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Section 11Model 201CSECTION IIINSTALLATION2-1. INSPECTION.b. Connect a new jumper between terminal 3 and 4.2-2. Unpack the instrument upon receipt and inspect it forsigns of physical damage such as scratched panel surfaccs,broken knobs, etc. If there is any apparent damage, fde aclaim with the carrier and refer to the warranty page in thismanual.c. Change the line fuse to a 0.8 A slo-blo.2-3. An electrical inspection should be performcd as soonas possible after receipt. To aid in electrical inspection a listof performance checks are in Section V, Paragraph 5-8.These procedures make a good test as part of incomingqualitycontrol inspection.2-4. POWER REQUIREMENTS.2-8. The Model 201 C requires a power source of 118/230volts 10 76, 48 t o 440 Hz, which can deliver up to 120waits.2-6. POWER CABLE.2-1. For the protection of operating personnel, theNational Electrical Manufacturers’ Association (NEMA)recommends that the instrument panel and cabinet begrounded. This instrument is equipped with a three-prongconductor power cablc which, when plugged into anappropriate receptacle, grounds the instrument. The offsetpin on the power cable three-prong connector is the groundpin.2-8. To preserve the protection feature when operating theinstrument from a twocontact outlet, use a three-prong totwo-prong adapter and connect the pigtail on the adapter toground.2-9. 230-VOLT OPERATION.2-10. To operate the Model 201C from a 230-volt *IO%source, change the primary windings of T2 from a parallelto a series arrangement. Refer to the schematic diagram andproceed as follows:a. Remove the two bare wire jumpen from theterminals on T2. These jumpers connect terminal 2to 3 and 4 to 5 on the primary winding.2-11. REPACKAGING FOR SHIPMENT,2-12. The following is a general guide for repackaging forshipment. If you have any question, contact your local -hpSales andoffice.(seeAppendlx at the back ofthismanual for office location,)NOTEIf the instrument is to be shipped toHewlettPackard for service or repair,attach a tag to the instrument identifyingthe owner and indicating the service orrepair t o be accomplished; include themodel number and full serial number ofthe instrument. In any correspondence,identify the instrument by modelnumber, serial number and serial numberprefix.a. Place instrument in original container if available.If original container is not available, a suitable onccan be purchased from your nearest h p - Sales andService Office.If original container is not used,b. Wrap instrument in heavy paper or plastic beforeplacing in an inner container.c. Use plenty of packing material around all sides ofinstrument and protect panel faces with cardboardstrips.d. Place instrument and inner container in a heavycarton or wooden box and seal with strong tape ormetal bands.e. Mark shipping container withINSTRUMENT,” “FRAGILE etc.“DELICATE2-1

Section 111Model 201CSECTION 111OPERATING INSTRUCTIONS3-1. CONTROLS AND TERMINALS.3-2. ON. Toggle switch controls line voltage to instrument.3-3. RANGE. Three-position rotary switch selects variousvalues of resistance in the bridge circuit of the RCoscillator. The position of this switch indicates themultiplying factor for the frequency dial calibration.3 4 . FREQUENCY dial. This control varies the capacitancein the bridge circuit of the RC oscillator to vary outputfrequency between range switch steps. The dial is calibratedfrom 20 to 200 and its indication multiplied by the factorindicated by the RANGE switch will give the actual outputfrequency of the oscillator. The small knob below thefrequency dial is a vernier control for thc dial.3-5. ATTENUATION. This is a dual concentric control.The inner control is a potentiometer which adjusts theamplitude of the oscillator voltage admitted to theamplifier, and therefore, it adjusts the output voltage of theinstrument from zero to a maximum value established bythe attenuator. The outer control is a bridged-T typeattenuator providing 0 to 40 dB of attenuation in 10 dBsteps.3-6. OUTPUT terminal. Two binding posts on the lowercenter of the front panel are the output terminals for theoscillator. Terminal marked G is connected to the chassis ofthe instrument.3-7. OPERATING INSTRUCTIONS.a. Connect the power cable to required power source.b. Turn the power switch ON and allow approximatelyfive minutes for the instrument to reach its normaloperating temperature.c. Set the FREQUENCY dial and RANGE switch fordesired output frequency.d. Set ATTENUATION outer control to 0 dB, then setinner control (amplitude) for desired outputvoltage.e. Set ATTENUATION outer control, if desired, toreduce output level in 10 dB steps.NOTEWhen the attenuator is in the OdBposition the amplifier output is deliveredfrom less than 600 ohms at frequenciesbelow 5000Hz, and it will produce itsrated output (3 watts) across a load of600 ohms. When the attenuator ispositionedfor20 dB or moreattenuation, the internal impedance is600 ohms.3-8. LOW LEVEL APPLICATIONS.3-9. To avoid excessive noise and hum at low output levels( 4 0 dBm or less), it it good practice to attenuate theoscillator output -30 or 4 0 dB and use the amplitudecontrol as an output vernier to obtain desired level.3-1

Section IVModel IOSCILLATORVI 8. v2POWERSUPPLYAMPLIFIERv3, v4, v5t-0-40dbATTENUATOR600n 0 - l O d b600n 2 0 - 4 0 d bI-201CFigure 4-1. Block Diagram of Model 201C8 1988

Section IVModel 201CSECTION IVTHEORY O F OPERATION4-1. GENERAL.4-2. The Model 201C consists of an oscillator section, anamplifier section, an output attenuator and a power supplyas shown in the block diagam, Figure 4.1.BO044-3. OSCILLATOR SECTION.4 4 . The oscillator section consists of V1 and V2 as aresistance coupled amplifier containing two feedback loops.The positive feedback loop sets up oscillation while thenegative feedback loop reduces distortion and maintains aconstant amplitude of oscillation. The positive feedbacknetwork contains fixed resistances (established by theRANGE switch) and a variable capacitance. A simplifiedschematic diagam is shown in Figure 4-2. The network isdesignedsothat R l , C l A a n d B R 8 , C l C a n d D .IIITFREQUENCYFigure 4-3. Oscillator Network CharacteristicsIFigure 4-2. Simplified Schematic Diagram ofOscillator Section4-5. The oscillator output is coupled to the input stagethrough C8, and the input voltage is derived from thissignal. Oscillation will occur when there is zero phase shiftbetween the voltage applied to the network and the voltageapplied to the grid of V1. The zero phase shift point is alsothe point of minimum loss through the network as shownin Figure 4-3. The frequency of oscillation (relativefrequency in Figure 4-3) is given by the expression:1Fr 2 n d (R1 . ClA,B) (R8.ClC,D)-4-6. The cathode by-pass capacitors in the oscillatorsection C5, C7 correct phase shift at higher frequencies.4-7. The negative feedback network minimizes change ofoutput amplitude with change in frequency. Theincandescent lamp, used as a cathode bias resistor for V1, ispart of the negative feedback voltage divider. It has atemperature resistance characteristic such that its resistanceincreases in direct proportion to the voltage applied t o it.Thus, changes in its resistance will change the amount ofnegative feedback in the oscillator output. The thermalinertia of the lamp is great enough to be unaffected by sinewave voltages at the lowest frequencies involved.4-8.AMPLIFIER SECTION.4-9. The amplifier section of the instrument consists of avoltage amplifier V3A direct coupled to a phase inverterV3B, and a push-pull output stage V4 and VS. The outputtransformer contains a tertiary winding for overall negativefeedback around the amplifier. As a result of negativefeedback in excess of 30 dB, very little distortion isintroduced by the amplifier section of the instrument.4-1

Model 201CSection VTable 5-1. Recommended Test EquipmentModelRequired CharacteristicsInstrument TypeMulti-FunctionMeterDC Voltage Range: 1 to 310 voltsOhmmeter Range: 1 ohm to 500 megohmsAccuracy: 53%AC Voltage Ranee: 1 m v to 100 volts-hp- Model 421ADistortionAnalyzerDistortion MeasurementRange: 20 Hz to 20 kHz-hp- Model 33 1AFrequency CalibrationAccuracy : 2%Elimination Characteristics:Fundamental frequency reduced bymore than 60 dBSensitivity: Ability to measure distortionlevels of 1% full scaleIFrequency Range: 20 Hz to 20 llatorV6I- h p Model 5223LCHECK REQUIREDITable 5-5, step 26SNlGTVoltage Amp.phase inverterTable 5-5, step 36V6GT6V6GTOutput TubcOutput TubeTable 5-5, step 35AR4RectifierTable 5 - 5 , step 1I

Section VModel 201CSECTION VMAINTENANCE5-1. INTRODUCTION.5-10. CALIBRATION ACCURACY CHECK.a. Connect test setup as shown in Figure 5-15-2. This section provides maintenance and serviceinformation for the Model 201C Audio Oscillator. Thesection includes recommended test equipment, a tubereplacement table, performance checks, adjustments, repairprocedures and a troubleshooting table. The performancechecks will verify proper iiistrument operation.5-3. TEST EQUIPMENT.b. Check the period or frequency for each frequencysetting shown in Table 5-3.hpZOICAUDIOOSCILLATOR5 4 . Test equipment recommended for use in maintainingand checking performance of the Model 201C is listed inTable 5-1. Equipment having similar characteristics can besubstituted for the equipment listed.5-5. PERIODIC MAINTENANCE.5 4 . The tuning capacitor drive bearing should belubricated once or twice a year depending upon the amountof use. One drop of light machine oil in each of the bearingholes is adequate. The holes are located in the hearingprojections of the vertical casting behind the front panel.Figure 5-1. Calibration Accuracy CheckTable 5-3. Calibration Accuracy Check5-1. The inside of the instrument should be cleanedoccasionally to prevent accumulation of dust and dirt fromshorting plates of the main tuning capacitor.Clean tuning capacitor with extreme care.DO NOT apply any force to it whichcould beud the plates and destroycalibration. Compressed air under apressure not to exceed 60 psi isrecommended for cleaning.x120XI020020XI0020020sos

OPERATING AND SERVICE MANUAL -hp- Part No. 201 C-906 MODEL 201C AUDIO OSCILLATOR Serials Refixed: 0961 A Appendix C, Manual Backdating Changes. adapts this manual to Serials Prefixed: 35146357 and below, 331-, 311-, 308-, 236-, 133-, 006- and serials 1358 to 557 and below.