FEATURES.
1-7. The accessory available with the 333A and334A
Distortion Analyzers is a voltage divider probe, -hp-
Model Ко. 10001A. The features of the probe are:
a. 10 megohms shunted by 10 pF, giving 10:1
attenuation.
b, DC to 30 MHz bandwidth.
2% division accuracy.
d. 600 V peak input.
e. 5 ns rise-time.
1-8. OPTION.
1-9, Option 01іѕа standard -hp- Model 333A or 334A
with a special meter and meter amplifier, compen-
sated to permit response to VU (volume units)
characteristics.
1-10 INSTRUMENT IDENTICATION.
1-11. Hewlett-Packard uses a two-section serial
number. The first section (prefix) identifies a series
of instruments. The last section (suffix) identifies a
particular instrument within the series. На letter is
included with the serial number, it identifies the coun-
try in which the instrument was manufactured. Н the
Serial prefix of your instrument differs from the one
on the title page of this manual, a change sheet will
be supplied to make this manual compatable with new -
er instruments or the backdating information in Арреп-
dix C will adapt this manual to earlier instruments.
All correspondence with Hewlett-Packard should in-
clude the complete serial number.
Specifications
Fundamental Input Greater Than 30 V
100%-0. 3%
10 На
300 ЕН?
30 Hz
300 ЕН?
10 Hz
3 MHz
10 Hz
1.2 MHz
0.1%
Elimination Characteristics:
Fundamental Rejection > 80 dB
Second Harmonic Accuracy for a
fundamental of:
5 Hz to 20 Hz: better than +1 dB
20 Hz to 20 kHz: better than «0. 6 dB
20 kHz to 100 kHz: better than -1 dB
100 kHz to 300 kHz: better than -2 dB
300 kHz to 600 kHz: better than -3 dB
1-1

Section I Model 333A/334A
Table 1-1. Specifications (Cont'd)
Distortion Introduced by Instrument:
> -70 АВ from 5 Hz to 200 kHz
> -64 dB from 200 kHz to 600 kHz
Meter indication is proportional to the aver-
age value of a waveform.
FREQUENCY CALIBRATION ACCURACY
Better than +5% from 5 Hz to 300 kHz
Better than: 1096 from 300 kHz to 600 kHz
INPUT IMPEDANCE
Distortion Mode: 1 МО +5% shunted by «70 pF.
Voltmeter Mode:
1 МО +5% shunted by «30 pF (333A only),
1 MQ +5% shunted by «35 pF (334A only),
1 to 300 V ranges; 1 МО +5% shunted by «70 pF,
300 u V to 0.3 V ranges.
INPUT LEVEL FOR DISTORTION MEASUREMENTS
0.3 V rms for 100% set level (up to 300 V may
be attenuated to set level reference). The
minimum measurable distortion for floating
operation on the X1 frequency range is 50dB
below the fundamental.
DC ISOLATION
Signal ground may be +400 Vdc from external
chassis,
VOLTMETER RANGE
300 рУ to 300 V rms full scale (13 ranges),
10 dB per range.
VOLTMETER FREQUENCY RANGE
5 Hz to 3 MHz (300 uV range: 20 Hz-500 kHz).
VOLTMETER ACCURACY:
20 Hz-500 kHz
5 Hz-3 MHz
5 Hz-500 kHz
30 Hz-300 kHz
lmV-30V 1 10 Hz-i MHz
100 V-300 V | 10 Hz-300 kHz
300 ру
MODEL 334A
Same as Model 333A except as indicated below:
AM DETECTOR
High impedance dc restoring peak detector with
semi-conductor diode operates from 550kHz to
greater than 65 MHz. Broadband input.
Maximum input; 40 V p-p ac or 40 V peak
transient.
. CARRIER FREQUENCY
550kHzto 1.6 MHz: Distortion introduced by
detector is « 0. 3% for 3 to 8 volt carriers
modulated 30%.
i-2
NOISE MEASUREMENTS
Voltmeter residual noise on the 300 pV range:
« 25 u V rms terminated in shielded 6000; «30
u V rms terminated in shielded 100 КО.
OUTPUT
For input frequencies from 20 Hz to 600 kHz,
0.1 V rms + 0.01 V open circuit for full scale
meter deflection; 0,05 V rms + 0.005 V into
2 КО for full scale meter deflection.
AUTOMATIC NULLING MODE
Set Level: At least 0,2 V rms.
Frequency Ranges:
X1, manual null tuned to less than 3% of set
level; total frequency hold-in +0. 5% about
true manual null.
X10 through ХОК, manual null tuned to
less than 1090 of set level;totalfrequency
hold-in +1% about true manual null,
AUTOMATIC NULL ACCURACY
5 Hz to 100 Hz: Meter reading within 0 to +3
dB of manual null.
100 Hz to 600 kHz: Meter reading within 0 to
+1.5 dB of manual null.
HIGH-PASS FILTER
3 dB point at 400 Hz with 18 dB per octave roli
off. 60 Hz rejection > 40 dB. Normally used
only with fundamental frequencies greater than
1 kHz.
POWER SUPPLY
100 v/120 V/220 V/240 V + 5% = 10%, 48 -
66 Hz, approximately 4 watts.
1.6 MHz to 65 MHz: Distortion introduced by
detector is < 1% for 3 to 8 volts rms carriers
modulated 30%.
NOTE
Distortion measurement at carrier levels
as low as i volt may be made with reduced
accuracy.
OPTION: 01
Indicating meter has VU characteristics con-
forming to FCC Requirements for AM, FM,
and TV broadcasting.

Model 333А /334А
Section П
SECTION И
INSTALLATION
2-1. INTRODUCTION.
2-2. This section contains information and instruc-
tions necessary forthe installation and shipping of the
Models 333A/334A Distortion Analyzers. Included
are initial inspection procedures, power and grounding
requirements, installation information, and instruc-
tions for repackaging for shipment.
2-3. INSPECTION.
2-4, This instrument was carefully inspected both
mechanically and electrically before shipment. It
shouldbe physically free of mars or scratches and in
perfect electrical order upon receipt. To confirm
this, the instrument should be inspected for physical
damage intransit. Also checkfor supplied accessories,
and test the electrical performance of the instrument
using the procedure outlined in Paragraph 5-5. If
there is damage or deficiency, see the warranty on the
inside front cover of this manual.
2-5. POWER REQUIREMENTS.
2-6. The Model 333A/334A can be operated from any
ac source of 100 V/120 V/220 V/240 V + 5% - 10%,
48 - 66 Hz. With the instrument disconnected from
the ac power source, move the slide (located on the
rear panel) until the desired line voltage appears.
Power dissipation is approximately 4 watts.
2-7. THREE-CONDUCTOR POWER CABLE.
2-8. То protect operating personnel, the National
Electrical Manufacturers’ Association (NEMA) recom-
тепа that the instrument panel and cabinet be grounded.
АП Hewlett-Packard instruments are equipped with a
three-conductor power cable, which, when plugged in-
toanappropriate receptacle, grounds the instrument.
The offset pin on the power cable three-prong connec =
tor is the ground wire.
2-9 INSTALLATION.
2-10. The Model 333A/334A is fully transistorized;
therefore, no special cooling is required. However,
the instrument should not be gperated where the am-
bient temperature exceeds 55° C (131 Е).
2-11. BENCH INSTALLATION,
2-12. The Model 333A/334A is shipped with plastic
feet and tilt stand in place, ready for use as a bench
instrument.
2-13. RACK INSTALLATION,
2-14. The Model 333A/334A may be rack mounted by
using the 5" RackMount Kit (-hp- Part No. 5060-0775).
Instructions for the conversion are included with the
kit.
The
rack
mount
for
the
Model
333A/334A
is
an
EIA
standard
width
of
19
inches.
When
mounted
in
à
rack
using
the
rack
mount
kit,
additional
support
at
the
rear
of
the
instrument
should
be
provided
if
vibra-
tion or similar stress is likely.
2-15. REPACKAGING FOR SHIPMENT.
2-16. The following paragraphs contain a general guide
for
repackaging
of
the
instrument
for
shipment,
Refer
to Paragraph 2-17 if the original container is to be
used;
2-18
if
it
is
not.
If
you
have
any
questions,
con-
tact your local - hp - Sales and Service Office. (See
Appendix B for office locations.)
NOTE
Ц the instrument is to be shipped to
Hewlett-Packardfor service or repair,
attachatag to the instrument identify -
ing the owner and indicate the service
orrepairto be accomplished. Include
the model number and full serial num-
ber of the instrument. In any corres-
pondence, identify the instrument by
model number, serial number, and
serial number prefix.
2-17. If original container is to be used, proceed as
follows:
а, Place instrument in original container if avail-
able. Н original container is not available, a suitable
one can be purchased from your nearest -hp- Sales
and Service Office.
b. Ensurethat container is well sealed with strong
{аре or metal bands.
2-18. If original container is not to be used, proceed
as follows:
a. Wrap instrument in heavy paper or plastic be-
fore placing in an inner container.
b. Place packing material around all sides of in-
strument and protect panelface with cardboard strips.
c. Place instrument and inner container in a heavy
carton
or
wooden
box
and
seal
with
strong
tape
or
metal bands.
d. Mark shipping container with "DELICATE
INSTRUMENT, " "FRAGILE, " etc.
2-1

Section Ш
пеене RE DETECTOR
MAX INPUT VOLTAGE 40 VOLT P-P AC
OR 40 VOLT PEAK TRARSENT
333A/2544-C-Q3854
j 334A ONLY
LINE switch turns instrument ac power on.
Pilot lamp glows when instrument is turned ON.
(2)Meter indicates distortion or voltage level of
input.
(3) море switch selects MANUAL or AUTOMATIC
bridge tuning operation.
(4) FREQUENCY RANGE switch selects frequency
range which corresponds to fundamental of input
signal.
(5)COARSE BALANCE control provides coarse ad-
justment for balancing the Wien bridge circuit.
(6) FINE BALANCE control provides a vernier ad-
justment for balancing the Wien bridge circuit.
(1) Frequency dial tunes the Wien bridge circuit to
fundamental of input signal.
(8) HIGH PASS FILTER switch inserts or bypasses
HIGH PASS FILTER in SET LEVEL and DIS-
TORTION function. When inserted, filter pro-
vides > 40 dB attenuation to 50 - 60 Hz hum
components but no attenuation to frequencies
over 1 kHz.
OUTPUT connectors provide means of monitor-
ing output of meter circuit.
(10) Frequency vernier provides fine adjustment of
frequency dial.
METER RANGE switch selects full scale range
of meter in percent, dB and rms volts.
Model 333A/334A
METERS JANGE
547 LEVES
CAUTION!
(12)sENSITIVITY selector provides 0 - 50 dB attenu-
ation of input signal in 10 dB steps in SET LEVEL
and DISTORTION functions.
(IS)SENSITIVITY VERNIER control provides fine
adjustment of sensitivity setting.
Mechanical zero adjust provides mechanical
zero adjustment of meter.
FUNCTION switch selects type of operation of
instrument.
(16) shorting bar connects circuit ground to chassis
ground.
INPUT terminals provide connections for input
signal.
(18) NORM RF DET (Model 334A only) selects front
panel INPUT or rear panel RF INPUT connector.
(9) RF INPUT connector (Model 334A only) provides
input connection for AM RF carrier input signal.
FUSE provides current overload protection for
instrument circuits.
(21) Line voltage switch sets instrument to
operate from 100 V/120 V/220 V/240 V.
(22) Ac power connector provides input connection
for ac power.
Figure 3-1. Front and Rear Panel Description
3-0

Model 333A/334A
Section ПІ
SECTION ІП
OPERATING
3-1. INTRODUCTION.
3-2. The Models 333A and 334A Distortion Analyzers
measure total harmonic distortion of fundamental fre-
quencies from 5 Hz to 600 kHz; harmonics upto 3 MHz
are included. The sharp elimination characteristics
(>80 dB), the low level of instrument induced distor-
tion, and the meter accuracy of these instruments re-
sult in highly accurate measurement of low level har-
monic distortion,
3-3. Anrms calibrated voltmeter is inherent in the
333A and 334A. The voltmeter provides a full scale
sensitivity of 300 и volts rms (residual noise «254 volts).
The voltmeter frequency range is from 5 Hz to 3 MHz
except on the 0, 0003 volt range, which is from 20 Hz
to 500 kHz.
3-4. CONTROLS AND INDICATORS.
. 8-5. Figure 3-1 illustrates and describes the function
' of all front and rear panel controls, connectors, and
indicators, The description of each component is
keyed to the drawing included within the figure.
3-6.GENERAL OPERATING INFORMATION.
3-7, INPUT CONNECTIONS.
3-8. The input signal can be connected to the 333A
and 334A through twisted pair leads or a shielded cable
with banana plug connectors. Keep all test leads as
short as possible to avoid extraneous pickup from
stray ac fields. When measuring Low-level signals,
ground loops may occur causing erroneous readings.
Ground loops may be avoided by connecting the 333A/
334A Distortion Analyzer to an appropriate isolation
transformer to break the chassis ground from power
supply ground. Connect all other instruments to one
power strip with the three-prong connectors as close
as possible.
3-9, VOLTMETER CHARACTERISTICS,
3-10. The RMS VOLTS markings on the meter face
are basedonthe ratio betweenthe average and effective
(rms) values of a pure sine wave. The ratio of average
to effective values in a true sine wave is approximately
0.9to 1. Whenthe meter is used to measure complex
waves, the voltage indicated may not be the rms value
of the signal applied. This deviation of meter indica-
tion exists because the ratios of average to effective
values are usually not the same in a complex wave as
іп а.віпе wave. The amount of deviation depends on
the magnitude and phase relation betweenthe harmonics
and fundamental frequency of the signal applied.
Table 3-1 lists the deviation of the meter indication
of a sine wave partly distorted by harmonics. Ав in-
dicated in the table, harmonic content of less than 10%
results in very small errors.
INSTRUCTIONS
Table 3-1
Effect of Harmonics on Voltage Measurements
True Meter
RMS Value Indication
Fundamental = 100 100
Fundamental + 10% 100
2nd harmonic
Fundamental + 20%
2nd harmonic
Fundamental + 50%
2nd harmonic
Fundamental + 10%
8rd harmonic
Input Voltage
Characteristics
100 - 102
100 - 110
96 - 104
Fundamental + 20%
3rd harmonic
94 - 108
Fundamental + 50%
3rd harmonic
90 - 116
l NOTE
This chart is universal in application
since these errors are inherent in all
average-responding voltage-measuring
instruments.
3-11. When making distortion measurements where
the fundamental frequency is suppressed and the re-
mainder of the signal is measured, the reading ob-
tained on an average responding meter may deviate
irom the true total rms value. When the residual
wave contains many inharmonically related sinusoids,
the maximum error in the distortion reading is about
11 % (11 % of the measured distortion) low for dis-
tortion levels below 10 %.
EXAMPLE:
Measured Maximum Error Total
Distortion In Meter Indication Distortion
2.5% +0. 11x0. 025= 0.025+0, 0027=
0.00027 0. 0277 or 2. 8%
This example representsthe maximum possible error,
and in most cases the error is less. In distortion
measurements, the reading of an average-responding
meter is sufficiently close to the rms value to be
satisfactory for most applications.
3-12. OUTPUT TERMINALS.
3-13, The OUTPUT terminals provide a 0.1 V rms
open circuit output for full scale meter deflection.
These terminals can be used to monitor the output
signal with an oscilloscope, a true rms voltmeter, or
a wave analyzer. The combination of the distortion
meter and oscilloscope provides more significant in-
3-1

Section Ш
formation about the device under test than the
expression of distortion magnitude alone. Information
obtained from the oscilloscope pattern is specific and
reveals the nature of distortion which sometimes
occurs at such low levels that it is difficult to detect
in the presence of hum and noise. The impedance at
the OUTPUT terminals is 2000 ohms, therefore, ca-
pacitive loads greater than 50 pF should be avoided
to maintain the accuracy of meter readings.
3-14. OPERATING PROCEDURES.
3-15. INSTRUMENT TURN-ON.
a. Setthe 115-230 VAC switch to coincide with the
line voltage in use. Turn switch to ON position.
Pilot lamp willglow, indicating application of
primary power.
3-16. ADJUSTMENT OF METER MECHANICAL
ZERO.
3-17. The meter is properly zero-set when the
pointer rests over the zero calibration mark and the
instrument is in its normal operating enivronment
and is turned off. Zero-set the meter as follows to
obtain maximum accuracy and mechanical stability:
a, Turn instrument on and allow it to operate
for at least 20 minutes, to let meter move-
ment reach normal operating temperature.
b. Turn instrument off and allow 30 seconds
for all capacitors to discharge.
c. Rotate zero adjustment screw clockwise un-
ti! pointer isleft of Zero and moving upscale.
d. Continue rotating screw clockwise; stop when
pointer is exactly at zero.
e, When pointer is exactly over zero, rotate
adjustment screw slightly counterclockwise
to relieve tension on pointer suspension. 1f
pointer moves offzero, repeat steps c through
е, but make counterclockwise rotation less.
3-18. DISTORTION MEASUREMENT.
CAUTION?
DO NOT EXCEED THE INPUT VOLT-
AGES LISTED BELOW TO PREVENT
DAMAGING COMPONENTS ON À2
BOARD.
VOLTMETER FUNCTION -1V
RANGE AND BELOW, AND
-DISTORTION ANALYZER 575
FUNCTION - MAXIMUM
SENSITIVITY.
1. 800 V ABOVE 100 Hz
2. 50 V ABOVE 1 kHz
3-19. MANUAL MODE.
a. Turn instrument on and mechanically zero
meter according to procedure in Paragraphs
3-15 and 3-16,
3-2
Model 333A/334A
Set NORM-R. F. DET. switch to NORM.
Set FUNCTION switch to ЗЕТ LEVEL.
Set MODE switch to MANUAL,
If fundamental frequency is 1kHz or greater,
set HIGH PASS FILTER switch to IN,
Set SENSITIVITY selector to MIN. position,
and rotate VERNIER control maximum
counterclockwise.
NOTE
The bandwidth of the SENSI-
TIVITY selector is reduced
in the two extreme CCW
positions (positions used with
an input signal greater than
30 V).
Set METER RANGE switch tó SET LEVEL,
and set BALANCE COARSE and FINE con-
trols to center position.
Connect signal to be measuredto 333A/334A
INPUT terminals.
WARNING В
REMOVE SHORTING STRAP BETWEEN
FRAME GROUND (4) AND CHASSIS
GROUND ( у ) TERMINALS ON FRONT
PANEL INPUT TERMINALS WHEN
MEASURING DISTORTION BETWEEN
TWO POINTS WHICH ARE DC OF FSET
FROM GROUND POTENTIAL.
Set SENSITIVITY selector to obtain meter
indication greater than 1/3 full scale.
Adjust SENSITIVITY VERNIER for full scale
meter indication if making distortion measure-
ment in percent; if making distortion measure-
ment in dB adjust SENSITIVITY VERNIER
for 0 dB meter indication.
NOTE
If unable to adjust for full scale
or 0dB indication, (which indicates
input signal is below 0.3 volts),
set METER RANGE selector down-
scale. Use this new setting as the
1000 ог 0dB SET LEVEL position,
thus making the next range 3090
or -10 dB, etc.
Set FREQUENCY RANGE switch and frequency
dial to fundamental frequency of input signal.
Set FUNCTION switch to DISTORTION,
Adjust frequency dial vernier and BALANCE
COARSE and FINE controls for minimum

Model
333A/334A
Section
III
n.
p.
meter
indication.
Set
METERRANGE
switch
3-21.
DISTORTION
MEASUREMENT
OF
АМ
RF
down-scale
as
necessary
to
keep
meter
in-
CARRIERS
(334A
only).
dication
on
scale.
"rV
Repeat
step
m
until
no
further
reduction
in
meter
indication
can
be
obtained.
DO NOT EXCEED MAXIMUM INPUT
я ) it З 4
Observe
distortion
either
in
percentage
or
VOLTAGES
LISTED
ON
REAR
PANEL.
dB, as indicated by meter deflection and
METER RANGE switch setting. For example,
if
meter
indicates
0.4
and
METER
RANGE
a.
Turn
instrument
on
and
mechanically
zero
setting
is
1%,
distortion
measured
is
0.4%
meter
according
to
procedure
in
Paragraphs
of
fundamental.
Similarly,
if
meter
indi-
3-15
and
3-16.
cates
-6
dB
and
METER
RANGE
setting
is
-40
dB,
distortion
measured
is
-46
dB
from
b.
Set
NORM.-R.F.
DET.
switch
to
R.
F.
DET.
fundamental.
c. Connect input signalto R. Е. INPUT terminal
on rear panel.
SUUS
d.
Refer
to
Paragraph
3-19
for
manual
distort-
In
MANUAL
mode
the
accuracy
ion
measurement;
refer
to
Paragraph
3-20
of
distortion
measurements
is
for
automatic
distortion
measurement.
affected
by
frequency
stability
of
the
input
signal,
An
inaccuracy
——
NOTE
in
distortion
indications
occurs
when
the
frequency
drift
of
the
If
no
meter
deflection
can
be
input
signal
exceeds
the
bandwidth
obtained
with
an
RF
input,
diode
ACRI should be checked. А
spare diode is located on the
outside of the A4 shield.
of the rejection curve.
If desired, rms voltage of input signal can
be
measured
by
setting
FUNCTION
switch
to
3-22.
VOLTAGE
MEASUREMENT.
VOLTMETER, and setting METER RANGE
switch
to
obtain
an
on-scale
indication.
a.
Turn
instrument
on
and
mechanically
zero
meteraccordingto
procedure
in Paragraphs
3-15
and
3-16,
3-20. AUTOMATIC MODE.
Ce
d.
| Et (
Perform
steps
athroughlof
Paragraph
3-19.
b.
Set
NORM.-R.
F.
DET.
switch
to
NORM,
i та
Adjust
frequency
dial
vernier
and
BALANCE
c.
Set
FUNCTION
switch
to
VOLTMETER.
COARSE
and
FINE
controls
for
minimum
d.
Set
METER
RANGE
switch
to
a
range
meter
indication.
exceeding
amplitude
of
signal
to
be
mea-
sured.
When meter indication is less than 10% of
SET
LEVEL
indication,
set
MODE
switch
to
е,
Connect
signal
to
be
measured
to
INPUT
AUTOMATIC.
(Н
fundamental
cannot
be
terminals.
manually nulled below 10% of SET LEVEL
indication,
automatic
mode
cannot
be
used).
f.
Set
METER
RANGE
switch
to
give
a
reading
as
close
to
full
scale
as possible,
and
00-
Set
METER
RANGE
switch
down-scale
to
serve
meter
indication.
obtain on-scale meter indication.
g.
The
dB
scale
of
the
333A/334A
is
calibrated
Observe
distortion
either
in
percentage
or
in
dBm,
such
that
0
dBm
=
1
milliwatt
dissi-
dB,
as
indicated
by
meter
deflection
and
pated
by
600
ohms.
Therefore,
a
dBm
mea-
METER
RANGE
switch
setting.
For
example,
surement
must
be
made
across
600
ohms.
if
meter
indicates
0.4
and
METER
RANGE
However,
dB
measurements
across
other
setting
is
10,
distortion
measured
is
0.
4%
impedances
can
be
converted
to
dBm
by
use
of
fundamental.
Similarly,
if
meter
indicates
of
the
Impedance
Correction
Graph
of
Fig-
-6
dB
and
METER
RANGE
setting
is
-40
dB,
ure
3-3.
For
example:
to
convert
a
-30
dB
distortion
measured
is
-46
dB
from
funda-
reading
across
200
ohms
to
dBm,
locate
the
mental.
200
ohm
impedance
line
at
the
bottom
of
the
graph.
Follow
the
impedance
line
to
the
If
desired,
rms
voltage
of
input
signal
can
be
heavy
black
line,
and
read
the
meter
correc-
measured
by
setting
FUNCTION
switch
to
tion
at
that
point.
The
correction
for
200
VOLTMETER,
and
setting
METER
RANGE
ohms
is
+5
dBm;
thus
the
corrected
reading
switch
to
obtain
an
on-scale
indication.
is
-25
dBm.
3-3

Section Ш
3-23, METER INDICATION.
3-24. The 333A/334A meter is calibrated to indicate
in both dB and volts. It is interesting to notethat the
METER RANGE markings differ from most ac volt-
meter range markings. On most ac voltmeters (600
ohms) 0 dB corresponds to the 1 volt range. This is
not true inthe case of the 333A/334A. Since the instru-
ment is primarily a distortion analyzer, measurements
are in dB (relative measurement) rather than in dBm
(absolute measurement). Zero dB оп the 333A/334A
corresponds to 0.3 volt range rather than the 1 volt
range. This allows 210 dB greater dynamic range of
distortion measurements.
3-25. If measurements are to be made in dBm, 10 dB
must be subtracted from the METER RANGE setting.
Thus 0 dB becomes the -10 dBm range for absolute
power measurements. Zero dBm is equal to 1 milli-
watt dissipated by any impedance andinthis particular
case is 600 ohms. The «10 DECIBELS marking on the
meter face indicates that when voltmeter measurements
are being made, the indication (METER RANGE plus
meter indication) is 10 dB greater than when power
(dBm) measurements are being made.
3-26. In short, when distortion and voltage measure-
ments are being made, utilizethe instrument METER
RANGE and meter scale as they exist. For absolute
power measurements in dBm, simply subtract 10 dB
from the METER RANGE setting.
3-27. USE OF OUTPUT TERMINALS.
3-28. In VOLTMETER and SET LEVEL functions, the
333A/334A can be used as a low distortion, wide-band
amplifier. А portion of the meter input (0.1 V rms
open circuit forfullscale meter deflection is provided
at the OUTPUT terminals.
3-29. In DISTORTION function, the distortion (0.1 V
rms open circuit forfull scale deflection) is provided
atthe OUTPUT terminals for monitoring purposes.
NOTE
The INPUT Y terminal and the
OUTPUT d terminal shouldnot be
connected directly together when
making low level measurements.
These terminals are isolated from
each other by 1 ohm which reduces
the effects of common mode voltages.
Model 333A /334А
3-30. 333A/334A WITH OPTION 01.
3-31. Operating procedures for the 333A/334A with
OptionOlarethe same asforthe standard instrument.
The only difference between the standard and optional
instrument is that the Option 01 has a special meter
and meter amplifier whichis compensated to respond
to VU (volume unit) characteristics. |
3-32. MANUAL NULLING.
3-33. Since the frequency and balance controls are
rather sensitive in the MANUAL mode, the following
information is suppliedto simplify nulling the
333A/334A іп the MANUAL mode, When nulling the
3334/3344 in the MANUAL mode, connect the equip-
ment as shown below and adjust the 333A/334A fre-
quency and balance controls for the waveform shown
in step a below, Additional waveforms are provided
to simplify nulling.
а. www No harmonic distortion, Frequency
and balance adjustment correct,
b. 7 Frequency and balance control im-
properly adjusted,
с. Frequency approximately correct;
balance incorrect.
d. CLLD Balance approximately correct; fre-
quency incorrect,
e. COX 2 Second harmonie predominant; fre-
quency and balance adjusted,
f. --77---. Second harmonie predominant; fre-
quency and balance adjusted; phase
changed.
ge 7“-----” Second harmonic predominant; fre-
quency and balance adjusted; phase
changed,
һ CXX Third harmonic predominant.
i. n 2 pee incorrect; meter reading off
Scale.
h P AE. Frequency incorrect; meter reading
off scale.

Model 333А/334А
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METER CORRECTION - DBM
Se Se
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FM vem PPAR ИН ae a RICOTTA NLL mnm ttbi KG rA
Figure 8-3.
OSCILLOSCOPE
DISTORTION. ANALYZER
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Section TIT
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Model 333A/334A
Section IV
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Model 333A/334A
SECTION
THEORY OF
4-1. OVERALL DESCRIPTION.
4-2. Models 333A and 334A Distortion Analyzers in-
clude an impedance converter, a rejection amplifier,
a metering circuit, and a power supply. The Model
334A also contains an AM detector, The impedance
converter provides a low noise input circuit with a
high input impedance independent of source impedance
placed
at
the
INPUT
terminals.
The
rejection
ampli-
fier
rejects
the
fundamental
frequency
of
the
input
signal
and
passes
the
remaining
frequency
components
on to the metering circuit for measuring distortion.
The metering circuit provides visual indications of
distortion and voltage levels on the front panel meter,
M1. The AM detector (Model 334A only) detects the
modulating signal from the RF carrier and filters all
RF
components
from
the
modulating
signal
before
it
is applied to the impedance converter circuit.
4-3. BLOCK DIAGRAM DESCRIPTION.
(Refer to Figure 4-1)
4-4. DISTORTION MEASURING OPERATION.
4-5. For distortion measurement, the input signalis
applied to the impedance converter (Assembly А2)
through the FUNCTION selector, S1, and the one
megohm attenuator. The one megohm attenuator is a
voltage divider network which provides 50 dB atten-
uation in 10 dB steps. The desired level of attenuation
is selected by the SENSITIVITY selector, 62. The
impedance converter provides impedance matching and
unity gain between the INPUT terminals and the input
of the rejection amplifier.
4-6.
Therejectionamplifier
consists
of
a
preamplifier,
a
Wien
bridge,
andabridge
amplifier,
The
SENSITIVITY
VERNIER
control,
at
the
input
of
the
preamplifier,
provides
a
set
level
signal
to
obtain
a
full
scale
read-
ing
on
the
meter
for
any
voltage
level
at
the
input
of
the
instrument.
With
the
FUNCTION
switch
inthe
SET
LEVEL
position,
a
ground
is
applied
to
the
Wien
bridge
circuit
to
allow
a
signal
reference
level
to
be
set
up
on
the
meter.
With
the
FUNCTION
switch
in
the
DIS-
TORTION
position,
the
Wien
bridge
is
used
as
an
in-
terstage
coupling
network
between
the
preamplifier
and
bridge
amplifier.
The
Wien
bridge
is
then
tuned
and
balanced
to
reject
the
fundamental
frequency
of
the
applied
input
signal,
Two
automatic
control
loops
con-
sisting
of
two
phase
detectors,
lamp
drivers,
lamps,
and
photocells
provide
fine
tuning
and
balance
in
the
AUTOMATIC
MODE.
The
remaining
frequency
com-
ponents
are
applied
to
the
bridge
amplifier
and
are
measured
as
distortion
by
the
metering
circuit.
Nega-
tive
feedback
from
the
bridge
amplifier
to
the
preamp-
lifier
narrows
the
rejection
response
of
the
Wien
bridge.
4-7, The output of the rejection amplifier is applied
to the metering circuit through the post-attenuator.
The post-attenuator is used to limit the input signal
Section IV
iV
OPERATION
level applied to the metering circuit to 1 mV for full
Scale deflection. Sensitivity of the metering circuit
is increased to 300 uV for full scale deflection onthe
.0003V range. The metering circuit provides a visual
indication of the distortion level of the input signal.
In addition tothe indication provided by the meter, the
OUTPUT terminals provide a means of monitoring
the distortion components.
4-8. DISTORTION MEASUREMENT IN AM
CARRIERS.
По
4-9, The Model 334A Distortion Analyzer contains an
AM detector circuitfor measuring envelope distortion
in AM carriers, The input signal is applied to the in-
put of the AM detector circuit where the modulating
signal is recovered from the RF carrier. The signal
is then applied to the impedance converter circuit
through the one megohm attenuator and then through
the same circuits previously described in the distor-
tion measuring mode operation.
4-10. VOLTMETER OPERATION.
4-11. Inthe voltmeter mode of operation, the input
signal is applied to the impedance converter circuit
through the 1:1 and 1000:1 attenuator. The 1:1 atten-
uation ratio is used onthe 0, 0003 100. 3 VOLTS ranges,
and the 1000:1 attenuation ratio is used in the 1 to 300
VOLTS
ranges.
With
the
FUNCTION
switch
in
the
VOLTMETER
position,
the
output
of
the
impedance
converter bypasses the rejection amplifier and is
applied to the metering circuit through the post-
attenuator (METER RANGE switch). Metering circuit
sensitivity is increased from 1 mV for full scale
deflection
to
300
u
V
on
the
,
0003V
range,
as
it
was
in
the distortion measuring operation. The function of
the post-attenuator and metering circuit is the same for
voltmeter operation as for the distortion measuring
operation.
4-12.
DETAILED CIRCUIT DESCRIPTION.
4-13. IMPEDANCE CONVERTER CIRCUIT.
(Refer to Figure 7-2)
4-14, The input signal is applied to the impedance
converter
circuit
through
the
1:1
and
1000:1
attenuator
S3R12
in
voltmeter
operation,
and
through
the
one
megohm
attenuator
S2R1
through
S2R6
in
distortion
operation.
Capacitive
dividers
S2C1
through
52С10
in the attenuator keep the frequency response flat.
The impedance converter is a low distortion, high
input impedance amplifier circuit with gain indepen-
dent of the source impedance placed at the INPUT
terminals,
4-15. Instrument induced distortion of the signal
being measured is minimized by keeping the input
impedance and the gain of the impedance converter
4-1

Section IV
linear. The input impedance is kept linear by use of
local positive feedback from the source of A2Q1 to
the gate of А201 and to the protective diodes A2CR2
and A2CR3. Thus signals with a large source imped-
ance can be measured accurately. Overall induced
distortion is further minimized by а high open loop
gain and 100% negative feedback. The high open loop
gain is achieved by local positive feedback from the
emitter of A2Q3 to the collector of A2Q2. Overall
negative feedback from the emitter circuit of A2Q4
to the source of A2Q1 results in unity gain from the
impedance converter.
4-16. Thebias points of thetransistors in the imped-
ance converter are selected to minimize instrument
induced distortion. A2Q1, an extremely low noise,
high impedance field effect transistor, is the major
component that makes linearity of the impedance con-
verter independent of the signal source impedance.
4-17. REJECTION AMPLIFIER CIRCUIT.
(Refer to Figures 7-3 and 7-5)
4-18. The rejection amplifier circuit consists of the
preamplifier (A3Q1 thru A3Q3), the Wien bridge
resistive leg and auto control loop (А501 thru A5Q9
with associated lamp and photocell) the reactiveleg
and auto control loop (A5Q10 thru A5Q18 with associ-
ated lamp and photocell), and the bridge amplifier
(A3Q4 thru A3Q6).
4-19. PREAMPLIFIER CIRCUIT.
4-20. The signal from the impedance converter is
applied to the preamplifier, which is used during SET
LEVEL and DISTORTION measuring operations,
Negative feedback from the junction of АЗВ10 and
АЗК1 is applied to the junction of A3R2 and АЗС? to
establish the operating point for A3Ql. Negative
feedback from the emitter of A3Q3 is applied to the
emitter of A3Q1 to stabilize the preamplifier. The
preamplifier, like the impedance converter, is
designed for high open loop gain and low closed loop
gain to minimize instrument induced distortion,
4-21. WIEN BRIDGE CIRCUIT.
4-22. Inthe distortion measuring operationthe Wien
bridge circuit is used as a rejection filter for the
fundamental frequency of the input signal. With the
FUNCTION selector, S1, inthe DISTORTION position,
the Wien bridge is connected as an interstage coupling
network between the preamplifier circuit and the
bridge amplifier circuit. The bridge is tuned to the
fundamental frequency of the input signal by setting
the FREQUENCY RANGE selector, S4, for the appli-
cable frequency range, andtuning the capacitors C4A
through C4D. The bridge circuit is balanced by ad-
justing the COARSE balance control, R4, andthe FINE
balance control, R5. In the AUTOMATIC MODE fine
tuning and balancing are accomplished by photoelectric
cells which are in the resistive and reactive legs of
the Wien bridge. The error signals for driving the
photocells are derived by detecting the bridge output
using the input signal as a reference.
4-23, When the Wien bridge is not tuned exactly to
the frequency tobe nulled, a portion of the fundamental
4-2
Model 333A/334A
iNPUT TO BRIDGE A
OUTPUT OF BRIDGE
iF RESISTIVE LEG B
15 UNBALANCED
OUTPUT OF BRIDGE
IF REACTIVE LEG С
15 DETUNED
ЗЗЗА-8-1464
Figure 4-2, Bridge Waveforms
frequency will appear at the bridge output. The phase
of this signal depends on which leg of the bridge is not
tuned, or on the relative errors in tuning if neither is
set correctly. The magnitude of the signal is propor-
tional to the magnitude of the tuning error of either or
both legs of the bridge. l
4-24, Figure 4-2a shows a sinusoid input tothe Wien
bridge. If the resistive leg of the bridge is slightly
unbalanced, the output of the bridge is very small,
but has the waveform shown in Figure 4-2b and is in
phase with the input. As the resistive leg is tuned,
the signal approaches zero amplitude at null and then
becomes larger, but 180° out of phase, if the null
position is passed, Whenthe resistive leg is correctly
tuned and the reactive leg is tuned through null, a
Similar waveform is produced, Figure 4-2c. The
only difference is that the reactive signal is 909 out
of phase with the resistive signal.
4-25. When the bridge output is detected using the
input signal as the reference, the error signals in
phase or 1809 out of phase with the reference develop
a voltage that is used to vary the resistance in the
resistive leg of the bridge, to tune it to the correct
null position. Signals of the form in Figure 4-2c do not
develop any voltage, as the resistive detector is in-
sensitive to inputs differing from the reference by 900.

Model 333A/334A
TYPICAL WIEN BRIDGE
bc
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Section ТУ
Шет ТЕДІ ОҒ FEEDBACK
FREQUENCY
. Figure 4-3, Wien Bridge Circuit and Rejection Characteristics
4-26. In an independent, but similar, control loop,
the bridge input signal is shifted 90° and used as the
reference signal for the detector. This detector
develops control voltages to null the reactive leg of
the bridge, but is insensitive to signals of the form
in Figure 4-2b, which are caused by small tuning
errors of the resistive branch.
4-27, The result is that the two control loops derive
information from a common source and develop two
independent control signals for nulling the two legs of
the bridge. These control voltages are used to vary
the brilliance of lamps, which in turn cause resistance
changes in photocells that form part of the Wien bridge.
4-28. When the bridge circuit is tuned and balanced,
the voltage and phase of the fundamental, which
appears at junction of the series reactive leg (S4R1,
3, 5, 7, or 9 and C4A/B) and the shunt reactive leg
(SAR11, 13, 15, 17, or 19, and C4C/D), is the same
as at the midpoint of the resistive leg (A3R12 and
A3R14), When these two voltages are equal and in
phase, the fundamental frequency will not appear at
the drain of the field effect transistor A3Q4. For
frequencies other than the fundamental, the reactive |
leg of the Wien bridge offers various degrees of
attenuation and phase shift which cause a voltage at
the output points of the bridge. This difference volt-
agebetweenthe reactive leg and resistive leg is amp-
lified by A3Q4, A3Q5, and A3Q6. Figure 4-3 illus-
trates a typical Wien bridge circuit and the rejection
characteristics for it.
4-29. The Wien bridge circuit is designed to cover a
continuous frequency range of over a decade for each
position of the FREQUENCY RANGE selector 54, 54
provides coarse tuning of the reactive leg by changing
the bridge circuit constants in five steps at 1 decade
per step. For the automatic control loop, the refer-
ence voltage is taken from R6 at the input to the re-
jection amplifier and applied to the buffer amplifier
А597. The reference voltage is amplified and clipped
by A5Q8 and А509, and coupled to the detector A5Q4.
The output of the metering circuit, which contains the
fundamental frequency if either leg of the bridge is
untuned, is applied to the buffer amplifier A5Q1.
It is amplified by A5Q2 and A5Q3 and coupled to the
detector А504,
4-30. RefertoFigure 4-4, partial schematic for
detector operation. The discussion is applicable
to both resistive and reactive detector circuits.
4-31. The signals from the error amplifier, (A5Q2
and A5Q3) will be equal and of opposite phase, and
will cancel out each other when the detector, A5Q4, is
off. However, when the positive half of the reference
square wave gates A5Q4 on, the signal from the coll-
ector of A5Q3 will be shorted to ground. Thus the
signal from the collector of A5Q2 will be coupled
through the filter network to the base of A5Q5. If the
signal from A5Q2 is in phase with the reference, the
positive half of the signal will be passed, and if it is
out of phase, the negative half will be passed.
4-32, The normal working voltage at ASTP3 is be-
tween 0 апа -1volt, The de output of the filter network
causes the voltage at ASTP3 to go in a positive direc-
tion (toward zero) for in phase error signals, and in
a negative direction (toward -1 V)for out of phase error
signals. The change in base voltage is then amplified
by A5Q5 and lamp driver А566. This will change the
brilliance of lamp А6051, which will vary the resist-
ance of A6V1 inthe direction necessary to balance the
resistive leg of the bridge.
COLLECTOR COLLECTOR
OF Q3 OF Q2
—
еле
с6
TP2
RIO
RII
COLLECTOR
CIRCUIT Q9
3334/3344 -ROR
Auto Control Loop Detector
Figure 4-4.
4-3

Section IV
4-33, Refer to Figure 4-5 for the phase relationship
of the bridge error signal andreference voltage at the
base of А594. The shaded portions of the error sig-
nals (b and c) indicate that part of the error signal
which contributes to the dc lamp control voltage. Аз
indicatedind, any error signal that is 90° out of phase
with the reference does not affect the dc lamp control
voltage, because equal amounts of the positive and
negative portions are passed.
4-34. The operation of the reactive branch control
loop is similar to that of the resistive branch, The
Ref. signalforResistive
Detector (A5Q4)
Resistive Error signal
in phase with reference
at bridge
Resistive Error signal
180° out of phase
Reactive Error signal
90° out of phase (Results
in no output from Re-
sistive Detector)
Error signal, reactive
leg detuned, resistive
leg unbalanced
333A/334A-RO
Model 333A/334A
phase delay circuit, A5Q15, A5Q16, S4AF and
S4C1 through S4C5, shifts the reference voltage
909, as shown in Figure 4-5f. This makes the detector
A5Q12 sensitive to components of the bridge error
signal that are 909 out of phase (g and h). The output
of the lamp driver, A5Q14, controls the brilliance of
A6DS2, which varies the resistance of A6V2 through
A6V5 to tune the branches of the reactive leg. Deck
AR of the FREQUENCY RANGE switch, S4, switches
А5Ң56 in parallel with A5R55 on the top three fre-
quency ranges. А6052 willbecome brighter, andlower
the resistance of A6V2 through A6V5, making variation
o 3 5°
360° | Lr
| |
|
|
1
|
1809
|
Ref. signal for Reactive
Detector (A5Q12)
|
|
|
|
|
|
|
|
|
|
Reactive Error signal
in phase with reference
at bridge
Reactive Error signal
out of phase
Resistive Error signal
90° out of phase (Results
in no output from Re-
active Detector)
Error signal, Reactive
leg detuned, Resistive
leg unbalanced
Figure 4-5, Reference and Error Phase Relationship

Model 333A/334A
BRIDGE
AMPLIFIER
А394 ~
A3Q6
WEIN
BRIDGE
NEGATIVE FEEDBACK
3334/334A-RO
Section ТУ
5 50 500 5000 50K 600K
AMPLIFIER GAIN db
FREQUENCY .
Figure 4-6. Rejection Amplifier Block Diagram and Typical Frequency Rejection Characteristic
in resistance less than on the two lower ranges. How-
ever, less variation in resistance is needed to tune
the leg, because the impedance in the reactive leg
becomes progressively less as the higher frequency
ranges are selected.
4-35. Any error signal that is not an integral multiple
of 90° is the result of the reactive leg of the bridge
being detuned, andthe resistive leg being unbalanced.
For example, an error signal that is 45° out of phase
(Figure 4-5e and j) will result in outputs from both
resistive and reactive detectors to tune the bridge
and reject the fundamental.
4-36, When the FUNCTION selector is set to the
VOLTMETER or SET LEVEL position, the junction
of the series and shunt reactive branches ofthe Wien
bridge is connected to circuit groundthrough A3R19
by SIBF which disables the frequency rejection
characteristic of the bridge circuit. With the bridge
circuit disabled, the rejection amplifier circuit pro-
vides one dB of gain for the fundamental frequency
and the harmonics. In the SET LEVEL operation, this
signal is used to establish the SET LEVEL refer-
ence.
4-37. BRIDGE AMPLIFTER CIRCUIT.
4-38, The bridge amplifier circuit consists of three
stages of amplification, A3Q4 through A3Q6. The
first stage of amplification, A3Q4, is a field effect
transistor which amplifies the difference signal between
the gate andthe source. The field effect transistor is
selected for minimum noise performance with the high
impedances of the Wien bridge circuit. The signal
from the drain is applied to the two stage feedback
amplifier A3Q5 and A3Q6. The output of A3Q6 is
coupled to the meter circuit by the post attenuator
S3R1 through S3R11. Negative feedback from the out-
put of the bridge amplifier is applied to the preamp-
lifier circuit to narrow the frequency rejection
characteristic. It can be noted from the rejection
characteristic (refer to Figure 4-3) for the bridge
that the rejection of harmonic voltages is not con-
stant. Typically the second harmonic is attenuated
several dB more than the third harmonic andthethird
more than the fourth. The result of the negative feed-
back is illustrated by the rejection characteristic
Shown in dashed lines on the attenuation and phase
characteristic of Figure 4-3, Figure 4-6 shows a
simplified block diagram of the rejection amplifier
with the typical frequency-rejection characteristic.
Refer to Figure 4-7, Bandwidth Versus Null Depth for
further detail on the rejection characteristic.
4-39. HIGH PASS FILTER.
(Refer to Figure 7-3).
4-40. The HIGH PASS FILTER is normally used when
the fundamental of the input signal is greater than 1
kHz. In the voltmeter mode of operation, the filter
is not used. In SET LEVEL and DISTORTION func-
tions the filter presents » 40 dB attenuation to 50 or
60 Hz hum components, but offers no attenuation to
frequencies over 1 kHz. The filter assembly, АТ,
consists of A7C1, АТС2, апа А711, The filter can
be inserted or bypassed by the HIGH PASS FILTER
switch, S9.
4-41. METER AMPLIFIER.
(Refer to Figure 7-4)
4-42. The meter amplifier consists of the post atten-
uator, the meter amplifier circuit, and the meter
rectifier circuit.
4-43, POST ATTENUATOR.
4-44, The post attenuator, S3R1 through S3R11, is a
resistive network which attenuates the input signal in
10 dB steps. The attenuator is usedin conjunction
with either the input sensitivity attenuator or the
1000:1 attenuator to limit the signal level to the
meter amplifier to 1 mV for full scale deflection on
all ranges from 1 mV to 300 V full scale. The meter
circuit sensitivity is increased to 300 рҮ for full
scale deflection on the .0003V range by switching
resistors A2R29 and A2R30 into the calibration net-
work. Resistor A2R41 and capacitor A2C29 are also
Switched into the calibration network on the .0003V
range to extend the passband of the amplifier.
4-45, METER AMPLIFIER CIRCUIT.
4-46, The meter amplifier circuit consists of a five
stage amplifier circuit, A2Q5 through A2Q9, which
develops the current for full scale meter deflection.
Negative dc feedback from the emitter circuit of
A2Q8 is applied to the base of А205 to stabilize the
dc operating point of the meter amplifier circuit and
to minimize the tendency for de drift due to ambient
temperature changes. A2R51 and A2CR8 are electric-
ally in the circuit only whenthe meter amplifier is over-
loaded. When the voltage on the emitter of A2Q9
4-5

Section IV Model 333A/334A
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4-6

Model 333А/334А
becomes abnormally large during anoverload, A2CR8
breaks down and provides a lower resistance charg-
ing path for А2С15, which reduces the transient re-
covery time ofthe meter amplifier. Negative ac feed-
back is applied from the collector circuit of A2Q9 to
the emitter circuit of A2Q5. This feedback is used
to ensure flat frequency response, to improve linear-
ity, and to reduce the effect of variationoftransistor
parameters with environmental changes. In this
manner, the calibration of the instrument is made
dependent on high quality passive components.
4-47, METER RECTIFIER CIRCUIT.
4-48. The meter rectifier is connected in a bridge
type configuration with a diode in each upper branch
and a dc milliammeter connected across the midpoints
of the bridge. The simplified meter rectifier is illus-
trated in Figure 4-8, The generator represented by
A2Q5 through A2Q9 with the internal impedance Ro
provides the meter, M1, with current for full scale
deflection and develops a voltage across the calibra-
tion network, which closes the ac feedback loop.
Capacitors A2C27 and A2C28 are used as coupling
capacitors for the ac feedback loop, output signal to
the OUTPUT connector, and the bridge error signal
to the input of the automatic fine tuning loops. The
mechanical inertia of the meter and A2C26 prevents
the meter from responding to individual current
pulses, Therefore, the meter indication corresponds
to the average value of the current pulses rather than
the peak value. The meter is calibrated to indicate
the rms value of a sine wave. Resistor A2R45 im-
presses a fixed bias across diodes A2CR6 and A2CR7
(biasing them close to the barrier voltage) to make the
meter amplifier response linear to large variations
LonceoccuJ
A2R34
Figure 4-8.
Section IV
in signal amplitude. The linearity of this type of cir-
cuit is also increased by including the meter circuit
in the overall feedback loop.
4-49, POWER SUPPLY CIRCUIT.
(Refer to Figure 7-6)
4-50. The power supply circuit consists of a +25 volt
series regulated supply anda -25 volt series regulated
supply which is the reference supply for the +25 volt
supply.
4-51, The -25 volt regulated supply is ofthe conven-
tional seriesregulator type. The amplifier A1Q5 is
used to increase the loop gain of the circuit, thus im-
proving voltage regulation. The positive feedback
applied to the junction of A1R11 and A1R12 is used to
further improve the line frequency suppression of the
circuit,
4-52, The +25 volt regulated supply is of the conven-
tional series regulator type and operates the same as
the -25 volt regulated supply.
4-53. RF DETECTOR CIRCUIT. (334A only)
(Refer to Figure 7-2)
4-54, The RF detector circuit consists of a rectifier,
ААСВ1, and filter circuit. The RF signal is applied
to the circuit through the RF INPUT connector onthe
rear panel. The rectifier diode A4CR1 recovers the
modulating signal from the RF carrier and the fiiter
circuit removes any RF components before the signal
is applied to the impedance converter circuit through
the NORM-RF DET switch, 87.
3334/3344- AO
Simplified Metering Circuit
4-7