HP-207A-Manual 电路图.pdf

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1、I . : HP Archive . . This vintage Hewlett Packard document was preserved and distributed by www. Please visit us on the web ! . . On-line curator: Tony Gerbic RadioFans.CN 收音机爱 好者资料库 207A AUDIO SWEEP OSCILLATOR OPERATING AND SERVICING MANUAL RadioFans.CN 收音机爱 好者资料库 O P E R A T I N G A N D S E R V I

2、C I N G I N S T R U C T I O N S F O R MODEL 207A AUDIO SWEEP OSCILLATOR Serial lland above Copyright 1957 by Hewlett-Packard Company The information contained in this booklet is intended far the operation and main- tenance of Hewlett-Packard equipment and is not to be used otherwise or reproduced wi

3、thout the writtenconsent of the Hewlett- Packard Company. HEWLETT -PACKARD COMPANY 275 PAGE MILL ROAD, P A L 0 ALTO, CALIFORNIA, U. S. A. i 207A002 RadioFans.CN 收音机爱 好者资料库 SPECIFICATIONS FREQUENCY RANGE: ACCURACY: DIAL: FREQUENCY RES PONSE : EXTERNAL FRE- QUENCY CONTROL: SWEEP TIME: TORQUE REQUIRED:

4、 OUTPUT: OUTPUT CONTROL: DE TORTION: HUM VOLTAGE: POWER: DIMENSIONS: WEIGHT: OPTION AVAILABLE: 20 cps to 20,000 cps, covered in one band. f470 including warm-up, changes due to aging components, tubes, etc. Six-inch diameter dial calibrated over 300 of afc. 21 db over entire frequency range. 1/4-inc

5、h shaft, extending from rear of instrument, rota- tion approximately 1500 for full frequency coverage. Recommended minimum time of sweep from one band edge to the other is approximately 20 seconds. Maximum torque required to drive rear shaft is approxi- mately 12 ounce-inches with the front panel ve

6、rnier re- move d. 10 volts into 600 ohms rated load, balanced o r 1 terminal at ground. Decreases level continuously by more than 40 db. Less than 1% over entire frequency range. Less than 0. 1% of rated output. Decreases as output is attenuated. 115/230 volts, +lO70, 75 watts. Cabinet Mount: 7-1/2

7、wide, 11-1/211 high, 14-1/4 deep. Rack Mount: 19 wide, 7 high, 12-1/211 deep. Cabinet Mount: 23 lbs. approximately, shipping 29 lbs. Rack Mount: 27 lbs. approximately, shipping 42 ibs. Modified to supply an output voltage (from an external dc voltage source) proportional to frequency for true logari

8、th- mic presentation. Specify: H01 207A (Cabinet Mount) H01 207AR (Rack Mount) CONTENTS SECTION I GENERAL DESCRIPTION Page 1-1 Introduction . . . . . . . . . . . . . . . . . . 1 - 1 1-2 Inspection. . 1 - 1 SECTION I1 OPERATING INSTRUCTIONS 2-1 Controls and Terminals . . . . . . . . . . . . I1 - 1 2-

9、2 Operating Procedure . I1 - 1 2-3 Output Circuit Options . I1 - 1 2-4 Addition of Sweep Voltage Potentiometer . I1 - 2 SECTION I11 CIRCUIT DESCRIPTION . 3-1 General. I11 - 1 3 -2 Frequency Controlling Bridge . . . . . . . . . . I11 - 1 I11 - 2 3-3 Balanced Push-pull Oscillator. 3-4 Output Circuit .

10、 I11 - 2 . SECTION IV MAINTENANCE 4-1 4-2 4-3 4-4 4-5 4-6 4-7 4-8 4 -9 4-10 4-1 1 4-12 4-13 4-14 General . IV - 1 Cover Removal . IV - 1 Tube Replacement . IV - 1 Replacement of Lamp R-16 . IV - 1 Replacement of Electrolytic Capacitors. . IV - 2 Replacement of Variable Resistors and Capacitors . IV

11、- 2 Replacement of Components in the two terminal Complex Network . IV - 2 Lubrication, Tuning -Capacitor Drive Mechanism. . I v - 3 Check for cause of Distortion . I v - 3 Calibration . IV - 3 Tracking Adjustments . IV - 4 Power Transformer Primary Connections . IV - 5 Trouble Shooting Chart . IV -

12、 5 Sweep Potentiometer Tracking Check. . . . . . . IV - 5 SECTION V TABLE OF REPLACEABLE PARTS 5-1 Table of Replaceable Parts . v - 1 Sect. I Page 1 SECTION I GENERAL DESCRIPTION 1-1 INTRODUCTION The Model 207A Audio Sweep Oscillator cov- ers the entire 20-cps to 20-kc frequency range ina single dia

13、l sweep. A synthesized RC net- work enables the oscillator to be tuned over a 1OOO:l frequency range without bandswitching, thus the entire audio range may be swept by a singla dial twist. This fpatur- makos th* 207A av-ry uspful test instrua1-nt inapplications in- volving response measurements of a

14、mplifiers, transformers, speakers, and many other au- dio devices. The dial calibration of the Model 207A is es- sentially logarithmic. This characteristic permits accurate presentation of waveforms on an oscilloscope or recorder when making response measurements. To facilitate such measurements, th

15、e 207A is arranged so that an extension of the tuning dial shaft is avail- able at the rear of the instrument. The shaft extension may be equipped with an accessory potentiometer which, when used with a suit- able d-c supply, provides alinear sweepvolt- age for use in observing response character- i

16、stics of audio devices. The shaft extension may also be equipped with a reversing-motor drive which permits automatic response meas- urements to be made. In addition to the above features the Model 207A retains all the basic advantages com- mon to the -hp- line of RC-oscillators, such as wave-form p

17、urity, constant output over a wide range, stability, calibration accuracy, and other important features shown in the TABLE OF SPECIFICATIONS. The Model 207A is ehsy to operate: frequency and amplitude of the output signal are set merely by operating dials on the control panel. The easily read, six-i

18、nch diameter frequency dial is calibrated over 300 of arc. Usefulness of the oscillator has been extended by designing the 207A output circuit so that it can be operated balanced as well as unbal- anced. The oscillator output provides a ma= imum of 20volts open circuit or 10 volts into a 600-ohm loa

19、d at any frequency between 20 cps and 20 kc. A bridged-T variable attenua- tor in the output circuit controls the output voltage level over a 40-db range. 1-2 INSPECTION This instrument was thoroughly tested and in- spected before being shipped, and is ready to use when received. After the instrumen

20、t is unpacked, it should be inspected carefully for any damage it may have received in transit. If any shipping damage is found, follow the procedure outlined in the Claim for Damage in Shipment section at the back of this instruction book. Sect. 11. Pagz 0 t E s 5 a d k bD d 0 d 4 P- O N I d I (3 S

21、ect. I1 Page 1 SECTION II OPERATING INSTRUCTIONS 2-1 CONTROLS AND TERMINALS On This toggle switch is in the power-supply in- put circuit, and in the ON position closes the line voltage to the power -supply transformer. With the transformer energized, an indicator lamp lights, and the glow visible th

22、rough the index window on the frequency dial indicates the instrument is turned on. FR EQ U ENCY DIAL This control varies the capacity in the fre- quency -determining network of the instrument and thus varies the outputfrequency. The dial is calibratcdfrom 20 cps to 20 kc over a 300 arc. The small k

23、nob (just below the frequency dial on cabinet models and to the right of the dial on rack modols) is a vernier control for the frequency dial. AMPLITUDE This control varies the setting of the bridged- T-attenuator in the output circuit. The cal- ibration narks are in arbitrary units, with maximum at

24、tenuation (and no output) at the zero setting, and minimum attenuation (and maximum output) at the maxi.nurri clockwise setting. 600, * (OUTPUT) The output voltage of the instrument appears at these terminals. The two terminals des- ignated 600- connect directly to the output of the AMPLITUDE contro

25、l and are used for a balanced output. The other terminal desig - nated with theModel 207A power cable plugged into a grounded female connector, the instrument chassis is connected to ground. ) NOTE If the Model 207A is being used to supply an unbalanced output, al- ways connect the left hand 600 ohm

26、 terminal to ground. Balanced Operation Connections for balanced operation are indi- cated in Figure 2-1. (The broken line from the ground terminal indicates the output cir - cuit is balanced to ground. ) The AMPLITUDE control in the output circ-uit is a bridged-T-attenuator and any setting ex- cept

27、 minimum attenuation unbalances the cir - cuit. Therefore for balanced operation the AMPLITUDE control must be set for maximum output (full cw). If smaller outputs are desired, withminimum noise turn the AMPLITUDE control maximum cw, and connect an external attenuator, de- signed for the frequencies

28、 involved, between the Model 207A and tne load. 2-4 ADDITION OF SWEEP VOLTAGE POTENTIOMETER A sweep voltage potentiometer is available, at extra cost, for factory installation on the Model 207A. Instruments with this modifi- cation are known as the Specification H01 207A/AR This potentiometer, when

29、attached to an ex- ternal DC voltage source, will produce a voltage proportional to the logarithm of the frequency generated by plus or minus 570. This voltage may be used to drive a recorder or may be attached to the horizontal input of an oscilloscope for direct display of the fre- quency characte

30、ristics of a unit under test. The potentiometer assembly is coupled to the frequency dial shaft which extends beyond the rear of the cabinet. Sect. I11 Page 1 SECTION 111 CIRCUIT DESCRIPTION 3-1 GENERAL The Model 207A Audio Sweep Oscillator is basically similar to other -hp- RC oscillators, however

31、the 207A sweeps the entire audio spectrum in a single frequency band: The manner in which the 207A accomplishes this broad single sweep is by means of a synthe- sized RC network in the frequency controlling bridge which controls the operating frequency over a 1OOO:l range. The 207Aoscillator include

32、s a frequency con- trolling bridge and a balanced push-pull amp- lifier circuit which constitute the oscillator, an output circuit which maybe arranged either for balanced or unbalanced operation, and apo wer supply circuit. These are shown in block-dia- gram form in Figure 3-1 and in detail in the

33、schematic diagram. 3-2 FREQUENCY CONTROLLING BRIDGE The frequency-controlling network inthe 207A is arranged as a floating bridge, symmetrical with respect to ground. With no connection to ground onany terminal of the bridge, stability of calibration is assured, since any stray cap- acity and leakag

34、e to ground present at the bridge output terminals do not shunt either the frequency or amplitude-controlling arms of the bridge. The frequency-controlling compo - nents comprise two arms of the bridge (Fig. 3-1) and consist of special two-terminal im- pedance elements (Z1 and Z2) and a variable con

35、denser C8. The network consisting of Z1 and 22 differs from the conventional RC net- work in that the resistance element of theRC pairs has been changed to an impedance ele- ment to effect a 1OOO:l frequency range in a single band. A comparison of the convention- al RC network with the 207A synthesi

36、zed RC network is described below in order to show how this 1OOO:l frequency range is effected. 1O:l Range Network In the conventional -hp- resistance-capacity oscillator the frequencyof oscillation is con- trolled by the combination of series and paral- lel RC networks as shown inbasic form in Fig-

37、 ure 3-2. The ratios of R1 to Rz and C1 to C2 are such that the frequency of oscillation is 1 expressedbyfo 1/2X RIC1.Norinallya 1O:l range-tuning capacitor-is used for C1 and C2, thus the oscillators cover a 1O:l frequency range in a single band. c Figure 3 -2 Basic arrangement of RC network used i

38、n -hp- oscillators. When the frequency characteristic of one of the RC pairs of the frequency-determining net- work is plotted on a reactance chart, the plot will appear as shown in Figure 3-3. At the I I I I I f 10 f l02f 103f F R E P U E N C Y Figure 3-3 Reactance plot of one RC pair in basic RC o

39、scillator. Sect. 1 1 1 Page 2 frequencywhere the resistance curve R inter- sects the reactance curve of the capacitor, the voltage eg out of the network (Figure 3-2) is in phase with the voltage ef applied to the net- work, and the overall circuit oscillates. As the capacitor is tuned through its 1O

40、:l range, the reactance moves through a 1O:l range (in- dicated by shaded area in Figure 3-3), con- sequently the frequency of oscillation moves through a 1O:l range. 1OOO:l Range Network The frequency-determining network of the 207A retains the same 1O:l range-tuning capacitor, but theresistance el

41、ement R is replaced with a synthesized impedance element which has a slope between 0 and -1, i.e., between that of a resistance and that of a capacitive reactance. By doing this, the limits of the frequency range over which the circuit canbe tuned occur where the impedance curve of the new network i

42、nter- sects the reactance limit lines of the tuning capacitor, as shown in Figure 3-4. Each of the two impedance elements used in the 207A has an impedance line whose slope approxi- mates -213 as shown in Figure 3-4, thus the frequency coverage of the oscillator has been expanded to cover a 1OOO:l r

43、ange in a single band. I I I I 1 f 103f F R E Q U E N C Y Figure 3-4 Reactance plot of impedance net- work The impedance elements approach a straight line characteristic of slope -2/3 by using a series of RC networks as shown inFigure 3-1. Each impedance element contains 6 resistors and 5 capacitors

44、 to achieve the required im- pedance characteristics. Figure 3-1 shows how the complete circuit appears when the two impedance elements are used. Amplitude Stabilizing Arms Avoltage divider which includes a thermally- sensitive resistance comprises the other two arms of the frequency-controllingbrid

45、ge. The amplitude is stabilized at such a level that the amplifier tubes are operated in the substan- tially linear portion of their characteristics. This results in a very pure sine wave oscil- lation. The bridge is fed by the balanced voltage de- veloped at the cathode of V3 and V4 in the out- put

46、 of the balanced amplifier. The output of the frequency-controlling branch of the bridge is applied to the control grid of V2 while the output of the amplitude-stabilizing branch is applied to the control grid of V1. 3-3 BALANCED PUSH-PULL OSCILLATOR The oscillator is a balanced push-pull circuit wh

47、ich includes an amplifier stage (Vl, V2) and a cathode-follower stage (V3, V4). The bal- anced output from the cathodes of V3 and V4 is fed back to the frequency controlling bridge and also to the primary of the output trans- former. Criss-cross positive feedback is used in the cathode-follower stag

48、e to provide an essentially zero output impedance as seen by the cathode-to-cathode load. Thus the OS- cillator can be operated into any finite load impedance with little reaction on the oscillator. The feedback paths are from the plate of V3 to the screen and control grid of V4, and from the plate of V4 to the screen and control grid of V3. The degree of positive feedback is a function of the load and increases as the load decreases, thus tending to maintain the out- put constant re