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TM 11-6625-1576-15
DEPARTMENT OF THE ARMY TECHNICAL MANUAL

ORGANIZATIONAL, DS, GS, AND DEPOT MAINTENANCE MANUAL

DISTORTION ANALYZER
HEWLETT-PACKARD MODELS 333A AND 334A

HEADQUARTERS, DEPARTMENT OF THE ARMY MAY 1967

TM 11-6625-1576-15

WARNING DANGEROUS VOLTAGES EXIST IN THIS EQUIPMENT Be careful when working on the power supply and on the 115-volt ac line connections. DO NOT TAKE CHANCES !

This manual contains copyrighted material originally prcpared by the Hewlett-Packard Co.

TM11-6625-1576-15
TECHNICAL MANUAL ) ) NO. 11-6625-1576-5 ) HEADQUARTERS DEPARTMENT OF THE ARMY Washington, D.C., 1 9 M a y 1 9 6 7

Organizational, DS, GS, and Depot Maintenance DISTORTION ANALYZER, HEWLETT-PACKARD MODELS 333A AND 334A Section I Page

GENERAL INFORMATION . . . . . . . . . 1-2.1 1-A.1 Scope . . . . . . . . . . . . . . . . .1-2.1 l-A.2 Index of Publications. . . 1 - 2 . 1 l-A.3 Forms and Records . . . . . . . . . . . 1 - 2 . 1 l-1. Description . . . . . . . .1-3 1-6. Accessory Features . . . . . . . .1-3 1-8. Options Available . . . . . . . . .1-3 1-11. Modifications . . . . . . . . . . . . . . . . . . . . . . . . 1-3

Page Section INSTALLATION . . . . . . . . . . . . . .2-1 II 2-1. Introduction . . . . . . . . . . . . . .2-1 2-3. Inspection . . . . . . . . . . . . . . 2-1 2-5. Power Requirements . . . . . . . . . . 2-1 2-7. Three-Conductor Power Cable . . . 2-1 2-10. Installation . . . . . . . . . . . . . . 2-1 2-12. Bench Installation . . . . . . . . . 2-1 2-14. Rack Installation . . . . . . . . . . 2-1 2-16. Repackaging for Shipment . . . . . . 2-1 Page Section OPERATING INSTRUCTIONS . . . . . . . 3-1 III 3-1. Introduction . . . . . . . . . . . . . 3-1 3-4. Controls and Indicators . . . . . . . 3-1 3-6. Adjustment of Mechanical Zero . . . 3-1 3-8. General Operating Information . . . 3-1 Input Connections . . . . . . . . . 3-1 3-9. 3-11. Voltmeter Characteristics . . . . . 3-1 3-14. Use of Output Terminals . . . . . . 3-1 3-16. Operating Procedures . . . . . . . . 3-2 3-18. Distortion Measurement . . . . . . 3-2 Page Section IV THEORY OF OPERATION . . . . . . . . . . 4-1 4-1. Overall Description . . . . . . . . 4-1 4-3. Block Diagram Description . . . . . 4-1 4-4. Distortion Measuring Operation . . 4-1 4-6. Distortion Measurement in AM . Carriers . . . . . . . . . . . . . 4-1 4-8. Voltmeter Operation . . . . . . . . 4-1 4-10. Schematic Theory . . . . . . . . . . 4-1 4-11. Impedance Converter Circuit . . . 4-1 4-14. Rejection Amplifier Circuit . . . . 4-2 4-36. High Pass Filter . . . . . . . . . . . 4-5 4-38. Meter Circuit . . . . . . . . . . . . 4-5 4-46. Power Supply Circuit . . . . . . . . . . 4-7 4-51. RF Detector Circuit (334A only) . l 4-7 Section Page V MAINTENANCE. . . . . . . . . . . . . 5-1 5-l. Introduction. . . . . . . . . . . 5-1 5-2. Test Equipment Required . . . . . 5-1 5-5. Performance Checks. . . . . . . . . 5-1

Section V (Cont `d) 5-9. Fundamental Rejection Check . . 5-10. Second Harmonic Accuracy Check 5-11. Distortion Introduced by Instrument Check and Automatic Control Loop Operation . . . . 5-12. Frequency Calibration Accuracy Check . . . . . . . . . . . . 5-13. Input Resistance Check . . . . . . 5-14. Input Shunt Capacitance Check . . 5-15. Minimum Input Level Check . . . 5-16. DC Isolation Check . . . . . . . . 5-17. Voltmeter Accuracy Check . . . . 5-18. High Pass Filter Check . . . . . . 5-19. Voltmeter Frequency Response Check . . . . . . . . . . . . . . . . 5-20. Residual Noise Check . . . . . . . 5-21. AM Detector Check (Model 334A only) . . . . . . . . . . . . . . . 5-22. Adjustment and Calibration Procedure. . . . . . . . . . . . . . . 5-25. Meter Mechanical Zero Set . . . . 5-27. Power Supply and Bias Adjustments. . . . . . . . . . . 5-28. A3R16 and A3R30 Distortion Adjust. . . . . . . . . . . . . . 5-29. Bridge Balance Adjustment (C3) . 5-30. Voltmeter Gain Adjustments . . . 5-31. Voltmeter Frequency Response Adjustment . . . . . . . . . . . 5-32. Sensitivity Switch Calibration . . . 5-33. Troubleshooting Procedures . . . . 5-39. Bottom Shield Removal . . . . . . 5-41. Servicing Etched Circuit Boards . 5-44. Servicing Rotary Switches . . . . Section VI SCHEMATIC DIAGRAMS 6-1. Schematic Diagrams

Page 5-1 5-2 5-2 5-3 5-4 5-4 5-4 5-4 5-5 5-5 5-6 5-6 5-6 5-7 5-7 5-7 5-9 5-9 5-10 5-10 5-10 5-11 5-11 5-11 5-13 Page 6-1 6-1

i i i

TM 11-6625-1576-15
Model 333A/334A Section 1 Figure 1-1 and Table 1-1

Figure 1-1. Model 333A Distortion Analyzer Table 1-1. Specifications

1-1

TM 11-6625-1576-15
Section I Table 1-1 Table 1-1. Specifications (Cont `d) Model 333A/334A

1-2

TM 11-6625-1576-15
SECTION I GENERAL INFORMATION 1-A.1 Scope manual includes installation and operation instructions general and support

This covers

operator's,

organizational,

direct

support

(DS),

(GS), and depot maintenance. It describes Hewlett-Packard (Federal support Code 80537) Distortion Analyzer Models 333A and 334A (fig. l-l). A basic issue items list for this equipmnent is not included as part of this manual.

1-A.2

Index

of

Publications

Refer to the latest issue of DA Pam 310-4 to determine whether there are new editions, DA changes, 310-4 and the or is additional an index of work to publications current orders the and pertaining to the equipment. lubrication publications -20, 35P, publication. l-A.3 a. ment b. DD AR air c. Forms and of and of Records and Unsatisfactory Equipment. with instructions Fill out in Use TM equip38-750. Pam technical that are of manuals, available parts each through

technical bulletins, supply manuals (types 7, 8, and 9), supply bulletins, orders, supply etc) and modification The latest channels. index lists individual (-10,

changes

revisions

equipment

Reports forms Report Form 700-58 6

Maintenance records Damaged of in or

accordance Improper or

Shipment. 378

and as

forward in `71-4

(Report (Army),

Damaged

Improper

Shipment) (Navy),

prescribed AFR

NAVSANDA

Publication

and

Force). Reporting and user of is Equipment encouraged. Changes U. to S. Manual Improvements. Report of errors, Form

omissions, individual 2028 to

recommendations

for improving this manual by the Reports should be submitted on DA DA Army Publications) Electronics Monmouth, and forwarded Command, Jersey 07703.

(Recommended

direct

Commanding

General,

ATTN:

AMSEL-MR-NMP-AD,

Fort

New

1-2.1

TM 11-6625-1576-15
Model 333A/334A Section I Paragraphs l-l to l-13

1-1. DESCRIPTION. 1-2. The Hewlett-Packard Models 333A and 334A Distortion Analyzers are solid state instruments for measuring distortion and ac voltages. The Models 333A and 334A include two control loops that automatically 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. A high im pedance detector which operates from 500 Kc to greater than 65 Mc provides the capability" of monitoring the distortion of the amplitude modulation on an rf carrier. 1-3. Distortion levels of O. 1% to 1OO% full scale are measured in seven ranges for any fundamental fre quency of 5 cps to 600 Kc. Harmonics are indicated up to 3Mc. The high sensitivity of these instruments requires only O. 3 v 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 fre quency range of 5 cps to 3 Mc (20 cps to 500 Kc for 300 pv range) and a voltage range of 300 pv to 300 v rms full scale. 1-5. The AM detector included in the Model 334A is a broadband dc restoring peak detector consisting of a semiconductor diode and filter circuit. AM distortion levels as low as O. 3% can be measured on a 3 v to 8 v rms carrier modulated 30% in the standard broadcast

band, and lower than 1% distortion can be measured at the same level of the carrier up to 65 Mc. 1-6. ACCESSORY FEATURES. 1-7. The accessory available with the 333A and 334A Distortion Analyzers is a voltage divider probe, -hpModel No. 1000lA. The features of the probe are: a. 10 megohms shunted by 10 pf, giving 10:1 attenuation. b. DC to 30 Mc bandwidth. c. 2% division accuracy. d. 600 v peak input. e. 5 ns rise-time. 1-8. OPTION. 1-9. Option 0l is a standard -hp- Model 333A or 334A with a special meter and meter amplifier, compensated to permit response to VU (volume units) characteristics. 1-11. Modifications

1-12, Specification C10-334A is a standard 334A Distortion Analyzer modified by placing the INPUT and OUTPUT terminals on the rear panel of the instrument. The rear terminals are binding post connectors and are in parallel with the front panel terminals. Due to the rear terminal leads, the shunt capacitance of the instrument is increased by 20pF .

1-3

TM 11-6625-1576-15
Model333A/334A Section II Paragraphs 2-1 to 2-19

SECTION

II

INSTALLATION
2-1. INTRODUCTION. 2-2. This section contains information and instructions necessary for the 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 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. 2-14. RACK INSTALLATION. 2-15. 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 ELA 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. 2-16. REPACKAGING FOR SHIPMENT. 2-17. The following paragraphs contain a general guide for repackaging of the instrument for shipment. Refer to Paragraph 2-18 if the original container is to be used; 2-19 if it is not.

2-5. POWER REQUIREMENTS. 2-6. The Model 333A/334A can be operated from any ac source of 115 or 230 volts (+10%), at 50- 1000 cps. With the instrument disconnected from the ac power source, move the slide (located on the rear panel) until the desired line voltage appears. The instrument can be battery operated by connecting two 28-50 V batteries (rated 80 milliamperes) to the battery terminal on the rear panel. Power dissipation is 10 watts maximum. 2-7. THREE-CONDUCTOR POWER CABLE. 2-8. To protect operating personnel, the National Electrical Manufacturers' Association (NEMA) recommends that the instrument panel and cabinet be grounded. All Hewlett-Packard instruments are equipped with a three -conductor power cable, which when plugged into an appropriate receptacle, grounds the instrument The offset pin on the power cable three-prong connector is the ground wire. 2-9. To preserve the protection feature when operating the instrument from a two-contact outlet, use a three-prong to two-prong adapter and connect the green pigtail on the adapter to ground. 2-10. INSTALLATION. 2-11 The Model 333A/334A is fully transistorized; therefore, no special cooling is required. However, the instrument should not be operated where the ambient temperature exceeds 55 C (191 F). 2-12. BENCH INSTALLATION. 2-1% The Model 333A/34A is shipped with plastic feet and tilt stand in place, ready for use as a bench instrument. 2-18. If original container is to be used, proceed as follows: a. Place instrument in original container if available.

b. Ensure that container is well sealed with strong tape or metal bands. 2-19. If original container is not to be used, proceed as follows: a. Wrap instrument in heavy paper or plastic before placing in an inner container. b. Place packing material around all sides of instrument 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," ""RAGILE," etc.

2-1

TM 11-6625-1576-15
Section III Figure 3-1 Model 333A/334A

Figure 3-1. Front and Rear Panel Description 3-0

TM 11-6625-1576-15
Model 333A/334A Section III Paragraphs-3-l to 3-15

SECTION III OPERATING
3-1. INTRODUCTION. 3-2. The Models 333A and 334A Distortion Analyzers measure total harmonic distortion from 5 cps to 600 Kc. Harmonics up to 3 Mc are included. The sharp elimination characteristics, >80 db, the low level of instrument induced distortion, and the meter accuracy of the 333A and the 334A result in accurate measurement of low level harmonic content in the input signal. 3-3. An RMS voltmeter is inherent in the 333A and 334A, The voltmeter provides a full scale sensitivity of 300 u volts rms (residual noise <25 u volts). The voltmeter frequency range is from 5 cps to 3 Mc except on the 0. 0003 volt range, which is from 20 cps to 500 Kc. 3-4. CONTROLS AND INDICATORS. 3-5. Figure 3-1 illustrates and describes the function of all front and rear panel controls, connectors, and indlcators. The description of each component is keyed to a drawing included within the figure. 3-6. ADJUSTMENTS OF MECHANICAL ZERO. 3-7. The procedure for adjustment of mechanical zero is given in Section V, Paragraph 5-25. 3-8. GENERAL OPERATING INFORMATION. 3-9. INPUT CONNECTIONS. 3-10. Signal source 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, battery operation is recommended to avoid ground loops. Another method for avoiding ground loops is by connecting only one instrument in a test setup directly to power line ground through a NEMA (threeprong) connector, Connect all other instruments to the power source through a three-prong to two-prong adapter and leave the pigtail disconnected. Both the 333A and 334A have a dc isolation of ±400 vdc from the external chassis with the shorting bar, (item 16 , Figure 3-1), disconnected. 3-11. VOLTMETER CHARACTERISTICS. 9-12. The RMS VOLTS markings on the meter face are based on the ratio between the average and effective (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 indication exists because the ratios of average to effective values are usually not the same in a com plexwave as in a sine wave. The amount of deviation depends on magnitude and phase relation between harmonics and fundamental frequency of the signal

INSTRUCTIONS
applied. Table 3-1 shows the deviation of the meter indication of a sine wave partly distorted by harmonic.. As indicated in the table, harmonic content of less than approximately 10% results in very small errors. Table 3-1 Effect of Harmonics on Voltage Measurements Meter Input Voltage True RMS Value Indication Characteristic Fundamental = 100 100 100 100 Fundamental +10% 100. s 2nd harmonic 100-102 Fundamental +20% 102 2nd harmonic Fundamental +50% 100-110 112 2nd harmonic 100.5 Fundamental +10% 96-104 3rd harmonic Fundamental +20% 102 94-108 3rd harmonic Fundamental +50% 3rd harmonic 112 90-116

NOTE This chart is universal in application since time errors are inherent in all average-responding type voltagemeasuring instruments. 3-13. In distortion measurements where the fundamental frequency is suppressed and the remainder of the signal is measured, the reading obtained on an averageresponding meter may deviate from the true total rms value. When residual wave contains many inharmonically related sinusoids, the maximum error in the distortion reading is about 11% low for distorilon levels below 10%. Measured Maximum Error Total Distortion In Meter Indication Distortion +0. 11 X O. 025 = 0.025 +0. 0027 = 2. 5% 0.0277 or 2.8% 0.00027 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 under most measurement conditions. 3-14. USE OF OUTPUT TERMINALS. 3-15. The OUTPUT terminals provide a O. 1 v rms 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 information

3-l

TM 11-6625-1576-15
Section III Paragraphs 3-16 to 3-22 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 the distortion that 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, capacitive loads greater than 50 pf should `be avoided to maintain the accuracy of meter readings. 3-16. OPERATING PROCEDURES. Model 333A/334A k. Position FUNCTION selector to DISTORTION, m. Adjust METER RANGE selector and frequency dial vernier control for minimum meter indication. n. Adjust COARSE and FINE BALANCE controls for further reduction of meter indication. Meter indication must be less than 10%of SET LEVEL indication. p. Position MODE switch to AUTOMATIC. r. Observe percentage of distortion indicated on meter. Meter indication is in conjunction with METER RANGE selector. For example, if meter indicates .4 and METER RANGE selector is on 1% position, distortion measured is 0.4%. NOTE RMS voltage of input signal being analyzed for distortion can be measured by positioning FUNCTION selector to VOLTMETER position. 3-20. DISTORTION MEASUREMENT IN PERCENT, MANUAL MODE. NOTE In MANUAL mode the accuracy of dis tortion measurements is affected by frequency stability of the input signal. An inaccuracy in distortion indications occure when the frequency drift of the input signal exceeds the bandwidth of the rejection curve. a. Perform steps a through n in Paragraph 3-19. b. Repeat steps m and n until no further reduction in meter- indication can be obtained. c. Observe percentage of distortion indicated on meter. 3-21. DISTORTION MEASUREMENT IN DB, AUTOMATIC MODE . a. Perform steps a through g of Paragraph 3-19. b. Adjust SENSITIVITY VERNIER control for 0 db meter indication. c. Perform steps j through 3-19. d. Observe meter indication for distortion in db. NOTE Distortion in db is obtained by algebraically adding meter indication to db indicated by METER RANGE selector: for example, If meter indicates -2 and METER RANGE selector is on -20 db position, distortion measured is -22 db. 3-22. DISTORTION MEASUREMENT IN DB, MANUAL MODE . NOTE Notes in Paragraphs 3-20 and 3-21 apply. a. Perform steps a through g of Paragraph 3-19. b. Adjust SENSITIVITY VERNIER control for O db meter indication.

3-17. The 333A and 334A Distortion Analyzers can be operated from an ac power source ( 115/230 volt) or a dc power source (+28 to +50 and -28 to -50 volt source). If a dc source is used, check the -25 v output. If necessary, adjust the power supply according to the procedures in Paragraph 5-27. 3-18. DISTORTION MEASUREMENT. 3- 19. DISTORTION MEASUREMENT IN PERCENT, AUTOMATIC MODE. a. Position FUNCTION selector to SET LEVEL. b. Position MODE switch to MANUAL. c. If fundamental frequency is 1 Kc or greater, position HIGH PASS FILTER SWITCH to IN. d. Rotate SENSITIVITY selector to MIN position. NOTE The bandwith of the SENSITIVITY selector is reduced in the two extreme CCW positions (positions used with an input signal greater than 30 v). e. Position METER RANGE selector to SET LEVEL 100%). f. Connect test leads from device under test to INPUT terminals.

REMOVE SHORTING STRAP BETWEEN FLOATING GROUND ~ AND CHASSIS GROUND (+) TERMINALS ON FRONT PANEL INPUT TERMINALS WHEN MEASURING DISTORTION BETWEEN TWO POINTS WHICH ARE BOTH ABOVE GROUND POTENTIAL. g. With SENSITIVITY VERNIER control max. CCW, position SENSITIVITY selector for meter indication greater than 1/3 full scale. NOTE If unable to adjust for full scale deflection which indicates input signal is below O. 3 volts, use manual mode and position METER RANGE selector downscale. Use this new position as the 100% SET LEVEL position, thus making the next range 30%, etc. h. Adjust SENSITIVITY VENIER control for full scale deflection. j. Position FRIQUENCY RANGE selector and frequency dial to fundamental frequency of input signal.

3-2

TM 11-6625-1576-15
Model 333A/334A c. Perform steps j through n of Paragraph 3-19. d. Repeat steps m and n until no further reduction n meter indication can be obtained. e. Observe meter indication for distortion in db. 3-23. DISTORTION MEASUREMENT OF AM RF CARRIERS. (334A Only) a. Set NORM - RF SET selector to RF SET. Section III Paragraphs 3-23 to 3-27 3-25. The 333A and 334A perform as general purpose AC Voltmeters when the FUNCTION selector is set to VOLTMETER position. NOTE With the FUNCTION selector in VOLTMETER position, the SENSITIVITY selector is disabled. a, Position METER RANGE selector to a range exceeding the value of the signal to be measured. b. Connect signal to INPUT terminals. c. Select a METER RANGE to give a reading as close to full scale as possible and observe meter indication. 3-26. OUTPUT TERMINALS. 3-27. In VOLTMETER or SET LEVEL position of the FUNCTION selector, the 333A/334A can be used as a low distortion, high gain, wideband preamplifier. A portion of the meter input (O. 1 v RMS output for full scale meter deflection) is provided at the OUTPUT terminal J2. In the DISTORTION position, the distortion is provided for monitoring purposes.

OBSERVE MAXIMUM INPUT VOLTAGES AS INDICATED ON REAR PANEL. b. Connect Input to RF INPUT on rear panel. c. Adjust SENSITIVITY VERNIER control for O db meter indication. d. Perform steps j through n of Paragraph 3-19. e. Refer to Paragraph 3-20 for manual measurement in percent. f. Refer to Paragraph 3-21 and 3-22 for automatic and manual measurement in db. -24. VOLTMETER MODE. NOTE If DBM measurements are to be made, the DB markings on the METER RANGE switch must each be lowered by 10. That is, the DB marking for the O. 3 v range becomes -10 DBM, 1 v range becomes O DBM, 3 v range becomes +10 DBM etc. If the other DB markings are used, the DBM readings will be 10 DBM high.

DO NOT EXCEED THE VOLTAGES LISTED BELOW TO PREVENT BLOWING FUSE F2: VOLTMETER.= -1 V RANGE AND BELOW, AND DISTORTION ANALYZER, MODE-MAXIMUM SENSITIVITY. 1. 300 V ABOVE 100 CPS 2. 50 V ABOVE 1 KC IF LOW FREQUENCIES ARE NOT TO BE MEASURED, Cl MAY BE REPLACED WITH A SMALLER CAPACITOR, AND THE VOLTAGE LIMITS OF F2 MAY BE RAISED ACCORDINGLY.

3-3

TM11-6625-1576-15
Section IV Figure 4-1 Model 333A/334A

Figure

4-1.

Block

Diagram

TM 11-6625-1576-15
Model 333A/334A Section IV paragraphs 4-1 to 4-12

SECTION IV THEORY OF OPERATION
4-1. OVERALL DESCRIPTION. 4-2. Models 333A and 334A Distortion Analyzers include an impedance converter, a rejection amplifier, a metering circuit, and a power supply, The Model 334A also contains an AM detector. A block diagram of the instruments is shown in Figure 4-1. The im pedance converter provides a low noise input circuit with a high input impedance independent of source impedance placed at the INPUT terminals. The rejection amplifier rejects the fundamental frequency of an 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, M 1. The AM detector (Model 334A only) detects the modulating signal from the RF carrier and filters any RF components from the modulating signal before it is applied to the impedance converter circuit. 4-3. BLOCK DIAGRAM DESCRIPTION. 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, S1, and the one megohm attenuator, The one megohm attenuator, a voltage divider network provides 50 db attenuation in 10 db steps. The desired level of attenuation is selected by the SENSITIVITY selector, S2. The impedance converter provides an impedance conversion and unity gain between the instrument INPUT terminals and the input of the rejection amplifier. 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 reading on the meter for any voltage level at the input of the instrument. With the FUNCTION selector in the SET LEVEL position, a ground is applied in the Wien bridge circuit to allow a signal reference level to be set up on the meter. With the FUNCTION selector in the DISTORTION position, the Wien bridge is used as an interstate coupling network between the preamplifier and bridge amplifier. The Wien bridge is tuned and balanced to reject the fundamental frequency of the applied input signal. Two automatic control loops consisting of two phase detec tors, lamp drivers, lamps, and photocells provide fine tuning and balance in the AUTOMATIC MODE. The remaining frequency components are applied to the bridge amplifier and are measured as distortion by the metering circuit. Negative feedback from the bridge amplifier to the preamplifier narrows the rejection response of the Wien bridge. The output of the rejection amplifier is applied to the metering cir cuit 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 deflectlon. The metering circuit sensitivity is increased to 300 u V for full scale deflection on the 300 pv range. The metering circuit provides a visual indication of the distortion level of the input signal. In addition to the visual indication provided by the meter, the OUTPUT terminals provide a means of monitoring the distortion components. 4-6. DISTORTION MEASUREMENT IN AM CARRIERS. 4-7. The Model 334A Distortion Analyzer contains an AM detector circuit for measuring envelope distortion in AM carriers. The input signal is applied to the input 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 distortion measuring mode operation. 4-8. VOLTMETER OPERATION. 4-9. 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 attenuation ratio is used in the .0003 to .3 VOLTS position of the METER RANGE selector S3, and the 1000:1 attenuation ratio is used in the 1 to 300 VOLTS posit ions. With the FUNCTION selector 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 selector). Metering circuit sensitivity is increased from 1 mv for full scale deflection to 300 uv on the 300 uv 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. 4-10. SCHEMATIC THEORY. 4-11. IMPEDANCE CONVERTER CIRCUIT. 4-12. The input signal to the distortion analyzer is applied to the impedance converter circuit (refer to Figure 6-2) through the 1:1 and 1000:1 attenuator S3R12 in the voltmeter mode of operation and through the one megohm attenuator S2R1 through S2R6 in the distortion mode of operation. Capacitive dividers S2C10 through S2C 10 in the attenuator keep the frequency response flat. The impedance converter is a low distortion, high input impedance amplifier circuit wit h gain independent of the source impedance placed at the INPUT terminals. Instrument induced distortion of the signal being measured is minimized by keeping the input impedance and the gain of the impedance converter linear. The input impedance is kept linear by use of local positive feedback from the source of A2Ql to the gate of A2Q1 and to the protective diodes A2CR2 and A2CR3. Thus signals with large source impedance 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

4-1

TM11-6625-1576-15
Section IV Paragraphs 4-13 to 4-25 and Figure 4-2 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. 4-13. The bias points of the transistors in the impedance converter are selected to minimize instrument induced distortion. A2Q 1, an extremely low noise, high impedance field effect transistor, is the major component that makes linearity of the Impedance converter independent of the signal source impedance. 4-14. REJECTION AMPLIFIER CIRCUIT. 4-15. The rejection amplifier circuit (see Figures 6-3 and 6-6) consists of the preamplifier (A3Q1) thru A3Q3), the Wien bridge resistive leg and auto control loop (A5Q1 thru A5Q9 with associated lamp and photocell), the reactive leg and auto control loop (A5Q10 thru A5Q 18 with associated lamp and photocell), and the bridge amplifier (A3Q4 thru A3Q6). 4-16. PREAMPLIFIER CIRCUIT. 4-17. 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 A3R1O and A3R11 is applied to the junction of A3R2 and A3C2 to establish the operating point for A3Q1. 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. 4-18. WIEN BRIDGE CIRCUIT. 4-19. 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, S1, 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 applicable frequency range, and tuning the capacitors C4A through C4D. The bridge circuit is balanced by adjusting 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. 4-20. When the Wien bridge is not tuned exactly to the frequency to be nulled, a portion of the fundamental 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 proportional to the magnitude of the tuning error of either or both legs of the bridge. Model 333A/334A

Figure 4-2. Bridge Waveforms 4-21. Figure 4-2a is a sinusoid input to the 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. 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 90° out of phase with the resistive signal. 4-22. 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 which 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 insensitive to input differing from the reference by 90° . 4-23. 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. 4-24. 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 causes resistance changes in photocells which form part of the Wien bridge. 4-25. Refer to Figure 4-3 for the phase relationship of the bridge error signal and reference voltage at the base of A5Q4. The shaded portions of the error signals (b and c) indicate that part of the error signal which contributes to the dc lamp control voltage. As indicated in d, any error signal that is 90° out of phase with the reference does not affect the dc lamp control voltage.

4-2

TM 11-6625-1576-15
Model 333A/334A 4-26. The operation of the reactive branch control loop is similar to that of the resistive branch. The phase delay circuit (Figure 6-6), A5Q15, A5Q16, S4AF and S4C1 through S4C5, shifts the reference voltage 90º, as shown in Figure 4-3f. This makes the detector A5Q12 sensitive to components of the bridge error signal that are 90° out of phase (g and h). The output of the lamp driver, Q14, 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 frequency ranges. A6DS2 will become brighter, and lower the Section IV Paragraphs 4-26 to 4-27 and Figure 4-3 resistance of A6V2 through A6V5, making variation in resistance less than on the two lower ranges. However, 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. 4-27. Any error signal that is not an integral multiple of 90 is the result of the reactive leg of the bridge . being detuned, and the resistive leg being unbalanced. For example, an error signal that is 45º out of phase (Figure 4-3e and j) will result in outputs from both detectors to tune the bridge and reject the fundamental.

Figure 4-3. Reference and Error Phase Relationship

4-3

TM 11-6625-1576-15
Section IV Paragraphs 4-28 to 4-35 and Figures 4-4 to 4-5

Figure 4-4. Wien Bridge Circuit and Rejection Characteristics positive half of the signal will be passed, and if it is 4-28. When the bridge circuit is tuned and balanced, out of phase, the negative half will be passed. the voltage and phase of the fundamental, which appears at junction of the series reactive leg (S4R1, 3, 5, 7, 4-32. The normal working voltage at TP3 is between or 9 and C4A/B) and the shunt reactive leg (S4R11, 0 and -1 volt. The dc output of the filter network 13, 15, 17, or 19, and C4C/D), is the same as at the causes the voltage at TP3 to go in a positive direction midpoint of the resistive leg (A3R12 and A3R14). When (toward zero) for in phase error signals, and in a these two voltages are equal and in phase, the fundanegative direction (toward -1 v) for out of phase error mental frequency will not appear at the drain of the signals. The change in base voltage is then amplified field effect transistor A3Q4. For frequencies other by A5Q5 and lamp driver A5Q6. This will change the than the fundamental, the reactive leg of the Wien brilliance of lamp A6DS1, which will vary the resisbridge offers various degrees of attenuation and phase tance of A6V1 in the direction necessary to balance shift which cause a voltage at the output points of the the resistive leg of the bridge. bridge. This difference voltage between the reactive leg and resistive leg is amplified by A3Q4, A3Q5, and A3Q6. Figure 4-4 illustrates 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 course 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 reference voltage is taken from R6 at the input to the rejection 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 A5Q1. It is amplified by A5Q2 and A5Q3 and coupled to the detector A5Q4. 4-30. Refer to Figure 4-5 simplified 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 collector 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 AQ5. If the signal from A5Q2 is in phase with the reference, the

Figure 4-5. Auto Control Loop Detector 4-33. When the FUNCTION selector is set to the VOLTMETER or SET LEVEL position, the junction of the series and shunt reactive branches of the Wien bridge is connected to circuit ground through R19 by S1BF which disables the frequency rejection characteristic of the bridge circuit. With the bridge circuit disabled, the rejection amplifier circuit provides 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 reference. 4-34. BRIDGE AMPLIFIER CIRCUIT. 4-35. The bridge amplifier circuit consists of three stages of amplification, A3Q4 through A3Q6. The

4-4

TM 11-6625-1576-15
Section IV Paragraphs 4-36 to 4-45 and Figure 4-6

Figure 4-6. Rejection Amplifier Block Diagram and Typical Frequency Rejection Characteristic the calibration network on the 300 Pv range to extend first stage of amplification, A3Q4, is a field effect the passband of the amplifier. transistor which amplifies the difference signal between the gate and the source. The field effect transistor 4-42. METER AMPLIFIER CIRCUIT. is selected for maximum noise performance with the high impedances of the Wien bridge circuit. The signal 4-43. The meter amplifier circuit consists of a five from the drain is applied to the two stage feedback amstage amplifier circuit, A2Q5 through A2Q9, which plifier A3Q5 and A3Q6. The output of A3Q6 is coupled develops the current for full scale meter deflection. to the meter circuit by the post attenuator S3R1 through Negative dc feedback from the emitter circuit of S3R11. Negative feedback from the output of the bridge A2Q8 is applied to the base of A2Q5 to stabilize the amplifier is applied to the preamplifier circuit to nardc operating point of the meter amplifier circuit and row the frequency rejection characteristic. It can be to minimize the tendency for dc drift due to ambient noted from the rejection characteristic (refer to Figure temperature changes. A2R51 and A3CR8 are electric4-4) for the bridge that the rejection of harmonic voltally in the circuit only when the meter circuit is overages is not constant. Typically the second harmonic loaded. When the voltage on the emitter of A2Q9 beis attenuated several db more than the third harmonic comes abnormally large during an overload, A2CR8 and the third more than the fourth. The result of the breaks down and provides a lower resistance charging negative feedback is illustrated by the rejection characpath for A2C15 which reduces the transient recovery teristic shown in dashed lines on the attenuation and time of the meter circuit. Negative ac feedback is phase characteristic of Figure 4-4. Figure 4-6 shows applied from the collector circuit of A2Q9 to the emita simplified block diagram of the rejection amplifier ter circuit of A2Q5. This feedback is used to ensure with the typical frequency-rejection characteristic. flat frequency response, to improve linearity, and to Refer to Figure 4-7, Bandwidth Versus Null Depth for reduce the effect of variation of transistor parameters further detail on the rejection characteristic. with environmental changes. In this manner, the calibration of the instrument is made dependent on 4-36. HIGH PASS FILTER. high quality passive components. 4-37. The HIGH PASS FILTER (see Figure 6-3) is normally used when the fundamental of the input signal 4-44, METER RECTIFIER CIRCUIT. is greater than 1 Kc. In the voltmeter mode of opera4-45. The meter rectifier is connected in a bridge type tion, the filter is not used. In the SET LEVEL and of configuration with a diode in each upper branch and DISTORTION position of the FUNCTION switch the a dc milliammeter connected across the midpoints of filter presents >50 db attenuation to 50 or 60 cycle the bridge. The simplified meter rectifier is illuhum components, but offers no attenuation to frequenstrated in Figure 4-8. The generator represented by cies over 1 Kc. The filter assembly, A7, consists of A2Q5 through A2Q9 with the internal impedance RO A7C1, A7C2, and A7L1. The filter can be inserted provides the meter, M1, with current for full scale or bypassed by the HIGH PASS FILTER switch, S9. deflection and develops a voltage across the calibration 4-38. METER CIRCUIT. network which closes the ac feedback loop. Capacitors A2C27 and A2C28 are used as coupling capacitors for 4-39. The meter circuit (refer to Figure 6-4) consists the ac feedback loop, output signal to the OUTPUT of the post attenuator, the meter amplifier circuit, connector, and the bridge error signal to the input of and the meter rectifier circuit. the automatic fine tuning loops. The mechanical inertia 4-40. POST ATTENUATOR. of the meter and A2C26 prevents the meter from reTherefore, sponding to individual current pulses. 4-41. The post attenuator, S3R1 through S3R11, is a the meter indication corresponds to the average value series of resistive networks which attenuate the input of the current pulses rather than the peak value. The signal in 10 db steps. The attenuator is used in conmeter is calibrated to indicate the rms value of a sine junction with either the input sensitivity attenuator or wave. Resistor A2R45 impresses a fixed bias across the 1000:1 attenuator to limit the signal level to the diodes A2CR6 and A2CR7 (biasing them close to the meter amplifier to 1 mv for full scale deflection on barrier voltage) to make the meter circuit response all ranges from 1 mv to 300 v full scale. The meter linear to large variations in signal amplitude. The circuit sensitivity is increased to 300 uv for full scale linearity of this type of circuit is also increased by deflection on the 300 uV range by switching resistors including the meter circuit in the overall feedback A2R29 and A2R30 into the calibration network. Resisloop. tor A2R41 and capacitor A2C29 are also switched into

4-5

TM 11-6625-1576-15
Section IV Figure 4-7 Model 333A/334A

Figure 4-7. Bandwidth Versus Null Depth

4-6

TM 11-6625-1576-15
model 333A/334A Section IV Paragraphs 4-46 to 4-52 and Figure 4-8

Figure 4-8. Simplified 4-46. POWER SUPPLY CIRCUIT. 4-47. The power supply circuit (refer to Figure 6-5) consists of a +25 voIt series regulated supply and a -25 volt series regulated supply which is the reference supply for the +25 volt supply. 4-48. The -25 volt regulated supply is of the conventional series regulator type. The amplifier A1Q5 is used to increase the loop gain of the circuit, thus improving voltage regulation. The positive feedback applied to the junction of A1R1l and A1R12 is used to further improve the line frequency suppression of the circuit. 4-49. The +25 volt regulated supply is of the conventional series regulator type and operates the same as the -25 volt regulated supply.

Metering Circuit 4-50. Diodes A1CR5 and A1CR6 are coupling and protection diodes for external battery supplies. The diodes protect the series regulator circuits from application of incorrect polarity at the battery input terminals. The diodes also protect external batteries from being charged when the ac power is being used with batteries connected to the battery terminals. 4-51. RF DETECTOR CIRCUIT. (334A only) 4-52. The RF detector circuit consists of a rectifier A4CR1 and filter circuit shown on the schematic diagram of Figure 6-2. The RF signal is applied to the circuit through the RF INPUT connector on the rear panel. The rectifier diode A4CR1 recovers the modulating signal from the RF carrier and the filter circuit removes any RF components before the signal is ap pIied to the impedance converter circuit through the NORM -RF DET switch, S7.

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TM 11-6625-1576-15
Section V Table 5-1 Table 5-1. Test Equipment Required Model 333A/334A

5-0

TM 11-6625-1576-15
Model 333A/334A Section V Paragraphs 5-l to 5-9 and Figure 5-1

SECTION V MAINTENANCE
5-1. INTRODUCTION. 5-2. This section contains maintenance and service information for the 333A and 334A Distortion Analyz ers. Included are Performance Checks, Adjustment and Calibration Procedures, and Troubleshooting Techniques. 5-3. TEST EQUIPMENT REQUIRED. 5-4. Test equipment used in the calibration of the 333A and 334A is given in Table 5-1, Test Equipment Required. This table lists the type of equipment to be used, required characteristics, and recommended commercially available test equipment. 5-5. PERFORMANCE CHECKS. 5-6. The Performance Checks are in-cabinet procedures that can be used to verify instrument performance, These procedures can be used for periodic maintenance, to check specifications after a repair, or for incoming quality control inspection. 5-7. Performance Checks for both the 333A and 334A are provided. The performance checks are applicable to both instruments except where noted in paragraph heading. 5-8. The Performance Checks are performed with the ac power cord connected to nominal line voltage (115 v/230 V) 50 to 1000 cps, MODE SWITCH to MANUAL, HIGH PASS FILTER to OUT, and NORM RF DET switch to NORM, unless otherwise specified. Selector positions for the SENSITIVITY Selector will be referred to as follows: MIN=Position 1, next step-Position 2, etc, to Max= Position 6. 5-9. FUNDAMENTAL REJECTION CHECK a. Connect 33lA/332A as shown in Figure 5-1. b. Set Distortion Analyzer controls as follows: FUNCTION Selector . . . . . . VOLTMETER METER RANGE Selector . . . . . . . 1 VOLT FREQUENCY RANGE Selector . . . . . . X1OO Frequency Dial . . . . . . . . . . . . . . . 50 Set filter (White Instr Lab Model 2640) . . . . . . . . . . . . . . . . . . . . . . . . .5Kc c. Set Test Oscillator (-hp - Model 651A) frequencv to 5 KC and adjust amplitude for indication of 1.0 volt on Distortion Analyzer meter. d. Switch Distortion Analyzer FUNCTION to SET LEVEL. Switch METER RANGE to O. 3 VOLTS. Adjust SENSITIVITY controls for full scale meter indication. e. Set Wave Analyzer controls (-hp - Model 302A) as follows: SCALE VALUE . . . . . . . . . . RELATIVE MAX INPUT VOLTAGE . . . . . . . . ...1 RANGE . . . . . . . . . . . . . . 0 DECIBELS MODE SELECTOR . . . . . . . . . .NORMAL f. Adjust Wave Analyzer FREQUENCY controls for maximum meter reading (approximately 1 Kc). g. Adjust Wave Analyzer REF ADJUST for O db meter indication. NOTE If the range of the REF ADJUST control is insufficient to set meter to O db reference, adjust the Distortion Analyzer SENSITIVITY VERNIER control slightly to set reference. h. Switch Distortion Analyzer FUNCTION to DISTORTION. Adjust BALANCE controls and FREQUENCY dial for null indication on Distortion Analyzer meter. Reduce Distortion Analyzer METER RANGE selector setting as necessary to maintain deflection on meter scale. j. After achieving null indication on Distortion Analyzer meter, observe Wave Analyzer mete r and continue to adjust for a null indication. Reduce Wave Analyzer RANGE setting as necessary to maintain deflection on meter scale. NOTE The Distortion Analyzer OUTPUT is a O to O. 1 volt signal representing a percentage of full scale, regardless of RANGE

Figure 5-1. Test Setup for Fundamental Rejection Check

5-1

TM 11-6625-1576-15
Section V Paragraphs 5-10 to 5-11, Figure 5-2 and Table 5-2 setting. Each decrease of the RANGE switch represents 10 db fundamental rejection. Therefore, the total fundamental rejection is the sum of the Wave Analyzer reading and the 333A/334A indication. k. The Distortion Analyzer METER RANGE setting plus the Wave Analyzer RANGE setting plus the two meter indications shall total more than -80 db. 5-10. SECOND HARMONIC ACCURACY CHECK. a. Connect Test Oscillator (-hp-Model 651A) 600 output to Distortion Analyzer * b. Set Distortion Analyzer controls as follows: FUNCTION Selector . . . . . . . SET LEVEL FREQUENCY RANGE . . . . . . . . . . . X1 Frequency Dial . . . . . . . . . . . . . . .20 METER RANGE Selector . . . . . . . . . 0 DB c. Set Test Oscillator controls as follows: FREQUENCY RANGE . . FREQUENCY Dial. . . . OUTPUT ATTENUATOR AMPLITUDE . . . . . . . (-hp- Model 651A) . . . . . . . . . . . . X10 . . . . . . . . 2 . . . . 1.0 VOLTS . . . . . . l Volt Model 333A/334A j. Repeat steps a through h at the frequency settings indicated in Table 5-2. The meter readings shall change within the limits specified. Table 5-2. Second Harmonic Accuracy Check

5-11. DISTORTION INTRODUCED BY INSTRUMENT CHECK AND AUTOMATIC CONTROL LOOP OPERATION. a. Connect 333A/334A as shown in Figure 5-2. b. Set Distortion Analyzer controls as follows: FUNCTION Selector . . . . . . . SET LEVEL SENSITIVITY Selector . Position 1 step CCW from Full CW position SENSITIVITY VERNIER Control . . full CCW METER RANGE Selector . . . . . . . . . . 0 db FREQUENCY RANGE Selector . . . . . . . Xl Frequency Dial . . . . . . . . . . . . . . .5 c. Set oscillator for approximately 1 volt output at 5 cycles. d. Set filter box for 5 cycles. e. Adjust oscillator amplitude for an indication of +2 db on the Distortion Analyzer meter. f. Switch Distortion Analyzer FUNCTION selector to DISTORTION. Adjust frequency dial and BALANCE controls for a null meter indication. (If reading is in lower 1/3 of meter scale, decrease METER RANGE selector setting. ) g. The meter indication at "null" shall be at least -8 db on the -60 db METER RANGE which is equivalent to -70 db. Note reading.

d. Adjust Distortion Analyzer SENSITIVITY controls for a meter reading of O db. e. Switch Distortion Analyzer FUNCTION selector to DISTORTION. Adjust Frequency dial and BALANCE controls for a null indication on meter. f. Switch Distortion Analyzer FUNCTION selector to SET LEVEL. g. Adjust Test Oscillator frequency to 40 cps. Adjust AMPLITUDE control for a O db indication on the Distortion Analyzer meter. h. Switch Distortion Analyzer FUNCTION selector to DISTORTION. The meter reading shall not change more than ±0. 6 db.

Figure 5-2.

Instrument Induced Distorition and Automatic Control Loop Test Setup

5-2

TM 11-6625-1576-15
Model 333A/334A h. Set METER RANGE to O. 01 volt RANGE and offset frequency dial to a lower reading so that meter cads full scale. Set MODE switch to AUTOMATIC id note distortion level. Distortion level should be within +3 -O db of manually nulled reading. j. Set MODE switch to MANUAL (and meter range to o. 01). Offset frequency dial past null to a higher dial reading so that meter reads full scale. Return MODE switch to automatic. Distortion reading should be within +3 -O db of manually nulled reading obtained in step g of this paragraph. k. Set MODE switch to MANUAL and adjust fre quency dial for null. Adjust COURSE BALANCE Control CW with METER RANGE set at 0. 01 so that meter reads full scale. Return MODE Switch to AUTOMATIC. Distortion reading should be within +3 -0 db of manually nulled reading obtained in step g of this paragraph. m. Set MODE switch to MANUAL and METER RANGE to O. 01. Adjust COARSE BALANCE Control CCW so that meter reads +2 db. Set Mode switch to Automatic. Distortion reading should be within +3 -O of manually nulled reading obtained in step g of this paragraph. n. Repeat steps b through m with controls set as indicated in Table 5-3. Except in steps j thru m use METER RANGE setting of O. 03 to obtain +2 db reading when detuning Frequency Dial and COARSE BALANCE Control to verify automatic control loop operation. Table 5-3. Distortion Introduced By Instrument Check Section V Paragraph 5-12, Table 5-3, and Figure 5-3 NOTE From 5 cps to 10 cps the FREQUENCY dial may be as much as 3% low. In this test the dial is held constant, and the input frequency is varied and monitored. If the dial is low, the input frequency at null will be high. If the period of the input frequency is measured, it will be low when the dial is low. From 200 Kc to 600 Kc the dial may be as much as 8% high, Consequently, a low frequency reading at null would indicate that the dial is reading high. b. Set Distortion Analyzer controls as follows: FUNCTION Selector . . . . . . . SET LEVEL METER RANGE Selector . . . . . . . . 0 DB SENSITIVITY Selector . . . . . . . . . . MIN. FREQUENCY RANGE Selector . . . . . .Xl Frequency Dial . . . . . . . . . . . . . . . .5 c. Set Test Oscillator controls (-hp- Model 203A) as follows: FREQUENCY RANGE . . . . . . . . . . . X1 FREQUENCY DIAL . . . . . . . . . . . . . . 5 OUTPUT ATTENUATOR . . . . . . 1.0 VOLT d. Set Electronic Counter controls (-hp - Model 5532A) as follows: SENSITIVITY . . . . . . . . . . 3 VOLTS RMS Function Switch. . . . . 1 PERIOD AVERAGED DISPLAY . . . . . . . . . . . . . . Fu1l CCW e. Adjust Test Oscillator AMPLITUDE control for a full scale indication on the Distortion Analyzer meter. f. Switch Distortion Analyzer FUNCTION selector to DISTORTION. g. Adjust Test Oscillator FREQUENCY DIAL for a null indication on the Distortion Analyzer meter. (If reading is in lower 1/3 of meter scale, decrease METER RANGE selector setting, ) h. Adjust Distortion Analyzer BALANCE controls for a null indication on the meter. Repeat steps g and h until a null is reached.

5-12. FREQUENCY CALIBRATION ACCURACY CHECK. a. Connect 333A/334A as shown in Figure 5-3.

Figure 5.-3. Test Setup for Frequency Calibration Accuracy Check

5-3

TM11-6625-1576-15
Section v Paragraphs 5-13 to 5-16 and Table 5-4 Model 333A/334A

j. The Electronic Counter shall indicate the period of 5 cps -3%, i. e. 194 to 200 msec. k. Repeat steps b through h with controls set as indicated in Table 5-4. The Electronic Counter shall indicate the Test Oscillator output frequencies within the limits indicated. 5-13. INPUT RESISTANCE CHECK a. Connect Test Oscillator (-hp- Model 651A) 600 output to Distortion Analyzer INPUT terminals. b. Set Distortion Analyzer controls as follows: FUNCTION Selector . . . . . . VOLTMETER SENSITIVITY Selector . . . . . . . . . MAX. SENSITIVITY VERNIER Control . . . . . MIN. METER RANGE Selector. . . . . . . 1 VOLT c. Set Test Oscillator controls as follows: FREQUENCY RANGE . . . . . . . . . . X10 FREQUENCY Dial . . . . . . . . . . . . . 10 OUTPUT ATTENUATOR . . . . . . 1.0 VOLT d. Adjust Test Oscillator AMPLITUDE control for an indication of 1.0 volt (Ein) rms on the Distortion Analyzer meter. e. Connect a 100 K (Ra) ±1. 0%, 1/2 watt, fixed carbon film resistor in series with the Distortion Analyzer INPUT. Note the Distortion Analyzer meter reading (Eo). f. Calculate the Distortion Analyzer input resistance using the following formula:

e. Set Distortion Analyzer controls as follows: . FUNCTION Selector . . . . . .DISTORTION SENSITIVITY Selector . . . . . . . . . . MIN. METER RANGE Selector . . . . . . . VOLTS f. Measure Capacitance at each SENSITIVITY selector setting of the Distortion Analyzer. The L - C meter shall indicate less than 60 pf on each of these settings. 5-15. MINIMUM INPUT LEVEL CHECK. a. Connect Test Oscillator (-hp- Model 651A) 600 output to Distortion Analyzer INPUT terminals l Terminate test oscillator with 600 ±1% 1/2 w resistor. b. Set Distortion Analyzer controls as follows: FUNCTION Selector . . . . . . . VOLTMETER METER RANGE Selector . . . . . . .3 VOLT SENSITIVITY Selector . . . . . . . . . MIN. SENSITIVITY VERNIER . . . . . . . . , CCW c. Set Test Oscillator for 20 cps. d. Adjust Test Oscillator amplitude for a Distortion Analyzer- meter indication O. 3 volts. e. Switch Distortion Analyzer FUNCTION selector to SET LEVEL. f. Switch SENSITIVITY selector to MAX and VERNIER to full CW. The SENSITIVITY controls shall have sufficient range to give a full scale meter reading. 5-16. DC ISOLATION CHECK. a. Connect 333A/334A as shown in Figure 5-4.

g. The input resistance shall be 1 M ±5%. h. Switch FUNCTION selector to Distortion and calculate the input resistance in this position. It shall be 1 M ±5%. 5-14. INPUT SHUNT CAPACITANCE CHECK. a. Set Distortion Analyzer controls as follows: FUNCTION Selector . . . . . . . VOLTMETER METER RANGE Selector . . . . . . . 1 VOLT b. Connect an L - C meter to the 333A/334A and measure the input capacitance. c. The L - C meter shall indicate less than 30 pf. d. Switch the Distortion Analyzer on the 0. 3 range and measure capacitance. Meter shall indicate less than 60 pf.

REMOVE SHORTING BARS BETWEEN POWER LINE GROUND TERMINALS ON DISTORTION ANALYZER INPUT TERMINALS AND FUNCTION GENERATOR OUTPUT TERMINALS. b. Set Distortion Analyzer controls as follows: FUNCTION Selector . . . . . .VOLTMETER METER RANGE Selector . . . . . . . 1 VOLT c. Apply ac power to dc power supply and set for 400 v. Set Power SuppIy controls but do not apply dc to the Distortion Analyzer. d. Set Function Generator for 1 Kc and adjust the amplitude control for an indication of 0. 9 on the Distortion Analyzer meter.

5-4

TM 11-6625-1576-15
Model 333A/334A Section V Paragraphs 5-17 to 5-18 and Figures 5-4 to 5-5

Figure 5-4. DC Isolation Check Test Setup g. Check the Distortion Analyzer voltmeter tracke. Apply the 400 v dc to the Distortion Analyzer. ing at 0. 1 volt increments from 0. 1 volt to 1 volt. The There shall be no change in the indication on the Dis voltmeter tracking accuracy shall be within ± 1%. tortion Analyzer meter, or any indication on the ammeter of the power supply. h. Repeat steps d through g with the variable Line Transformer set to 105 v & 125 v. 5-17. VOLTMETER ACCURACY CHECK 5-18. HIGH PASS FILTER CHECK a. Connect Voltmeter Calibrator (-hp- Model 738B) a. Connect the 333A/334A as shown in Figure 5-6. and Variable Line Transformer (Superior Type UC1M) to Distortion Analyzer as shown in Figure 5-5. Reb. Set Distortion Analyzer controls as follows: move shorting bar between power line ground and cirFUNCTION Selector. . . . . . . SET LEVEL cuit ground terminals. METER RANGE Selector . . . . SET LEVEL b, Set Variable Line Transformer for 115 v output. HIGH PASS FILTER switch . . . . . . . In SENSITIVITY Selector . . . . . . . . Position 5 c. Set Distortion Analyzer FUNCTION Selector to VOLTMETER. SENSITIVITY VERNIER . . . . . . . CCW d. Set voltmeter calibrator for 400 cps output. c. Adjust frequency response test set to 5Kc and set output amplitude to obtain a zero db indication on e. Check the Distortion Analyzer voltmeter full Distortion Analyzer. scale readings on all ranges against the appropriate rms input voltages from the voltmeter calibrator. The d. Adjust frequency response test set meter to set voltmeter accuracy shall be within ±2%, level reference. f. Set the Distortion Analyzer METER RANGE e. Set frequency response test set to 1 Kc and adjust selector to 1 VOLT range. output amplitude so that test set meter reads set leveI.

Figure 5-5. Voltmeter Accuracy check Test Setup

5-5

TM 11-6625-1576-15 Section V
Paragraphs 5-19 to 5-21, Figure 5-6 and Table 5-5 Model 333A/334A

f. Reading on Distortion Analyzer shall be within O. 5 db of zero db setting. g. Set frequency response test set to 60 cps and adjust the output amplitude so that test set meter reads set level. h. Switch Distortion Analyzer Meter Range to 0. 003 volt range, j. Reading should be > -40 db. 5-19, VOLTMETER FREQUENCY RESPONSE CHECK. a. Connect Distortion Analyzer to test equipment as shown in Figure 5-6. b. Set Distortion Analyzer controls as follows: FUNCTION Selector . . . . . . . .VOLTMETER METER RANGE Selector. . . . . .0.01 VOLTS c. Set the Variable Line Transformer output to 115 v. d. Adjust the Oscillator for an indication of O. 9 at 400 cps on the Distortion Analyzer meter. e. Adjust the Frequency Response Test Set METER SET control to SET LEVEL indication on the meter. f. Switch the Oscillator RANGE switch to X 1 and set the Frequency Dial to 5. g. Readjust the Oscillator AMPLITUDE control until the Frequency Response Test Set meter indicates SET LEVEL. h. The Distortion Analyzer meter shall indicate between 0.855 and 0.945 (±5%). j. Set the Oscillator to the frequencies listed in Table 5-5. Repeat step g after each setting. The Dis tortion Analyzer meter shall indicate 0.9 ± the tolerances indicated. k. Switch the Frequency Response Test Set RANGE SELECTOR to the 1-3 Mc position. Set the FREQ. TUNING dial to the frequencies listed in Table 5-5. Adjust the Frequency Response Test Set AMPLITUDE control until the meter indicates SET LEVEL after each frequency setting. The Distortlon Analyzer meter shall indicate 0.9 ± the tolerances indicated.

n. Repeat steps b through k with the Variable Line Transformer set to 105 v and 125 v. Table 5-5. Voltmeter Frequency Response Check

5-20. RESIDUAL NOISE CHECK a. Connect a shielded 600 resistor across the Distortion Analyzer INPUT terminals. (See Figure 5-7 for details on constructing shielded load. ) Secure the shorting bar between the power line ground and circuit ground terminals. b. Set Distortion controls as follows: FUNCTION Selector . . . . . . . VOLTMETER METER RANGE Selector . . . . 0.0003 VOLTS c. The meter shall indicate less than 25 µ volts. d. Remove the 600 resistor. Connect a shielded 100 K ohm resistor across the INPUT terminals. (See Figure 5-7 for details on constructing shielded load. ) e. The meter shall indicate less than 30 µ volts. 5-21. AM DETECTOR CHECK (Model 334A only). a. Connect Signal Generator (hp- Model 606A) 50 RF OUTPUT to Distortion Analyzer RF INPUT. b. Set Distortion Analyzer controls as follows: FUNCTION Selector . . . . . . . SET LEVEL NORM-RF DET Switch . . . . . . . RF DET METER RANGE Selector . . . . . . . . . 0 DB FREQUENCY RANGE Selector . . . . . X100 FREQUENCY Dial . . . . . . . . . . . . . 10

5-6

TM 11-6625-1576-15
Model 333A/334A Section V Paragraphs 5-23 to 5-27, Figure 5-7 and Table 5-6 No. 1 2 3 4 4 5 6 7 8 Description Connector, male Connector, male w/insulator Lug, terminal 90° Resistor, 100 K , 1/2 W , 5% metal film Resistor, 600 K , 1/4 w, O. 5% metal film Washer, int. lock Spacer, 6-32 threaded Shield Screw, bind. head, 6-32 x 1/4 in -hp- Part No. 1251-0174 1251-0175 0360-0042 0758-0053 0757-1037 2190-0007 0380-0058 1251-1073 2470-0001

#

Figure 5-7. Shielded Load Assembly switch to MANUAL, HIGH PASS FILTER to OUT, and c. Set Signal Generator controls as follows: NORM RF DET switch to NORM, unless otherwise FREQUENCY. . . . . . . . . . . . . . . l Mc specified. MODULATION SELECTOR . . . . . . . EXT ATTENUATOR/VERNIER . . . . . 3.O VOLTS 5-25. METER MECHANICAL ZERO SET. Modulate Signal Generator output 30% with a 1000 5-26. The meter is properly zero-set when the pointer cps signal using a 203A Function Generator or rests over the zero calibration mark on the meter comparable oscillator. scale and the meter is in its normal operating environd. Adjust Distortion Analyzer SENSITIVITY Selectment and turned off, Adjust the zero-set, if necessary, or and VERNIER control for 0 DB reference. as follows: e. Switch FUNCTION selector to DISTORTION. Ada. Rotate mechancial zero-adjustment screw clockjust BALANCE controls and Frequency Dial for null wise until meter pointer is to the left of zero and movindication. ing upscale toward zero. f. Distortion shall be more than -40 db down. 5-22. ADJUSTMENT AND CALIBRATION b. Continue to rotate adjustment screw clockwise; stop when pointer is exa