HP 333A Service manual

Errata
Title & Document Type: 333A/334A Distortion Analyzer Operating & Service Manual
Manual Part Number: N/A
Revision Date: October 1985
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Hewlett-Packard's former test and measurement, semiconductor products and chemical
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this manual copy. The HP XXXX referred to in this document is now the Agilent XXXX.
For example, model number HP8648A is now model number Agilent 8648A.
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I.
•
•
c,:
~
..,
..,
c
..,
..,
..,
ca.
.,;:
OPERATING
AND
SERVICE MANUAL
DISTORTION
ANALYZER
333A/334A
F/,o'I HEWLETT
a!/!111 PACKARD

•
•
•
________
F/,°oW
HEWLETT
______
_
~~
PACKARD
OPERATING
AND
SERVICE
MANUAL
MODEL
333A/334A
D
ISTO
RTIO
N
ANALYZER
Serial
Numbers:
333A:
1137A03146
and greater
334A:
1140A05641
and greater
Appendix
C, Manual
Backdating
Changes, adapts this
manual
to
lower
serial
numbers.
WARNING
I
To
help minimize the
possibility
of
electrical fire
or
shock
hazards, do
not
expose this
instrument
to
rain
or
excessive moisture.
Manual Part No. 00333-90008
Microfiche Part No. 00333-90058
©Copyright Hewlett-Packard Company
1966
P.O.
Box
301,
Loveland, Colorado,
80537
U.S.A
.
Printed: October 1975, 1985

•
•
•
Model 333A/334A
Table of Contents
TABLE OF CONTENTS
Section
I GENERAL INFORMATION •
1-1. Description •••..
1-6. Accessory Features.
1-8. Option •••••..•
1-10. Instrument Identification
Section
II INSTALLATION.
2-1. Introduction •
2-3. Inspection ••
2-5. Power Requirements
2-7. Three-Conductor Power Cable
2-10. Installation ••..•.
2-12. Bench Installation •.•
2-14. Rack Installation ••••
2-16. Repackaging For Shipment
Section
III OPERATING INSTRUCTIONS
3-1. Introduction • . • • . •
3-4. Controls and Indicators •
3-6. General Operating Information •
3-7. Input Connections •••.•
3-9. Voltmeter Characteristici:
3-12. Output Terminals ••
3-14. Operating Procedures ••
3-15. Instrument Turn-On •
3-16. Adjustment of Meter
3-18.
3-21.
3-22.
3-23.
3-27.
3-30.
Mechanical Zero. •
Distortion Measurement
Distortion Measurement of AM
RF Carriers (334A only).
Voltage
Measurement •••
Meter Indication • • • • •
Use of Output
Terminals .
333A/334A with Option 01
3-32. Manual Nulling •
Section
IV THEORY
OF OPERATION •
4-1. Overall Description.
4-3. Block Diagram Description .
4-4. Distortion Measuring
Operation •.••••.
4-8. Distortion Measurement in AM
4-10.
4-12.
4-13.
4-17.
4-39.
4-41.
4-49.
4-54.
Section
Carriers •••••..••
Voltmeter Operation .•••.
Detailed Circuit Description • • .
Impedance Converter Circuit .
Rejection Amplifier Circuit.
High Pass Filter . • • . • • •
Meter Amplifier ••.•••.
Power Supply Circuit • • • • .
RF Detector Circuit (334A only)
V MAINTENANCE • . • • • • . • •
5-1. Introduction •••••..•
5-3. Required Test Equipment •
Page
1-3
1-3
1-3
1-3
1-3
Page
2-1
2-1
2-1
2-1
2-1
2-1
2-1
2-1
2-1
Page
3-1
3-1
3-1
3-1
3-1
3-1
3-2
3-2
3-2
3-2
3-2
3-3
3-3
3-4
3-4
3-4
3-4
Page
4-1
4-1
4-1
4-1
4-1
4-1
4-1
4-1
4-2
4-5
4-5
4-7
4-7
Page
5-1
5-1
5-1
Section
V MAINTENANCE (Cont'd) •.••••.•.
5-5, Performance Checks •.....•
5-9. Fundamental Rejection Check
5-10. Second Harmonic Accuracy ..
5-11. Instrument Induced
5-12.
5-13.
5-14.
5-17.
5-18.
5-19.
5-20.
5-21.
5-22.
Distortion Check. . . . . . .
Frequency Calibration Accuracy
Check •..•..•......
Automatic Nulling Mode Check
Input Impedance Check . . .
Minimum Input Level Check. •
DC Isolation Check . . . . . .
Voltmeter Accuracy and
Frequency Response Check.
High Pass Filter Check • •
Residual Noise Check . • . . •
AM Detector Check (Model
334A only)
.••••..
5-23. Adjustment and Calibration
5-26.
5-27.
5-28.
Procedure .......••
Power Supply and Bias
Adjustments • • • . • • . • .
Voltmeter Gain Adjustments .
Voltmeter Frequency Response
Adjustment • • • • • • • • .
5-29. Bridge Balance Adjustment ••
5-30. Sensitivity SwitchCalibration.
5-31. Adjustment of Factory Selected
Components . • • • • • •
5-33. Troubleshooting Procedure .•
5-38. Troubleshooting Voltmeter
Function •.•...•..
5-40. Troubleshooting Distortion
Function .•.....•••
5-45. Photoresistor Check and
Adjustment (A6Vl thruA6V5).
5-49. Servicing Etched Circuit
Boards •••.....•
5-52. Servicing Rotary Switches.
5-54. Isolating the Impedance
Converter . . . ...
Section
VI REPLACEABLE PARTS ..
6-1. Introduction •.••.
6-4. Ordering Information •
6-6. Non-Listed Parts .•.
Section
VII CIRCUIT DIAGRAMS .
7
-1. Introduction • . •
Appendix
A CODE LIST
OF MANUFACTURERS
B
C
SALES AND SERVICE OFFICES
MANUAL BACKDATING CHANGES
Page
5-1
5-1
5-1
5-2
5-2
5-3
5-4
5-4
5-5
5-5
5-6
5-7
5-7
5-7
5-8
5-8
5-8
5-10
5-10
5-11
5-11
5-11
5-12
5-14
5-15
5-16
5-16
5-16
Page
6-1
6-1
6-1
6-1
Page
7-1
7-1
iii

-----
-
-------
- -
----------
Table
of
Contents
Model
333A/334A
LIST
OF
TABLES
Number
Page
Number
1-1.
Specifications.
. • . . . . . . .
1-1
5-5.
Power
Supply
and
Bias
Adjustments
.
3-1.
Effect
of
Harmonics
on Voltage
5-6.
Sensitivity
Switch
Calibration
Measurements.
. . . . . . .
3-1
5-7.
Factory
Selected
Components
5-1.
Required
Test
Equipment.
. . •
5-0
5-2. Second
Harmonic
Accuracy
Check
•
5-2
5-8.
Troubleshooting
Aid .
5-3.
Frequency
Calibration
Accuracy
Check
5-4
5-9.
Photoresistor
Check
•
5-4.
Voltmeter
Frequency
Response
Check
5-6
6-1.
Replaceable
Parts
..
Page
5-8
5-12
5-12
5-13
5-15
6-6
LIST
OF
ILLUSTRATIONS
Number
1-1. Model 333A
Distortion
Analyzer
3-1.
Front
and
Rear
Panel
Description
.
3-2.
Manual Nulling
Test
Setup
3-3.
Impedance
Correction
Graph
• . .
4-1.
Block
Diagram
. • . • • . • . .
4-2.
Bridge
Waveforms
. . .
•.•
4-3. Wien
Bridge
Circuit
and
Rejection
Characteristics
. . . • . • . .
4-4. Auto
Control
Loop
Detector.
.
•..
4-5.
Reference
and
Error
Phase
Relationship
• . • • • . .
•...
4-6.
Rejection
Amplifier
Block
Diagram
and
Typical
Frequency
Rejection
Characteristic
. . • • •
4-7.
Bandwidth
Versus
Null Depth
.•
4-8.
Simplified
Metering
Circuit
..•
5-1.
Fundamental
Rejection
Check
5-2.
Instrument
Induced
Distortion
Check
.•
5-3.
Frequency
Calibration
Accuracy
Check
iv
Page
1-1
3-0
3-5
3-5
4-0
4-2
4-3
4-3
4-4
4-5
4-6
4-7
5-1
5-2
5-3
Number
Page
5-4.
5-5.
5-6.
5-7.
5-8.
6-1.
6-2.
6-3.
7-1.
7-2.
7-3.
7-4.
7-5.
7-6.
Capacitance
Check
. • • • •
DC
Isolation
Check
. . . • .
Voltmeter
Accuracy
and
Frequency
Response
Check
. .
Shielded
Load
Assembly
.
Adjustment
and
Chassis
Mounted
5-5
5-6
5-7
5-8
Component
Location.
. .
5-9
Mechanical
Parts
. .
6-2
Modular
Cabinet
Parts
• .
6-4
Frequency
Tuning
Assembly
6-5
Internal
Wiring
Data.
. . .
7-3/7-4
Impedance
Converter
(P/0
A2)
and
RF
Detector
(A4) . . • . . . .
7-5/7-6
Rejection
Amplifier
(A3),
Bridge
Balance
(P/OA6)
and
High
Pass
Filter
(A7)
7-7/7-8
Meter
Amplifier
(P/0
A2)
......
7-9/7-10
Control
Circuit
(A5)
and
Bridge
Balance
(P/0
A6)
.
Power
Supply (Al) . . . . . •
7-11/7-12
7-13/7-14
t)

•
•
•
-------
F/ip'9
HEWLETT
~~
PACKARD
SAFETY
SUMM°ARY
The
following
general
safety
precautions
must
be
observed
during
all
phases
of
operation,
service,
and
repair
of
this
instrument.
Failure
to
comply
with
thasa
precautions
or
with
specific
warnings
alsawhara
in
this
manual
violates
safety
standards
of
design,
manufacture,
and
intended
use
of
the
instrument.
Hewlett-Packard
Company
assumes
no
liability
for
the
customer's
failure
to
comply
with
these
requirements.
This
is
a
Safety
Class
1
instrument.
GROUND
THE
INSTRUMENT
To
minimize shock hazard,
the
instrument
chassis and
cabinet
must
be
connected
to
an elec-
trical ground. The
instrument
is equipped
with
a
three-conductor
ac
power
cable. The
power
cable
must
either
be plugged
into
an approved
three-contact
electrical
outlet
or
used
with
a
three-contact
to
two-contact
adapter
with
the
grounding
wire
(green)
firmly
connected
to
an
electrical
ground
(safety
ground)
at
the
power
outlet.
The
power
jack
and
mating
plug
of
the
power
cable
meet
International
Electrotechnical
Commission
(IEC)
safety
standards.
DO
NOT
OPERATE
IN
AN
EXPLOSIVE
ATMOSPHERE
Do
not
operate
the
instrument
in
the
presence
of
flammable
gases
or
fumes.
Operation
of
any
electrical
instrument
in such an
environment
constitutes
a
definite
safety
hazard.
KEEP
AWAY
FROM
LIVE
CIRCUITS
Operating personnel
must
not
remove
instrument
covers.
Component
replacement
and
internal
adjustments
must
be made
by
qualified
maintenance
personnel. Do
not
replace
components
with
power
cable connected.
Under
certain
conditions,
dangerous
voltages
may
exist
even
with
the
power
cable removed.
To
avoid injuries,
always
disconnect
power
and
discharge
circuits
before
touching
them.
DO
NOT
SERVICE
OR
ADJUST
ALONE
Do
not
attempt
internal service
or
adjustment
unless
another
person, capable
of
rendering
first
aid and resuscitation, is present.
DO
NOT
SUBSTITUTE
PARTS
OR
MODIFY
INSTRUMENT
Because
of
the
danger
of
introducing
additional hazards,
do
not
install
substitute
parts
or
per-
form
any
unauthorized
modification
to
the
instrument.
Return
the
instrument
to
a
Hewlett-
Packard Sales and Service
Office
for
service and repair
to
ensure
that
safety
features
are
main-
tained.
DANGEROUS
PROCEDURE
WARNINGS
Warnings, such
as
the
example
below,
precede
potentially
dangerous
procedures
throughout
this
manual.
Instructions
containec;t
in
the
warnings
must
be
followed.
I-
WARNING
I
Dangerous
voltages,
capable
of
causing
death,
are
present
in
this
instrument
Use
ex-
trema
caution
when
handling,
tasting,
and
adjusting
.
A

SAFETY SYMBOLS
General Definitions of Safety Symbols Used On Equipment or In Manuals.
,,
Instruction manual symbol: the product will be marked with this
symbol when it
is necessary for the user to refer to the instruction
manual in order to protect against damage to the instrument.
Indicates dangerous voltage (terminals fed from the interior by
voltage exceeding
1000 volts must be so marked).
Protective conductor terminal. For protection against electrical
-1-
OR ~ shock in case of a fault. Used with field wiring terminals to in-
-
~ dicate the terminal which must be connected to ground before
177 OR .L
operating equipment.
Low-noise
or noiseless, clean ground (earth) terminal. Used for a
signal common, as well
as providing protection against electrical
shock in case
of a fault. A terminal marked with this symbol must
be connected
to ground in the manner described in the installation
(operating) manual, and before operating the equipment.
Frame
or chassis terminal. A connection to the frame (chassis) of
the equipment which normally includes all exposed metal struc-
tures.
Alternating current (power line).
Direct current (power line).
Alternating
or direct current (power line).
WARNING
IThe WARNING sign denotes a hazard. It calls attention
to a pro-
cedure, practice, condition
or the like, which, if not correctly per-
•-----•- formed or adhered to, could result in injury or death to personnel.
NOTE:
The CAUTION sign denotes a hazard. It calls attention to an
operating procedure, practice, condition or the like, which,if not
correctly performed
or adhered to, could result in damage to or
destruction of part or all of the product.
The NOTE sign denotes important information. It calls attention
to procedure, practice, condition
or the like, which is essential to
highlight.
0
tJ

•
•
•
Model
333A/334A
Section
I
SECTION
I
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
pf
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
O.
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
at
the
OUTPUT
connectors
with
an
oscilloscope,
a
true
rms
voltmeter,
or
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 5 Hz
to
3 MHz (20 Hz
to
500 kHz
for
300
µ
V
range)
and
a
voltage
range
of 300
µ
V
to
300 V
rms
full
scale.
1-5.
The
AM
detector
included
in
the
Model
334A
is
a
broadband
de
restoring
peak
detector
consisting
of
a
semiconductor
diode
and
filter
circuit.
AM
distor-
tion
ievels
as
low
as
0.
3%
can
be
measured
on
a 3 V
to
8 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
O.
1%-100%
are
measured
full
scale
in
7
ranges.
DISTORTION MEASUREMENT ACCURACY
Harmonic
measurement
accuracy
(full
scale)
Fundamental
Input
Less
Than
30 V
RANGE
±3%
±6%
±12%
100%-0.
3%
10 Hz
10
Hz
1 MHz 3 MHz
0.1%
30
Hz
20 Hz
10
Hz
300 kHz 500 kHz
1.2
MHz
1-6.
ACCESSORY FEATURES.
1-7.
The
accessory
available
with
the333Aand334A
Distortion
Analyzers
is
a
voltage
divider
probe,
-hp-
Model
No. 10001A.
The
features
of
the
probe
are:
a.
10
megohms
shunted
by 10
pF,
giving
10:1
attenuation.
b.
DC
to
30 MHz bandwidth.
c.
2%
division
accuracy.
d. 600 V
peak
input.
e.
5
ns
rise-time.
1-8.
OPTION.
1-9.
Option
01
is
a
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.
If a
letter
is
included
with
the
serial
number,
it
identifies
the
coun-
try
in
which
the
instrument
was
manufactured.
If
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
Appen-
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
RANGE
±3% ±6%
±12%
100%-0.
3%
10
Hz
10Hz
10 Hz
300 kHz 500 kHz 3 MHz
0.1%
30
Hz
20
Hz
10
Hz
300 kHz 500 kHz
1.2
MHz
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 dB 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± 10% from 300 kHz to 600 kHz
INPUT IMPEDANCE
Distortion Mode: 1 Mn ±5% shunted by <70 pF.
Voltmeter Mode:
1
Mn ±5% shunted by <30 pF (333A only),
1
Mn ±5% shunted by <35 pF (334A only),
1
to 300 V ranges; 1 Mn ±5% shunted by<70pF,
300 µ V to O. 3 V ranges.
INPUT LEVEL FOR DISTORTIONMEASUREMENTS
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 Xl frequency range is 50dB
below the fundamental.
DC ISOLATION
Signal
ground may be ±400 Vdc from external
chassis.
VOLTMETER RANGE
300 µ V
to 300 V rms full scale (13 ranges),
10 dB per range.
VOLTMETER FREQUENCY RANGE
5 Hz
to 3 MHz (300 µ V range: 20 Hz-500 kHz).
VOLTMETER ACCURACY:
RANGE
±2% ±5%
300 µV 30 Hz-300 kHz 20 Hz-500kHz
1 mV-30 V 10 Hz-1 MHz 5 Hz-3 MHz
100V-300V 10 Hz-300 kHz 5 Hz-500 kHz
NOISE MEASUREMENTS
Voltmeter residual noise on the 300 µ V range:
< 25 µ V rms terminated in shielded 600n; <30
µ V
rms terminated in shielded 100 kn.
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
kn for full scale meter deflection.
AUTOMATIC NULLING MODE
Set Level: At least O. 2 V rms.
Frequency Ranges:
Xl, manual null tuned to less than 3% of set
level; total frequency hold-in ±0. 5% about
true manual null.
XlO through XlO K, manual null tuned to
less than 10% of set level; total frequency
hold-in± 1% about true manual-null.
AUTOMATIC NULL ACCURACY
5 Hz
to 100 Hz: Meter reading within Oto +3
dB of manual null.
100 Hz
to 600 kHz: Meter reading within O to
+1. 5 dB of manual null.
HIGH-PASS
FILTER
3 dB point at 400 Hz with 18 dB per octave roll
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.
r------------------------------------------
MODEL 334A
Same
as Model 333A except as indicated below:
AM DETECTOR
High
impedance de 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
1-2
550kHz to 1. 6 MHz: Distortion introduced by
detector is < O. 3% for 3 to 8 volt carriers
modulated 30%.
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 1 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.
0i

.
•
•
•
Model 333A/334A Section II
SECTION
II
INSTALLATION
2-1.
INTRODUCTION.
2-2.
This
section
contains
information
and
instruc-
tions
necessary
for
the
installation
and
shipping
of the
Models
333A/334A
Distortion
Analyzers.
Included
are
~itial
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
should
be
physically
free
of
mars
or
scratches
and in
perfect
electrical
order
upon
receipt.
To
confirm
this,
the
instrument
should be
inspected
for
physical
damage
in
transit.
Also
check
for
supplied
accessories
and
test
the
electrical
performance
of the
instrument'
using
the
procedure
outlined in
Paragraph
5-5.
If
!he7e
is
damage
or
deficiency,
see
the
warranty
on
the
ms1de
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.
To
protect
operating
personnel,
the
National
Electrical
Manufacturers'
Association
(NEMA)
recom-
mends
that
the
instrument
panel
and
cabinet
be
grounded.
All
Hewlett-Packard
instruments
are
equipped
with
a
three-conductor
power
cable,
which, when plugged
in-
to
an
appropriate
receptacle,
grounds
the
instrument.
The~ffsetpinon
the
power
cable
three-prong
connec-
tor
1s
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°
F).
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"
Rack
Mount 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 a
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.)
If
the
instrument
is
to
be
shipped·
to
Hewlett-Packard
for
service
or
repair,
attach
a
tag
to
the
instrument
identify-
ing the
owner
and
indicate
the
service
or
repair
to
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:
a.
Place
instrument
in
original
container
if
avail-
able.
If
original
container
is
not
available,
a.suitable
one
can
be
purchased
from
your
nearest
-hp-
Sales
and
Service
Office. .
b.
Ensure
that
container
is
well
sealed
with
strong
tape
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
panel
face
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

i
I.
Section
m
Model 333A/334A
@ @
® ®
@ @
G)
LINE switch
turns
instrument
ac
power on.
Pilot
lamp glows when
instrument
is
turned
ON.
@Meter
indicates
distortion
or
voltage
level
of
input.
Q)MODE
switch
selects
MANUAL
or
AUTOMATIC
bridge
tuning operation
..
©FREQUENCY
RANGE
switch
selects
frequency
range
which
corresponds
to fundamental of input
signal.
G)coARSE
BALANCE
control
provides
coarse
ad-
justment
for
balancing the Wien
bridge
circuit.
(!)FINE
BALANCE
control
provides
a
vernier
ad-
justment
for
balancing the Wien bridge
circuit.
(!)Frequency
dial
tunes the Wien bridge
circuit
to
fundamental of input signal.
C!)HlGH 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.
@Frequency
vernier
provides
fine
adjustment
of
frequency
dial,
@
METER
RANGE
switch
selects
full
scale
range
of
meter
in
percent,
dB and
rms
volts.
CAUTION!
-R.F
0£TECTOR-
M"K
INPUT
VOLTAGE
40
VOLT
P-PAC
OR
40
VOLT PEAK TRANSIENT
@sENSITIVITY
selector
provides
I) -
50 dB attenu-
ation of input
signal
in
10 dB
steps
in
SET LEVEL
and DISTORTION functions.
@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.
@shorting
bar
connects
circuit
ground to
chassis
ground.
@INPUT
terminals
provide
connections
for
input
signal.
@NORM
RF
DET (Model 334A only)
selects
front
panel
INPUT
or
rear
panel
RF
INPUT connector.
@RF
INPUT connector (Model 334A only)
provides
input connection
for
AM
RF
carrier
input signal.
@
FUSE
provides
current
overload
protection
for
instrument
circuits.
@
Line voltage switch
sets
instrument
to
operate
from
100
V
/120
V
/220
V
/240
V.
@
Ac power connector
provides
input connection
for
ac
power.
Figure
3-1.
Front
and
Rear
Panel
Description
3-0

•
•
•
Model 333A/334A Section
m
SECTION
Ill
OPERATING INSTRUCTIONS
3-1.
INTRODUCTION.
3-2.
The Models 333A and 334A
DistortionAnalyzers
measure
total
harmonic
distortion
of
fundamentalfre-
quencies
from
5
Hz
to
600
kHz;
harmonics
upto3MHz
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.
An
rms
calibrated
voltmeter
is
inherent
in
the
333A and 334A. The
voltmeter
provides
a full
scale
sensitivity
of 300 µ
volts
rms
(residual
noise<25µ 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.
3-5.
Figure
3-1
illustratesanddescribesthefunction
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
based
on
the
ratio
between
the
average
andeffective
(rms)
values
of a
pure
sine
wave. The
ratio
of
average
to effective
values
in a
true
sine
wave
is
approximately
O.
9
to
1.
When
the
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
in a .sine wave.
The
amount of deviation depends on
the magnitude and phase
relation
between
the
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.
As
in-
dicated
in
the
table,
harmonic
content of
less
than
10%
results
in
very
small
errors.
Table
3-1
Effect
of
Harmonics
on Voltage
Measurements
Input Voltage
True
Meter
Characteristics
RMS
Value Indication
Fundamental = 100 100 100
Fundamental +
10%
100. 5
100
2nd
harmonic
Fundamental +
20%
102
100 -102
2nd
harmonic
Fundamental +
50%
112
100
-110
2nd
harmonic
Fundamental +
10%
100. 5 96 -104
3rd
harmonic
Fundamental +
20%
102
94 -108
3rd
harmonic
Fundamental +
50%
112
90 -116
3rd
harmonic
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
tne fundamental frequency
is
suppressed
and the
re
-
mainder
of the
signal
is
measured,
the
reading
ob-
tained
on
an
average
responding
meter
may deviate
from
the
true
total
rms
value. When the
residual
wave contains many inharmonically
related
sinusoids,
tne maximum
error
in the
distortion
reading
is
about
11
% (11 %of the
measured
distortion)
low
for
dis-
tortion
levels
below
10
%.
EXAMPLE:
Measured
Distortion
2.5%
Maximum
Error
In
Meter
Indication
+O.
llxO.
025=
0.00027
Total
Distortion
0.025+0.0027=
0. 0277
or
2.
8%
This
example
represents
the
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

rr,--~---. ~--~- -c-.-~-------·--~----
:
I
i
I
I Section III
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. Set the 115-230 VAC switch to coincide with the
line voltage in use. Turn switch to ON position.
Pilot lamp will glow, 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-
til pointer is left 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. Il
pointer moves off zero, repeat steps c through
e, but make counterclockwise rotation less.
3-18. DISTORTION MEASUREMENT.
DO NOT EXCEED THE INPUT VOLT-
AGES LISTED BELOW TO PREVENT
DAMAGING COMPONENTS
ON A2
BOARD.
VOLTMETER FUNCTION
-lV
RANGE AND BE LOW, AND
DISTORTION ANALYZER
FUNCTION -
MAXIMUM
SENSITIVITY.
1. 300 V ABOVE 100 Hz
2.
50 V ABOVE 1 kHz
3-19. MANUAL MODE.
3-2
a. Turn instrument on and mechanically zero
meter according to procedure in Paragraphs
3-15 and 3-16.
Model 333A/334A
b. Set NORM-R. F. DET. switch to NORM.
c. Set FUNCTION
switch to SET LEVEL.
d. Set MODE
switch to MANUAL.
e. H
fundamental frequency is 1kHz or greater,
set HIGH PASS FILTER switch to IN.
f. Set SENSITIVITY selector to MIN. position,
and rotate VERNIER control maximum
counterclockwise.
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}.
g. Set METER RANGE switch to SET LEVEL,
and set BALANCE COARSE and FINE con-
trols to center position.
h. Connect signal to be measured to 333A/334A
INPUT
terminals.
I WARNING I
REMOVE SHORTINGSTRAPBETWEEN
FRAME GROUND ( .L.} AND CHASSIS
GROUND (
,& }TERMINALS ON FRONT
PANEL INPUT TERMINALS WHEN
MEASURING DISTORTION BETWEEN
TWO POINTSWHICH ARE
DC OFFSET
FROM GROUND POTENTIAL.
i. Set SENSITIVITY
selector to obtain meter
indication greater than 1/3 full scale.
j. Adjust SENSITIVITY VERNIERfor full scale
meter indication if making distortion measure-
ment in percent; if making distortion measure-
ment in dB adjust SENSITIVITY VERNIER
for O dB meter indication.
~~~~~NOTE~~~~-
Il unable to adjust for full scale
or OdB indication, (which indicates
input signal is below O. 3 volts},
set METER RANGE selector down-
scale. Use this new setting as the
100%or OdB SET LEVEL position,
thus making the next range 30%
or -10 dB, etc.
k. Set FREQUENCYRANGE switch and frequency
dial to fundamental frequency of input signal.
1. Set FUNCTION switch to DISTORTION.
m.
Adjust frequency dial vernier and BALANCE
COARSE
and FINE controls for minimum

•
•
•
Model 333A/334A
n.
meter
indication. Set
METER
RANGE
switch
down-scale
as
necessary
to
keep
meter
in-
dication
on
scale.
Repeat
step
m until no
further
reduction
in
meter
indication
can
be
obtained.
o.
Observe
distortion
either
in
percentage
or
dB,
as
indicated
by
meter
deflection
and
METER
RANGE
switch
setting.
For
example,
if
meter
indicates
O.
4
and
METER
RANGE
setting
is
1%,
distortion
measured
is
0.4%
of
fundamental.
Similarly,
if
meter
indi-
cates
-6
dB
and
METER
RANGE
setting
is
-40
dB,
distortion
measured
is
-46
dB
from
fundamental.
~~~~-NOTE~~~~~-
In
MANUAL mode
the
accuracy
of
distortion
measurements
is
affected
by
frequency
stability
of
the
input
signal.
An
inaccuracy
in
distortion
indications
occurs
when
the
frequency
drift
of
the
input
signal
exceeds
the
bandwidth
of
the
rejection
curve.
p.
If
desired,
rms
voltage of input
signal
can
be
measured
by
setting
FUNCTION
switch
to
VOLTMETER, and
setting
METER
RANGE
switch
to
obtain
an
on-scale
indication.
3-20. AUTOMATIC MODE.
a.
Perform
steps
athroughlof
Paragraph
3-19.
b.
Adjust
frequency
dial
vernier
and
BALANCE
COARSE
and
FINE
controls
for
minimum
meter
indication.
c. When
meter
indication
is
less
than
10%
of
SET
LEVEL
indication,
set
MODE
switch
to
AUTOMATIC.
(If
fundamental
cannot
be
manually
nulled
below
10%
of SET
LEVEL
indication,
automatic
mode
cannot
be
used).
d. Set
METER
RANGE
switch
down-scale
to
obtain
on-scale
meter
indication.
e.
Observe
distortion
either
in
percentage
or
dB,
as
indicated
by
meter
deflection
and
METER
RANGE
switch
setting.
For
example,
if
meter
indicates
0.
4
and
METER
RANGE
setting
is
1%,
distortion
measured
is
0.
4%
of
fundamental.
Similarly,
if
meter
indicates
-6
dB
and
METER
RANGE
setting
is
-40
dB,
distortion
measured
is
-46
dB
from
funda-
mental
.
f.
If
desired,
rms
voltage of input
signal
can
be
measured
by
setting
FUNCTION
switch
to
VOLTMETER, and
setting
METER
RANGE
switch
to
obtain
an
on-scale
indication.
Section m
3-21.
DISTORTION MEASUREMENT
OF
AM
RF
CARRlERS (334A only).
DO
NOT EXCEED MAXIMUM INPUT
VOLTAGESLISTEDONREARPANEL.
a.
Turn
instrument
on
and
mechanically
zero
meter
according
to
procedure
in
Paragraphs
3-15
and
3-16.
b. Set NORM.-R.
F.
DET.switch
to
R.
F.
DET.
c.
Connect input
signal
to
R.
F.
INPUT
terminal
on
rear
panel.
d.
Refer
to
Paragraph
3-19
for
manual
distort-
ion
measurement;
refer
to
Paragraph
3-20
for
automatic
distortion
measurement.
If
no
meter
deflection
can
be
obtained
with
an
RF
input, diode
A4CR1
should
be
checked.
A
spare
diode
is
located
on
the
outside
of
the
A4
shield.
3-22.
VOLTAGE MEASUREMENT.
a.
Turn
instrument
on
and
mechanically
zero
meter
according
to
procedure
in
Paragraphs
3-15
and
3-16.
b. Set NORM.- R.
F.
DET.
switch
to
NORM.
c.
Set FUNCTION
switch
to
VOLTMETER.
d.
Set
METER
RANGE
switch
to
a
range
exceeding
amplitude
of
signal
to
be
mea-
sured.
e.
Connect
signal
to
be
measured
to
INPUT
terminals.
f. Set
METER
RANGE
switch
to
give a
reading
as
close
to
full
scale
as
possible,
and
ob-
serve
meter
indication.
g.
The
dB
scale
of
the
333A/334A
is
calibrated
in
dBm,
such
that
O
dBm
=
1
milliwatt
dissi-
pated
by
600
ohms.
Therefore,
a dBm
mea-
surement
must
be
made
across
600
ohms.
However, dB
measurements
across
other
impedances
can
be
converted
to
dBm
by
use
of
the
Impedance
Correction
Graph
of
Fig-
ure
3-3.
For
example:
to
convert
a -30 dB
reading
across
200
ohms
to
dBm,
locate
the
200 ohm
impedance
line
at
the
bottom of
the
graph.
Follow
the
impedance
line to
the
heavy
black
line,
and
read
the
meter
correc-
tion
at
that
point.
The
correction
for
200
ohms
is
+5
dBm;
thus
the
corrected
reading
is
-25
dBm.
3-3

Section m
3-23. METER INDICATION.
3-24. The 333A/334A meter is calibrated to indicate
in both dB and volts. It is interesting to note that 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 in the 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 on the 333A/334A
corresponds to 0. 3 volt range rather than the 1 volt
range. This allows a 10 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 O dB becomes the -10 dBm range for absolute
power measurements. Zero dBm is equal to 1 milli-
watt dissipated by any impedance and in this 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, utilize the 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. lnVOLTMETERand SET LEVEL functions, the
333A/334A can be used as a low distortion, wide-band
amplifier. A portion of the meter input (0. 1 V rms
open circuit for full scale meter deflection is provided
at the OUTPUT terminals.
3-29. In DISTORTION function, the distortion (0. 1 V
rms open circuit for full scale deflection) is provided
at the OUTPUT terminals for monitoring purposes.
3-4
~~~~~-NOTE~~~~~
The INPUT ,& terminal and the
OUTPUT ,& terminal should not 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/334A
3-30. 333A/334A WITH OPTION 01.
3-31. Operating procedures for the 333A/334A with
OptionO1
are the same as for the standard instrument.
The only difference between the standard and optional
instrument is that the Option 01 has a special meter
and meter amplifier which is 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 supplied to simplify nulling the
333A/334A in the MANUAL mode. When nulling the
333A/334A 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.
a. ""1i.¥Ylti'klli No harmonic distortion. Frequency
and balance adjustment correct.
Frequency and balance control im-
properly adjusted.
Frequency approximately correct;
balance incorrect.
d. C:::::, Balance approximately correct; fre-
quency incorrect.
e. 00 Second harmonic predominant; fre-
quency and balance adjusted.
f. .....----- Second harmonic predominant; fre-
quency and balance adjusted; phase
changed.
g. _____..... Second harmonic predominant; fre-
quency and balance adjusted; phase
changed.
h. cx::x::> Third harmonic predominant.
i.~
j.o
Balance incorrect; meter reading of
scale.
Frequency incorrect; meter readinf
off scale.
tJJ)
@))

I.
""'
I
0
! INPUT
I
JI)-
~
57
I
FUNCTION
I
0
I
P/0
SI
I
I
VOLTMETER
I
I
METER
RANGE
I
Qs3
!---------------
----------------------
- -
------
--
- -
--------,
I
I
P/0
SI
P/0
SI
P/0
SI
@@
I
SET
LEVEL
I
1:1
AND
1000:1
ATTENUATOR
S3R12-S3Rl3
I
I
IMPEDANCE
CONVERTER
A2QI-A2Q4
rRFINPUT.,
L----J
JS
'>-----I
AM
DET
(334A
ONLY)
90°
PHASE
LAG
(REF)
PHASE
DET
I'>.
I
SENSITIVITY
~
VERNIER
S2R8
!AUTO
I
!MANUAL!
I
FIXED
VOLTAGE
58
I
DISTORTION
I I
SENSITIVITY
I
Qs2
IMEG
OHM
ATTENUATOR
S2RI-
S2R6
I
I
I
I
I
I
I
I
I
I
I
I
I I
~-----------------------~--------------~---
-•--
-
_J
J
REJECTION AMPLIFIER
(-)FEEDBACK
PREAMPLIFIER
!------'-------+--------,
I
I
._
____
__.
PO/SI I
LAMP
DRIVER
~
/,'/
'/y
BRIDGE
AMPLIFIER
- -
-0
I
BALANCE
I
LAMP
DRIVER
58
! AUTO!
---------------~
I
MANUAL!
I
FIXED
VOLTAGE
POST
ATTENUATOR
S3RI-S3RII
METER CIRCUIT
A2Q5-A2Q9
A2CR6-A2CR7
Ml
PHASE
DET
(REF)
333A/3l4A·C•03Z8
'----------------------------------
.....
f---------------------------------------------'
-~-
i...,'=-'
\~
Figure
4-1.
Block
Diagram
'~
1£-:'lllj
-.e,,
IL=:.~
J2
Cl.l
Cl)
(")
....
....
0
;:,
....
<
~
0
0.
Cl)
-
w
w
w
>
'-.
w
w
t
__J

•
•
•
Model 333A/334A
Section IV
SECTION IV
THEORY OF OPERATION
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,
Ml. 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 signal is
applied to the impedance converter (Assembly A2)
through the FUNCTION selector, Sl, 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, S2. The
impedance converter provides impedance matching and
unity gain between the INPUT terminals and the input
of
the rejection amplifier.
4-6. The rejection amplifier consists of a preamplifier,
a Wien bridge, and a bridge 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 in the 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
level applied to the metering circuit to 1 mV for full
scale deflection. Sensitivity of the metering circuit
is increased to 300 µ V for full scale deflection on the
. 0003 Vrange. 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.
4-9. The Model 334A Distortion Analyzer contains an
AM detector circuit for 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. In the 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 on the 0. 0003 too. 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 µ 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
S3Rl2 in voltmeter operation, and through the one
megohm attenuator S2Rl through S2R6 in distortion
operation. Capacitive dividers S2Cl through S2C10
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 A2Ql to
the gate of A2Ql 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 a 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 A2Ql results in unity gain from the
impedance converter.
4-16. The bias points of the transistors in the imped-
ance converter are selected to minimize instrument
induced distortion. A2Ql, 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 {A3Ql thru A3Q3), the Wien bridge
resistive leg and auto control loop {A5Ql thru A5Q9
with
associated lamp and photocell), the reactive leg
and auto control loop {A5Ql0 thru A5Ql8 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 A3Rl0 and
A3Rl 1 is applied to the junction of A3R2 and A3C2 to
establish the operating point for A3Ql. Negative
feedback from the emitter of A3Q3 is applied to the
emitter of A3Ql 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. In the distortion measuring operation the Wien
bridge circuit is used as a rejection filter for the
fundamental frequency of the input signal. With the
FUNCTION selector, Sl, in the 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, and tuning the capacitors C4A
through C4D. The bridge circuit is balanced by ad-
justing the COARSE balance control, R4, and the 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 to be nulled, a portion of the fundamental
4-2
Model 333A/334A
I
I
I
I
I
I
I 1-
1 I' I \ I
I/ I \ I
OUTPUT OF BRIDGE ..-t, \I
IF RESISTIVE LEG B-+--;_._"......1.-'&--
IS UNBALANCED
OUTPUT
OF BRIDGE
IF REACTIVE LEG C-....._...;a:_.,.......,a:~ .... -
IS DETUNED
333A-B-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.
4-24. Figure 4-2a shows a sinusoid inputtothe 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 moo out of phase, if the null
position is passed. When the 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 900 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 180° 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.
t))]

:e
~·
•
Model 333A/334A
RI
E
IN
TYPICAL WIEN
BRIDGE
Section
IV
~RESULT
OF
FEEDBACK
~
I, '
-'1-+-f--++tHtl-t--+--\c~t+++ltJl"-,--f'++-
,H+HH--+-+--l+!-++H--1--+-++++Hi•
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-oo,
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-,.l+--1'+-l-l-ll!l
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..,.,'"=.,.--t-HH+I-Hi
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l--+-H-++H~h--+-+-~-l-H-lll-1--1
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•
,0
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.,~
..'..
0 •
..
,
-
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5 -
,0
!
:
-2~,,__..,__,'-'-+....,._.___,__.--+-+-<'"""'
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.w..w.u--'--~-'
Htftl·---t-HHH-lll·••
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IOO
FR(OIJ[HCT
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
(S4Rl,
3,
5, 7,
or
9
and
C4A/B)
and
the
shunt
reactive
leg
(S4Rll,
13, 15, 17,
or
19,
and
C4C/D),
is
the
same
as
at
the
midpoint
of
the
resistive
leg
(A3Rl2
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-
age
between
the
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
S4.
S4
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
A5Q7.
The
reference
voltage
is
amplified
and
clipped
by A5Q8
and
A5Q9,
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
A5Ql.
It
is
amplified
by A5Q2
and
A5Q3
and
coupled
to
the
detector
A5Q4.
4-30.
Refer
to
Figure
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
A5TP3
is
be-
tween
O
and-1
volt.
The
de output
of
the
filter
network
causes
the
voltage
at
A5TP3
to
go in a
positive
direc-
tion
(toward
zero)
for
in
phase
error
signals,
and in
a
negative
direction
(toward
-1
V)
for
outof
phase
error
signals.
The
change
in
base
voltage
is
then
amplified
by A5Q5
and
lamp
driver
A5Q6.
This
will
change
the
brilliance
of
lamp
A6DS1, which
will
vary
the
resist-
ance
of
A6Vl
in
the
direction
necessary
to
balance
the
resistive
leg
of
the
bridge.
COLLECTOR~
OFQ3
l
TP2
C6
RII
f\
f\
COLLECTOR
l
\JV
OF02
C5
TP3
RIO
TO
BASE
Of
05
r
Rl3
CB
Figure
4-4.
Auto
Control
Loop
Detector
4-3

i
.1
Section IV
4-33.
Refer
to
Figure
4-5
for
the
phase
relationship
of
the
bridge
error
signal
and
reference
voltage
at
the
base
of A5Q4.
The
shaded
portions
of
the
error
sig-
nals
(band
c)
indicate
that
part
of
the
error
signal
which
contributes
to
the
de
lamp
control
voltage.
As
indicated
ind,
any
error
signal
that
is
90°
outof
phase
with
the
reference
does
not
affect
the
de
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.
signal
for
Resistive
Detector
(A5Q4)
b
Resistive
Error
signal
in
phase
with
reference
at
bridge
C
ResJstive
Error
signal
180
out
of
phase
d
Re
8
ctive
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
e
I I
I I
I I
I I
I
I
I
I
Model 333A/334A
phase
delay
circuit,
A5Q15, A5Q16, S4AF
and
\
S4C1
through
S4C5,
shifts
the
reference
voltage
1
)))
90°,
as
shown
in
Figure
4-5f.
This
makes
the
detector
A5Q12
sensitive
to
components
of
the
bridge
error
signal
that
are
900 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
A5R56
in
parallel
with A5R55
on
the
top
three
fre-
quency
ranges.
A6DS2
will
become
brighter,
and
lower
the
resistance
of
A6V2
through
A6V5,
making
variation
f
Ref.
signal
for
Reactive
Detector
(A5Q
121
g
Reactive
Error
signal
in
phase
with
reference
at
bridge
h
Reactive
Error
signal
out of
phase
Re~istive
Error
signal
90
out
of
phase
(Results
in
no output
from
Re-
active
Detector)
Error
signal,·
Reactive
leg
detuned,
Resistive
leg
unbalanced
I I
I I
I I
I I
I
I
I
I
1))
Figure
4-5.
Reference
and
Error
Phase
Relationship
4-4