US2839960A - Electronic synchronizing system for producing pitch discs and the like - Google Patents

Description

June 24, 1958 E. M. JONES ELECTRONIC SYNCHRONIZING SYSTEM` FOR PRODUCING FITCH DISCS AND THE LIKE Filed DBG. 30. 1949 5 Sheets-Sheet 1 o l." Ix/ v e 0 u 0 MF. c

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E. M. JONES June 24, 1958 ELECTRONIC SYNCHRONIZING SYSTEM FOR PRODUCING PITCH DISCS AND THE LIKE Filed D60. 30, 1949 3 Sheets--Sheet 2 INVENTOR.

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/n WMM/lug ATTORN EYS niteti States Patent() ELECTRONIC SYNCHRNIZING SYSTEM FOR PRODUCNG PTCH DISCS AND THE LIKE Edward M. Jones, Cincinnati, Ohio, assignor to The Baldwin Piano Company, a corporation of Ohio My invention relates generally to the synchronization of a relatively low frequency electronic oscillator with a source of relatively high frequency oscillations so that the frequency of the former is a submultiple of the frequency of the latter. In particular, my invention relates to methods and means for causing one revolution or cycle of motion of a moving object, such as a turntable to occur during an integral number of cyclic variations in intensity of a light source.

The particular uses to which I have put my invention are: (1) producing pitch-determining scanning discs for photoelectric musical instruments, (2) producing voice (wave form) discs for such instruments, and (3) dividing a circle into any of a wide range of equal parts. It will be obvious to those skilled in the art that my invention has many other uses, such as producing scales for protractors, azimuth indicators and devices requiring the division of a given distance into equal parts or recurring patterns. Also, my invention may be used in electrical circuits in which a plurality of frequencies must be maintained in ratios of large prime numbers.

Although l shall describe my invention with respect to the three specific uses mentioned above, it will be understood that the appended claims shall be construed broadly to cover methods and means for producing equally divided re-entrant paths containing integral numbers of cyclic patterns and for graduating circles, scales and the like.

Certain aspects of my invention are specifically claimed in application Serial No. 436,831, led .Tune 15, 1954, entitled Electronic Synchronizing System for Producing Pitched Discs and the Like, which is a continuation-inpart of this application.

It is well known that musical tones can be produced by means of a system wherein, iirst, a beam of parallel light is directed through a series of playing-key-openable apertures selectively exposing small, circumferential segments of concentric rows of transparent areas in an opaque pitch disc rotated at a speed such that areas in respective rows pass their respective apertures at rates corresponding to the fundamental frequencies of the tones desired; second, the moving rays of light thus produced are caused to scan wave form patterns of a variable opacity or variable area type; and third, the varying rays are directed upon a photocell in an appropriate circuit including electroacoustic translating means. It is also known that to produce higher order harmonics of a given complex tone, the scanning rays must be extremely narrow, thus requiring that transparent areas in the pitch disc be narrow radial slots.

Extreme accuracy is required in locating the transparent slots equidistantly around the respective rows of a pitch disc. Random variations in the distance between adjacent slots are productive of extraneous frequencies resulting in low signal-to-noise ratios, while cumulative errors in spacing around a row of slots result in lowfrequency modulation, commonly known as wow.

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Also, those skilled in the art know that through a given aperture a plurality of cycles of wave-form patterns may be scanned simultaneously by an equal number of transparent slots and that the respective cycles of wave-form patterns must be spaced exactly the same as the transparent .slots which cause light beams to scan them.

As disclosed by Armand F. Knoblaugh in a copending application entitled Musical instruments Employing Continuously Moving Members, Serial No. 39,674, filed July 20, 1948, now U. S. Patent No. 2,586,664, granted February 19, 1952, practical pitch discs for photoelectric musical instruments may be of the order of one foot in diameter. Discs of this type require many rows of slots, some of which have prime numbers of slots of the order of 1000 and less for approximating the equally tempered scale. In making such a disc, a first criterion is an equal spacing of a given number of slots about the specific circumference of a given pitch track. The slots must be so spaced as to come out even, since otherwise there will be extraneous noise. A second criterion is accuracy in the spacing of the slots. My experience with such discs indicates that random variations in the distance between adjacent slots of the order of .0001 inch, obtainable by another method I have employed, produces a signal-to-noise ratio which is lower than desirable in high-quality electronic musical instruments.

Previously employed methods of producing pitch discs have either lacked the accuracy desired or have required large amounts of time for their production. In the practice of one phase of my invention I rotate a transparent disc or other element having a photosensitive coating thereon by means of a synchronous motor energized from a source the frequency of which can be altered from a nominal one as required to make one revolution correspond exactly in time to that of an integral number of pulses of energy supplied to a light source which is used to produce the images of the slots upon the photosensi.- tive coating for exposure thereof.

My invention, in brief, comprises a system by means of which a wide range of dividing ratios between the frequency of the light pulses, or variations and the speed of the motor, is available so that the desired number of photographically produced slots or cycles of wave forms may be produced in the respective concentric rows. During the exposure of a given row, a disc may be rotated a number of times in order that the individual cyclic areas may receive suticient light to expose the photographic emulsion. It can readily be seen that these requirements necessitate an extremely stable and precise system. The speed of the motor must be extremely constant and the dividing ratio between the frequency of light variations and the frequency of the energy supplied to the synchronous motor must be an exact integer.

A broad object of my invention is to provide methods and means for dividing re-entrant paths into integral numbers of cyclic patterns.

A still further object of my invention is to produce a voice disc for a photoelectric musical instrument.

An object of my invention is to provide means for synchronizing the frequency of the output of a variablefrequency harmonic synthesizer and the speed of a synchronous motor so as to produce an integral number of cycles of a desired wave form during each revolution of a member driven by the motor.

Another object is to provide a harmonic synthesizer which will supply a complex wave, the harmonics of which are variable as to amplitude and phase with respect to the fundamental and the frequency of which can be varied as desired without appreciable change in harmonic content.

These and other objects of the invention, which will be set forth hereinafter or will be apparent to one skilled in the art upon reading these specifications, I accomplish by those certain constructions, circuits and arrangements of parts of which I shall now describe exemplary embodiments.

Reference is made to the accompanying drawings wherein:

Figure 1 shows a block diagram of a basic system .for obtaining one revolution of a turntable during an in-Y tegral number of pulses of light.

Figure 2 is a block diagram of a portion of the system of Figure 1, such as I employ for synchronizing the speed of a turntable with cyclic variations of light other than pulses.

Figure 3 is a block diagram of the same portion of the system of Figure 1, such as I employ for synchronizing the speed of Va turntable with pulses of light.

Figure 4 is a block diagram of the essential elements in a synchronizing system according to my invention.

Figure 5 is a graphical representation of the wave form of voltage across'the tuned circuit of the low-frequency oscillator of Figure 4.

Figure 6 illustrates the wave form of the output of the direct-coupled amplifier of Figure 4.

Figure 7 is a diagram, partly schematic, partly block, of a complete system for graduating a circular path.

Figure 8 shows a graph of the relationship between the reading of a peak voltmeter and the frequency of a high frequency source.

Figure 9 illustrates an aperture system such as may be employed with my invention.

Figure 10 shows a portion of a pitch disc having a coradial series of slots.

Figure ll represents part of a series of graduations such as may be produced by the system of Figure 7.

Figure 12 represents a series of indexed graduations.

Figure 13 shows exaggerated results of a method by which the graduations of Figure 12 may be produced.

Figure 14 shows a plurality of wave form patterns such as may be produced by the system of Figure 15.

Figure '15 is aediagrammatic representation of a harmonic synthesizer and a synchronizing circuit therefor.

Figure 16 illustrates a synchronous motor and turntable assembly.

The basic problem The basic problem to which the hereindescribed exemplary embodiments afford a practical solution, is to cause one revolution or cycle of motion of an element to occur in exactlythe same amount of time required for a preselected number of electric pulses or of cycles of a cyclic electric wave of desired form generated by a separate source. Ancillary to the basic problem is the problem of causing a light source to vary in intensity in accordance with the pulses or with the variations in amplitude of theelectric wave.

General method The solution to the basic problem lies, according to my invention, in the following general method. First, I produce relatively low-frequency oscillations at a rate which determines the rotational speed of a synchronous motor driving the moving element. Second, I generate relatively high-frequency oscillations which can be varied over a range of frequencies depending upon certain requirements to be discussed in detail hereinafter. Third, by a series of dividers, I divide the high frequency oscillations by consecutive integral powers of the dividing ratio of the dividers. Fourth, I select from the series of dividers a particular divider having a frequency range over the range of adjustment of the high frequency generator) in which there occurs that particular frequency which vwill produce the desired number of cycles during one revolution of the element driven by the synchronous motor. Fifth, I synchronize the frequency of the lower 4 frequency oscillations with that of the higher frequency oscillations so that the former is exactly a submultiple of the latter. Sixth, I modulate the intensity of a light source at the rate selected in step four of this method.

If the modulation of the light source is to be in the natureof a pulse, I generate a pulse of a desired shape at the frequency selected in step four above.

If the modulation of the light source is to be in the nature of a sine wave, or of complex variations, I first generate oscillations of the desired wave form and then synchronize their fundamental frequency with the frequency of the pulses generated at a rate selected in step four above.

The basic system Briey, in the practice of my invention, I employ a relatively yhigh-frequency, variable-frequency oscillator 1 (Figure l) which is continuously variable over a range of at least two-to-one. A second oscillator 2 is tixedtuned at a relatively low-frequency which can be altered slightly by the injection of a synchronizing pulse from the synchronizing circuit 3 into its tuned circuit during each cycle of oscillation. By proper injection of this pulse, it is possible to make the frequency of the L. F. oscillator 2 a submultiple of the frequency of the H. F. oscillator 1, no matter what the frequency of the latter may be within its range.

My invention in one of its broader aspects concerns itself with what I believe is a novel system for introducing the synchronizing pulses just referred to. However, in the specific uses which I make of the system I may employ additional circuits in connection with the oscillators described above.

First, I may use the H. F. oscillator 1 to trigger a series of frequency dividers collectively designated at 4, each dividing by two the frequency of the preceding one. Second, a pulse generator 5, connectable by a selector switch 6 to one of the dividers 4 for a desired dividing ratio, is triggered by that divider and determines the frequency at which a light modulator 7 modulates the intensity of a light source 8, such as a crater lamp. Third, the L. F. oscillator 2 may be used to determine the frequency of a wide-pulse .generator 9 which supplies,

through a power amplifier 10, pulsating direct current to a synchronous driving means, such as a motor 11 driv-V ing a turntable 12, upon which may be mounted a photosensitive plate to be converted to a pitch disc or voice disc, or upon which a divided circle is to be formed.

The general system of Figure l, just described, provides means whereby one revolution of a turntable will occur during a desired whole number of cyclic variations in the intensity of the light source.

When I desire to produce during each revolution of the turntable 12 an integral number of cycles of a specific wave form, the light modulator 7 of Figure l comprises those elements of Figure 2 included in the area bound by the dashed line 7a-namely, a variable-frequency, variable wave-form, harmonic synthesizer 13, the fundamental frequency of the wave desired therefrom being synchronized by means of a synchronizing circuit, indicated generally at 14, with the pulses provided by the pulse generator 5 via the point 15a, which in this case is connected to the pulse generator 5 at the point 1S. The synthesizer may include amplification means for supplying to the lamp 8 sulicient energy to produce a desired level of intensity.

If I desire to produce during each revolution of the turntable 12 an integral number of pulses of light I simply employ in the place of the light modulator 7 a power amplifier 16 (see Figure 3), the terminal 15b being connected to the pulse generator 5 at the point 15.

The oscillator synchronizing system The synchronizing circuit -3 ofFigure preferably comprises the general circuit divisions shown in Figure 4 in the area surrounded by the dot-dash line 3a, although in the broader aspects of my invention I am not limited thereto. It will be obvious as these specifications are read that other synchronizing circuits could be employed.

Referring to Figure 4, the relatively high frequency oscillator 1a may be continuously variable, if so desired, over a range of frequencies determined by the dividing ratio of dividers such as 4 (Figure l), as will be explained in detail hereinafter. The relatively low frequency oscillator 2a, preferably of the L-C type, is fixed-tuned at a frequency fn suitable for a desired purpose, such as determining the speed of a synchronous motor. The frequency of this oscillator 2a can be altered slightly by the injection of a synchronizing pulse into its tuned circuit during every cycle of its sine-wave oscillation. When this is done, the wave form 20 of the voltage across this tuned circuit will have a notch in it as indicated at 21 in Figure 5, effectively altering it to a different frequency. By the proper introduction of the synchronizing pulse, it is possible to make the L. F. oscillator 2a operate at a frequency which is a submultiple of the frequency of the H. F. oscillator 1a. Since the frequency imposed on the light source 8 from the selected divider is also a submultiple of the frequency of the H F. oscillator, it will be evident that the frequency of the light source and the altered frequency of the L. F. oscillator 2a will be related as a whole-number ratio.

The method of injecting the synchronizing pulse will be explained in general first, the circuit details being described` hereinafter. The sine-wave voltage from the L. F. oscillator is fed through a direct-coupled amplier 22 (Figure 4), the output of which would normally be substantially a square wave, due to overloading, as indicated by the dashed curve 23 in Figure 6. The actual output of the amplifier 22, as-represented by the solid line 24, is a pulse, because of the feedback of a blocking oscillator 25 (Figure 4) discussed in detail hereinafter.

Trigger pulses from the H. F. oscillator 1a are fed to the blocking oscillator 25 along with the output of the direct-coupled amplifier 22 via an amplifier-and-mixer 26. The bias on the blocking oscillator 25 is adjusted so that it will not be triggered by a pulse from the H. F. oscillator la until the pulse 24 from the direct-coupled amplifier 22 has started. Since the beginning of the pulse 24 occurs at a certain instant in each cycle of the L. F. oscillator 2a., the blocking oscillator 25 will fire on the first trigger pulse from the H. F. oscillator 1a after the instantaneous voltage of the L. F. oscillator 2a passes through a certain value (in a positive direction).

Thus the period of the blocking oscillator 25 is always about l/fn and an exact multiple of the period of the H. F. oscillator (where fn, as mentioned above, is the resonant frequency of the tuned circuit of the L. F. oscillator 2a). However, the former period would alternate between two adjacent values if means were not provided to regulate it automatically.

The period of the L. F. oscillator 2a is altered during each cycle by combining the output of the direct-coupled amplifier 22 with a pulse from the blocking oscillator 25 and feeding it through a diode 27 to the tank circuit of the L. F. oscillator 2a. The blocking oscillator pulse puts a small negative charge into the condenser in the tuned circuit of the L. F. oscillator 2a forming the notch 21 in the curve 20 and delaying the progress of the wave slightly, so that its frequency is equal to that indicated by the dashed sine wave 20a, representing a frequency which is a submultiple of the frequency of the H. F. oscillator 1a. The size of the notch 21 depends upon the instantaneous value of the voltage from the direct-coupled amplifier 22. If, for a desired ratio between the frequencies of the high and low frequency oscillators, the trigger from the H. F. oscillator is slow in coming, the pulse from the direct-coupled amplifier 22 is given a chance to build up to a more negative value so that when the blocking oscillator pulse does occur, a larger ratio of frequencies is obtained. As the frequency of the H. F.y oscillator 1a is lowered, there occur sudden rises in frequency of the L. F. oscillator 2a as the blocking oscillator 25 suddenly shifts to firing on an earlier trigger, and the size of the notch 2l in the curve 20 suddenly shifts from a maximum to a minimum value.`

If the frequency of the H. F. oscillator 1a is varied, transitions from one ratio to another occur as the frequency of the H. F. oscillator is tuned throughout its range.

Circuit details of the oscillator synchronizing system The circuit details of the oscillator synchronizing means are presented in Figure 7, which shows a complete system for graduating a circular path. (Portions of the system which correspond to those previously described, have the same number but a different suffix letter; for example, the block 3 in Figure l represents the synchronizing system, whereas in Figure 4, the synchronizing system comprises elements enclosed by the dot-dash line 3a.) l shall first describe the circuit, thereafter explaining its operation in detail with reference to making a pitch disc or dividing a circle.

ln Figure 7 a variable H. F. oscillator 1b, preferably of the electron-coupled type, known in the art, is provided with a tuning dial 30 for changing the frequency thereof. The pulsed output of the oscillator 1b is connected as shown to a series of frequency dividers 4a, 4b, 4c, etc., preferably multivibrators of the hip-flop type, each dividing by two the frequency of the pulses fed to it. Either the oscillator 1b or a divider such as 4a may be used as a source of variable frequency oscillations and may be connected as at 31 and 33 to a selector switch 32, for selecting a desired range of dividing ratios.

The dividers 4b, 4c, and 4a are respectively connected to terminals 34, 35 and 36 of a selector switch indicated generally at 6a. The common terminal 37 of the switch 6a is connected to a pulse generator 5a, which in turn is connected to a power amplifier 16a. The output of the power amplifier is connected to the electrodes of a light source 8c, such as a crater lamp. A light 'beam from the crater lamp is directed toward an aperture system comprising an opaque member 38 having a transparent slot 39, through which a ray passes and isconverged by a condensing lens 40 toward a second lens 41. A minute image of the slot 39 is produced by the second lens 14 upon the surface of the disc 42, which may be coated with a photosensitive emulsion and may be located on a turntable 12a driven by a synchronous motor 50, described below.

I may, for reasons hereinafter given, employ an additional frequency divider 43 connected as shown by means of a selector switch 44 to the other dividers such as 4b, 4c and 4d. The divider 43 may be connected through a switch 45 to another pulse generator 46, the output of which may be fed to an amplifier 47, thence to a second crater lamp 48. By means of a mirror 49 the beam from the lamp 48 may be diverted and directed through the aperture 39 and lens system to the plate 42.

The `contact arm of the switch 32 is connected as shown to an amplifier and mixer circuit 26a, the output of which is connected to the grid of a vacuum triode T1, which acts as a cathode follower. Tubes T1 and T2, together withtheir associated components, comprise the blocking oscillator group 25a. The cathode of tube T1 is grounded through the resistor R1 and is connected through the winding L3 of a transformer indicated generally at 51 to the grid of the blocking oscillator tube T2. The plate of tube T2 is connected through the winding L1 of the transformer 51 to a positive plate potential V3 at the point 52. The cathode of tube T2 is connected through a resistor R2, paralleled by a capacitor C1, to a positive bias potential V1, lower than the potential V3. The winding L2 of the transformer may be connected as shown to a trigger amplifier 54, the output of which is connected to a wide-pulse generatorSS, which in turn is connected to the power amplifier S6. The winding of the synchronous motor 50 is energized from the power amplifier 56. Although the preferred type of motor employed by me in the practice of my invention will be discussed in detail hereinafter, it should be stated at this point that I use a direct drive as one of several features to obtain as nearly constant speed as possible. Consequently, by way of example, if I desire to run the turntable 12a at a speed of the order of 2 R. P. S. by means of wide pulses at a frequency of the y/order of 256 C. P. S., I will need 128 teeth on the rotor and a matching set of 128 teeth on the stator.

The cathode of the tube T2 is also connected to the cathode of a vacuum triode T3 which, together with Y indicated generally at 2b, and comprising vacuum triodes Y T5 and T6 and associated components. The plate of the tube T3 is connected to the grid of a cathode follower triode T4. Positive plate potential V3 for the tubes T3 and T4 may be connected at the point 58, the resistor R4 being in series with the plate of the tube T3. The cathode of the tube T4 is connected to ground through a resistor R5 paralleled by capacitor C2. The output of the cathode follower is carried to a common point 59, from which a connection is made to the amplifier and mixer circuit 26a through a resistor R6 and capacitor C3. The potential at the point 59 is measured by a peak voltmeter 60. Point 59 is connected also through a capacitor C8 to the cathode of a vacuum diode T7, which is biased through a resistor R14 at a positive potential V2 of an amount between V1 and V3 above. The plate of T7 is connected through the lower section 61 of a double-pole, double throw switch 62 and through the winding L4 of the transformer 51 to a resonant circuit comprising a capacitor C4 and an inductive element L5 in the L. F. oscillator 2b. The other section 63 of the switch 62 provides means for connecting the resonant circuit L5-C4 to ground through a variable capacitor C7. The other side of the circuit L5-C4 is connected along with the cathode of the oscillator tube T5 to the potential V1 at the point 65. The coil L6, which is inductively coupled to L5, is connected in series with the resistor R13 between the plate of tube T5 and the positive potential V3.

The grid of tube T5 is connected as shown in Figure 7 through a network consisting of capacitor C6, and resistors R9, R10 and R11 to the cathode of tube T6, acting as a cathode follower, the grid of which is connected to the tuned circuit LS-C4. The grid of the direct-coupled amplifier tube T3 is connected to the grid of tube T5 through resistor R8 and capacitor C5 as shown. The grid of tube T3 is connected also to ground through resistor R3 and to the plate of tube T5 through resistor R7.

The cathode of the tube T6 is connected also through aphase-shift network 70 to one of the horizontal and to one of the vertical deection plates of a cathoderay tube T8. Also connected to the same vertical deection plate are capacitor C10, which transmits a pulse from the pulse generator 5a, and capacitor C11, which transmits a pulse from the blocking oscillator 25a. The other horizontal and vertical plates, along with the second anode of the tube T8, are connected to the relatively 8 high potential V4. A focus potential is supplied inthe usual manner at 71. A potential between the grid ,and cathode of the tube T8 for varying the intensity of the trace is provided by the potentiometer R12 in series with the source of potential V1. A series resistor R18 is connected between the variable contact of the potentiometer and the grid of the tube T8, this grid being connected also to the plate of a vacuum triode T9. The grid of tube T9 is connected through a capacitor C9 toV the fixed set of plates of a variable capacitor C12, the movable plates of which are mounted upon the turntable 12a, which is electrically grounded. Connection to the positive potential V4 for the capacitor C12 is made through a resistor R17, as shown. The cathode and grid of tube T9 are respectively connected through resistors R15 and R16 to ground as illustrated in Figure 7.

An exemplary set'of values for the elements in Figure 7 is listed below:

R1 ohms 27,000 R2 do 18,000 R3 megohm 1 R4 do 1 R5 ohms 30,000 R6 do 100,000 R7 megohms 1.8 R8 ohms 82,000 R9 do 3,400 R10 do 27,000 R11 do 27,000 R12 do 650,000 R13 do 66,000 R14 do 47,000 R15 do 10,000 R16 megohms 2.2 R17 do 4.7 R18 ohms 130,000 C1 rnf .01

C2 mmf 800 C3 rnmf 300 C4 mmf-- 12,500 C5 mmf 1,500 C6 mmf 2,200 C7 mmf 140 (max.) C8 mf .01 C9 mf .0034 C10 mmf 25 C11 mmf 25 C12 mmf 15 (max.) L1 turns-- 167 L2 do 42 L3 do 83 L4 do 84 L6 henn'es 8 L6 do .2

T1 6SN7 (1/2) T2 6SN7 (1/2) T3 6SL7 (1/2) T4 6SN7 (1/2) T5 6SN7 (1/2) T6 6SN7 (l/2) T7 6H6 (1/2) T8 902A V1 volts 95 V2 do 165 V3 do 275 V4 do 420 Crater lamp-R1130B (Sylvania) No. of teeth in synchronous motor- 1284 Nominal frequency of L. F. oscillator 2li-500 C. P. S.

Frequency range of H. F. oscillator 1b-256 to 512 kilocycles sec.

Nominal frequency of pulses fed to motor-250 C. P. S. (employing as the pulse generator 55 a multivibrator circuit, dividing by two its input frequency) '9 Width of pulses fed to motor- 1700 microseconds Nominal speed of synchronous motor 50-2 R. P. S.

(approx.) (more accurate]v ?.50/ 128) I shall next explain the operation of the system shown in Figure 7. The sinusoidal potential developed across the tuned circuitl L-C4 is applied to the grid of the cathode follower tube T6 resulting in a sinusoidal potential at the cathode of tube T6. The potential on the grid of the tube T5 would be a sine wave except that the positive half is flattened due both to grid current flow and to the fact that R16 is large enough to prevent excessive grid current. Feedback potential for sustaining the oscillations in the tuned circuit L5-C4 is obtained from the plate circuit of tube T5 by inductive coupling between the windings L6 and L5.

A signal is fed from the L. F. oscillator through the resistor R8 and capacitor CS to the grid of the tube T3 in the direct-coupled amplifier 22a, the purpose of which is to provide a steep-front wave occurring at the instant that the sine-wave oscillation in tuned circuit L5--C4 passes through the zero point in a cycle. Resistors R9 and R11 act as a voltage divider for the purpose of fixing the D. C. bias Aon the grid of tube T3 at a point which permits tube T3 to start conducting at the exact half-cycle point in a given sine-wave of oscillation of the circuit L5-C4. This prevents the L. F. oscillator from oscillating at different amplitudes due to changes in amplitude of the synchronizing pulses which will be discussed below. After the plate potential of the tube T3 has gone to quite a low value it is desirable to terminate the pulse and somehow bring the wave back positive again. This is accomplished by two means. First, since the cathode of the amplifier tube T3 is connected directly to the cathode of the blocking oscillator tube T2, the instant that oscillation starts therein, a positive voltage occurs on the cathode of tube T2 and also on the cathode of tube T3, thus cutting the tube T3 off. However, this positive voltage on the cathode of the T 2 tube does not last very long and additional means for keeping the direct-coupled amplifier tube T3 cut 'off s employed. This second means is the resistor R7 which feeds to the grid of the tube T3 from the plate of the oscillator tube T5 a potential which accomplishes the desired result of keeping Vthe tube T3 cut off after the blocking oscillator pulse has subsided. The output of thev tube T3 is fed to the cathode follower tube T4. The

wave form hence is a negative pulse, terminated on its decay side as explained above. The output of the cathode follower tube T4 is fed through resistor R6 and capacitor C3 to one of the input points of the amplifier and mixer 26a,-the output of which triggers off the blocking oscillator tube T2 through the cathode follower tube T1. However, the trigger is not effective until the amplifier and mixer 26a also receives a trigger from the oscillator 1b, or from a divider such as 4a, via the selector switch 32. Hence, the blocking oscillator tube T2 will fire after the pulse on the cathodefollower tube T4 has started occurring, but not until a trigger pulse is received via the selector switch 32.

When theblocking oscillator fires, a voltage is induced across the winding L4 and conduction occurs in the diode T7, causing the notch mentioned above to occur in the sine wave across the oscillator winding L5.

The size of the notch depends upon what the magnitude`v of the negative pulse on the cathode of the tube T4 is at the instant the blocking oscillator-fires, If the 'trigger from the high frequency oscillator is late, the notch is greater due to the fact that the end of the winding L4 marked is at a more negative potential. Because the notch is greater, the progress of the sine wave is delayed more so that the next trigger will not occur any later with respect to the sine wave.

A quantity depending upon the size of the notch in the sine wave is measured by the peak voltmeter 60.

.1() The peak voltmeter measures the negative peak of the voltage on the' cathode follower tube T4. The reason why the negative peak is significant is that it shows how late the trigger is working, because as soon as the trigger occurs, the build-up of the negative pulse on the cathode follower is terminated.

The sine-wave oscillation occurring across the coil L5 is caused to produce a circular pattern on the scope T8 by means of a phase-shift network 70 which feeds voltages degrees out of phase to the deflection plates. A series of vertical markers, such as pips, is superimposed upon the circular pattern by pulses from the pulse generator 5a through a capacitor C10, the switch 37 being setto a standard position and the dial 30 being adjusted so that a recognizable scope pattern is obtained. The recognizable scope patterns will occur when ever the frequency of the pulses produced by pulse generator 5a is an integral-multiple of the frequency of the L. F. oscillator 2b.- When the desired dividing ratio differs from one of these ratios, the H. F. oscillator is first adjusted to give the nearest dividing ratio which has a recongnizable scope pattern; then the dial 30 of the H. F. oscillator is slowly turned in the proper direction until the peak voltmeter 60 has indicated a number of transitions equal the difference between the desired ratio and the above-mentioned nearest ratio producing the recognizable Scope pattern. For example, if the ratio between the frequency of the H. F. oscillator 1b and the frequency of the L. F. oscillator 2b is to be 899 and the nearest ratio producing a recognizable pattern is 896, then the dial 30 is adjusted until the recognizable pattern is obtained (it might comprise, for example 14 pips superimposed up the circular pattern). The dial is then turned in the increasingfrequency direction until three transitions are made as observed on the peak-voltmeter 66. Referring to Figure 8, the saw-tooth characteristic shows an exemplary relationship between the reading of the peak voltmeter 60 and the setting of the dial 30. If the dial is set betweenfl and f2 the dividing ratio will be 896. As the dial is turned in the higher frequency direction, three transitions from the maximum to the minimum peak voltmeter reading will occur before the desired ratio of 899 is obtained. This ratio will be maintained so long as the dial is set between f3 and f5. When it is desired to keep such aratio fora considerable time, the dial should be set at f4, halfway between f3 and f5, which corresponds to the peak voltmeter reading e2, halfway between the extremes el and e3, so that any drift due to variations in temperature, line voltage, etc. will not allow the system to shift to an adjacent dividing ratio.

j It will be clear that one highly advantageous feature of my invention is that minor shifts in the frequency of the H. F. source will not affect the dividing ratio. For example, if the H. F. oscillator frequency shifts to a slightly lower value, such as between f3 and f4, the peak voltmeter reading will increase, indicating, as explained above, that a larger delaying charge is being introduced into the L. F. oscillator, reducing its frequency until it is exactly 1/899 of the frequency of the H. F. oscillator. Also, without losing synchronism, it is possible to readjust'the high frequency oscillator to bring the peak voltmeter reading back to the mean value e2 before a shift to an adjacentdividing ratio occurs.

I shall now describe the manner in which the system of Figure 7 can be employed to produce two or more concentric series of areas on a disc 42, an area in one series being' coradialwith one area in the other series. First, l synchronize the system so that I may expose a desired number of areas in the first of the two series. Next, I throw the switch 62 to the upper position, so that no synchronizing pulses are introduced into the tuned circuit L5-C4 of the L. F. oscillator 2b. Then I adjust the condenser C7 until the frequency of the L. F. oscillator'7b is almost in synchronism with the H. F. oscillator 1b. This is evidenced by the slow movement of the pat- 1 tern on the scope T8V produced by the pulses from pulse generator 5d. During each revolution of the turntable 12a.`the plates of -the capacitor C12 will mesh and cause a cut-oit of the plate current in the tube T9, which has been conducting (due to the potential dropin the 'righthand portion of potentiometer R12), thuscausing the grid of tube T8 to be at a potential lower than that at the movable terminal of potentiometer R12. Thus the cut-Oifof plate current iu tube T9 will result in an increase i'n the intensity of the scope T8 once in each revolution of the turntable 12a, during the time that the condenser plates are enmeshed. The plates must be o'f such size that the angular displacement of the disc which occurs during the meshing of the plates is less than the disc displacement from one set of motor teeth to the next. Thus, since the rotor o'f the synchronous motor is allowed to drift (-by not being in synchronism), eventually one of the-many moving pips caused by pulses from the generator 5a will be superimposed upon the one xed pip (the circular trace and this pip are derived from theV same L. F. source) on the scope caused by the pulse from the winding L2 of the blocking oscillator 25a during the intensified period when the plates of capacitorY C12 are enmeshed. At this instant the switch 62 is thrown to the synchronizing (lower) position and pulses from the generator 5a Will remain superimposed upon the pulse from the blocking oscillator occurring on the intensified trace. After an exposure has been made for producing 'the iirst series of areas, the aperture 39 or the whole optical system is shifted to the position corresponding to the radius desired for the second series of areas.

A structure, such as that illustrated in Figure 9, may be used conveniently for shifting the aperture. The slider 3821 has an aperture V39a of desired dimensions, and is movable with respect to the member 3817' which has a longer aperture 39h.

If a different number of areas is desired in the second Y series, the new dividing ratio is selected and the system is made to occur at this instant, it will produce an vil'nag'e'on a particular radial line which will always be Vthe'saine for the various rows of areas exposed. Thus it is possible to establish coradiality between two areas or graduations in diierent concentric series. An example of coradial relationship is illustrated in Figure l0, wherein a portion 66 of an opaque pitch disc for a photoelectric musical instrument has coradial transparent slots 67, 67a and 67b in three adjacent concentric rows. `1 Y The above description referring to Figures 7 and'9 has been concerned with the production of one or more circular series of equal length graduations on a disc.V In Figure ll is shown a series of such graduations 72; I`n order to meet certain of the objects of my invention, 'I provide means for causing'certain regularly-spaced"grad-v uations to be longer than the others for indexing purposes. An example of such a series is illustrated in Figure 12. Graduations such as 73 are longer thanrthose designated as, but not as long as those numbered 74. I can index graduations by either of the following systems.

First, I may produce the extended portions of the longer graduations by exposing these areas simultaneously with the areas of which they are an extension. InvFigure 13 is illustrated a series of graduations produced by this method. However, the spaces between the extended porg: tions 73a and the main portions 72a has been exaggerated for the purpose of illustrating the technique involved. The means employed to accomplish this, result comprises the `elements at lthe right-hand end of Figure 7. If the selector switch 44 is connected to the same divider as" the switch 6a, and if the switch 45 is closed, the pulses of light which will be emitted from the crater lamp 48 will not occur as often as the pulses produced by the lamp 8c.

For example, if the frequency divider 43 is a systemV which will divide by 5, then the extended portions 73a of the graduations in Figure 13 will appear on every 5th one of the graduations produced by the exposure of the plate 42 by the lamp 8c. It will be obvious that an additional means similar to that comprising the elements between the selector switch 44 and the mirror 49, but con-` nected to a Vdifferent divider, can be employed to produce additional prolongations 74a of the graduations already obtained by the system just described.

As'another procedure, I may index a series of graduationsrby exposing first the normal areas 72; shifting the aperture 39!) of Figure 9 to a position corresponding to that of the extended portion 73a of a graduation 72a; third, selecting a different dividing ratio; and fourth, exposing a new series of areas to obtain prolongations 73a of graduations 72a. described system for obtaining exposures which are coradial will have to be employed in order that the ex'- V tended portions 73a are properly aligned with the graduaspond to a pulse frequency with which the cycles 72C,

72d, etc. of a desired wave form are synchronized.

y Harmonic synthesizer In the synthesizer, I use a method of the pulse-sampling type. Although systems employing this general method are described in an article entitled Method for changing frequency of a complex wave in the Proceedings of the National Electronics Conference, Chicago, Illinois, 1946, l prefe r to use a diode system together with means for controlling of amplitude and phase of the harmonics with respect to vthe .fundamental frequency, which I believeis..

novel., inorderV that I can meet objects of my invention pertaining to the provision during one revolution of a disc, or the like, ofV an integral number of cycles of various wave forms. Y

.The harmonic synthesizer, represented by the block 13.0f Figure 2, is shownin greater detail in the area surrounded by the dot-dash line 13a of Figure l5.. The

synchronizing circuit, enclosed in the area 14a will be described in detail below in another section.

In Figure l5, a crystal oscilaltor 75, generating a relatively high frequency signal'of the order of lOll kilocycles per second, is connected toa pulse generator or a blocking oscillator 76 for control of the oscillation frequency thereof at a frequency equal to or a submultiple of the crystal oscillator. The harmonically-rich oscillations from the blockingv oscillator 76 are fed to a series of parallel filters, twoof which are illustrated generally atr77 and 77a. i

The blocking oscillator output enters each filter through a series resistor, such as 85, a, connected in series to ground with a potentiometer 82, 82a, etc. The complex potential, is fed therefrom to one tuned circuit 78, 78a,

in each filter through a resistor 79, 79a and to another The Y tuned circuit 80, Silla through a capacitor 81, 81a. two tuned circuits 7 8 and 80 of iilter 77 are tuned to the fundamental frequency of the blocking oscillator output; 'tlie Vtuned circuits 78a and 80a of the iilter 77a are tuned to the second harmonic of the blocking oscillator outpii'tgand so on. The axes of theiiidubtive 'elements of 'the tuned circuits 78 and 80 are' 90 degrees apart and It will be obvious that the above-V their respective voltages are 90 degrees apart, so that when apick-up element 87 is rotated, the phase of the induced E. M. F. is shifted uth respect to the blocking oscillator output, hence with respect to other harmonics derived from other filters, such as 77a. The amplitude of the E. M. F. in pick-up element 87 can be controlled by the potentiometer 82. The purpose of the resistor 85 is to provide means for adjusting the maximum amplitude of the E. M. F. derived from the pick-up element 87. The capacitors 81, 81a may be varied to match the resistors 79, 79a in equalizing the E. M. F. induced in pick-up element 87 in its various positions of rotation.

The inductive elements 88, 88a of each filter, in conjunction with the inductive elements 87, 87a provide link coupling between the filters 77 and 77a respectively and tuned pick-up circuits 89, 89a. These tuned circuits are connected in series as shown so that the resultant output may be fed to a broad-band amplifier 90, capable of passing the highest desired harmonic of the blocking oscillator output. Means is thus provided for combining and amplifying harmonically-related E. M. F.s in different amplitudes and phase relationships for the production at the frequency of the blocking oscillator 76 of complex oscillations of any desired wave form.

Now comes the problem of changing the frequency of the wave thus produced to a desired frequency without changing substantially its harmonic content. I accomplish the change by the general method hereinbefc-re referred to.

A variable oscillator 95 determines the frequency of pulses generated by a pulse generator 96. This frequency is preferably variable throughout a range such that the difference between it and that of the blocking oscillator 76, may be varied from zero to whatever maximum fundamental frequency it is desired to produce from the synthesizer. Negative pulses from the generator 96 are mixed with the complex wave output from the broadband amplifier 90, as shown, and are fed to the cathode of a vacuum diode 97, which cathode is maintained at a positive potential with respect to ground by suitable means connected at 9S. Since the plate of the diode 97 is at ground potential, except when current is owing therethrough, the diode will conduct whenever the cathode is driven negative. Consequently, if the relationship between the complex wave, the positive bias and the pulse are such that the pulse drives the cathode negative during each pulse occurrence, the pulses of current through the diode 97 will be samples of the complex wave, taken at a slightly different point in each cycle of the complex wave. Providing a low-pass filter 99 greatly attenuates the pulse frequency, its harmonics and frequencies as low as one-half the pulse frequency and providing the one-half the pulse frequency, then the output of the filter will contain only the desired difference frequency and its harmonics and will be of substantially the same wave form as the original complex wave.

The wave thus produced may be amplified by an amplifier 100 and employed to modulate a crater lamp 8d or the like for the purposes discussed herein.

It will be obvious however, that the synthesizer itself has utility other than that discussed herein. For example, the output may be connected to an oscilloscope and to an electroacoustic translating system for demonstrating the sound of various complex waves.

Synthesizer synchronizing system In order to produce an integral number of cycles of a desired wave form during one revolution of a turntable or the like, so that a wave form or voice disc can be produced for use in a photoelectric musical instrument, it is necessary that the synthesizer used to produce a desired wave form be synchronized with the motor driving the turntable.

Since I have already described a system by means of which I can produce one revolution of a turntable during the occurrence of an integral number of periodic electric pulses, it will be obvious that if I synchronize the desired wave with the pulses, integral number of cycles of a desired wave form may be produced during one revolution. The essential elements of a system for accomplishing this result are shown in the area enclosed by the line 14a in Figure 15. What I do is to compare the frequency of pulses from a pulse generator such as 5a in Figure 7 with the difference between the fundamental frequency of the blocking oscillator 76 and the frequency of the variable oscillator 95. If they are not the same, I vary the frequency of the variable oscillator until they are the same, employing the following means: Referring to Figure 15, an L-C circuit 110, tuned to the fundamental frequency of the blocking oscillator 76, is connected as shown through a resistor 111 to the blocking oscillator. The voltage across circuit is fed through an amplifier 112 to the cathode of a vacuum diode 113 as shown. To the plate of the diode 113, through a small coupling capacitor 114 is fed a square wave from the variable oscillator 95, The resultant wave at the plate of the diode 113 is fed through a lowpass filter 115 similar to filter 99. The output of the filter 115 is a sine wave at the difference frequency between the fundamental of the blocking oscillator 76 and the variable oscillator 95. After amplification by an amplifier 116, the sine wave is mixed at the point 117 with the pulses with which the synthesizer is to be synchronized, and fed through a diode circuit 118 used to bias a reactance tube 119. If there is a difference between the pulse frequency and the difference frequency mixed at 117, the phase shift causes the D. C. level biasing the reactance tube to change and to vary the impedance offered by the tube across the tuned circuit of the variable oscillator 95, until the difference is zero.

Thus means have been provided for producing an integral number of cycles of a desired wave form during arevolution of a turntable or the like. It will be obvious then that I may employ this system in the production of voice discs of the type described in my copending application entitled Method and Means for Producing Tones and Voices Photoelectrically, Serial No. 117,239, filed September 22, 1949, now U. S. Patent No. 2,576,759 granted November 27, 1951. Such voice discs have a plurality of substantially radial series of wave-form patterns corresponding to the respective tone colors of a photoelectric musical instrument. Each series contains one or more cycles of a wave form for each concentric series of scanning slots in a rotating pitch disc. It will be obvious also that in order to provide wave-form patterns whose individual cycle lengths are exactly equal to the distance between scanning slots, it will be necessary to produce during one revolution of the disc upon which the wave forms are exposed, a number of cycles equal to the number of scanning slots in the corresponding series on the cooperating pitch disc. In the production of a wave form disc, I may mask that portion of the disc which is not to be exposed, leaving a space equal to a desired number of cycles for exposure by a light source whose intensity is varied in accordance with the desired wave form, or I may expose a complete circle of wave form patterns, using them as a master from which I make my wave form disc by exposure through the master of a desired number of cycles.

It will be obvious to those skilled in the art that the successful production of equally and accurately spaced narrow graduations produced by the methods described above, will depend upon a motor which revolves at an extremely constant speed.

In Figure 16, is illustrated such a motor. The rotor element 124 of the synchronous motor having an axle 125 is journaled for rotation by ball bearings 126 and 127 in a stator clement 128 mounted to a rigid support 129 by screws such as 130. The internal surface of the rotor 124 and the external surface of the stator y128 have equal numbers of rectangular shaped teeth such as indicated at 131 and 132 respectively. The windings 133 and 134,'to which the pulsating D. C. is supplied, are located in the stator as shown. The turntable 12b is mounted upon the top face of the rotor element 124 by means of screws such as 135. In order to reduce hunting in the turntable to a minimum, the turntable comprises a plate equipped with bosses 136 surrounded by a tubular member 137, preferably a standard bicycle tire which is filled with a viscous liquid such as glycerine as at 138. As is known in the art, the liquid-filled member.137 acts as a viscous damping means for reducing to a minimum periodic departures from synchronous speed caused by the rotor 124 hunting about its synchronous position with respect to the stator 128.

If there are any minor inaccuracies in the construction of the motor, which tend to produce periodic departures from synchronous speed, once during each revolution, a means must be provided to compensate for such departures; otherwise cumulative departures of graduations produced by means of the motor and a fiashing light would result. I have shown such a means in Figure ,16,

tuned respectively to the fundamental pulse frequency and its harmonics, said filters including variable irnpedance means and variable coupling means for controlling respectively the amplitude and phase relationship between said harmonics and the fundamental, a plurality of tuned circuits connected in series and coupled respectively to said filters, a variable oscillator, a second pulse generator' in connection therewith and generating pulses at a frequency determined by said variable oscillator, a mixer circuit connected between said tuned circuits and said second pulse generator for mixing the resultant voltage of said circuits with the pulses from said second generator, and a low-pass filter coupled to said mixer circuit and operative to attenuate all frequencies above substantially one-half the frequency of the pulses from said first pulse generator.

2. Means for synchronizing a synthesizer whose output frequency is equal to the difference between the frequency Vof its pulse generator and the frequency of its variable frequency oscillator with the frequency of periodic pulses from an outside source, comprising in coms bination a tuned circuit in connection with said pulse wherein a spring member 139 Vis supported under tension between a fixed pin 14D and a peg 141 eccentrically mounted to the axle 125 by an element such as the disc 142. It will be obvious that the peg 141 will be located at such a point and that the spring of 139 will be of such strength as to counteract the acceleration and deceleration caused by the mechanical inaccuracies referred to above.

Should the mechanical inaccuracies result in departures from synchronous speed which are not of a simple nature, a cam-actuated system may be employed to compensate for the complex variations. j

I have, as mentioned above, produced a circular trace on the tube T8 of Figure 7 for convenience in counting markers or pips for ascertaining dividing ratios between the low and high frequency oscillations. It will be obvious, however, that a sweep other than a circular one may be employed in such a system as described herein, once an approximate ratio has been established. For example, a horizontal trace could be produced in the usual manner, superimposing thereon vertical pips produced by the means shown in Figure 7.

In the description of my invention, 1 have referred to certain component circuits by names current in the art and readily recognized by the skilled worker. For the purpose of a complete disclosure, I may state that I may employ a phase shift network such as that illustrated in Figure 53, chapter l5 of Theory and Application of Electron Tubes by Reich, McGraw-Hill, second edition, 1944; and I may employ a liip-iiop multiple vibrator, such as that illustrated in Figure 7, chapter l() of the same volume and described in connection therewith; that the various pulse generators referred to hereinabove including the so-called wide pulse generator may be circuits, such as shown in Figure 16, chapter l() of the same volume; that a blocking oscillator as employed by me may haveV the construction illustrated in Figure 19, chapter 13 of Radar System Engineering, edited by Ridenour, McGraw-Hill, first edition, 1947; and that the amplifier and mixer 26a. employed by me embodies a circuit such as two conventional triode amplifiers, the plates of which are connected in parallel to an output circuit, the oscillations to be mixed being fed to the'respective grids of the tri-ode amplifiers.

Modifications may be made in my invention without departing from the spirit of it. Having described my invention in certain exemplary embodiments, what I claim as new and desire to secure by Letters Patent is:

l. In a. harmonic synthesizer, the combination of a source of fixed frequency oscillations, a first pulse generator in connection therewith, the frequency of the pulses Series of filters coupled to said first pulse generator and generator and tuned to the fundamental frequency of the pulses generated thereby, means coupled to said tuned circuit for amplifying the potential across said tuned circuit, a diode circuit in connection with said variable frequency oscillator an-d said amplifying means for mixing the respective o-utputs thereof, a filter in connection with said diode circuit for passing the difference frequency between said generator and saidoscillator, amplifying means in connection with said filter for amplifying said difference frequency, a second diode circuit coupled to said last-mentioned amplifying means and said outside source yfor mixing the output of said last-mentioned amplifying means and said pulses from said outside source, a reactance tube circuit in connection with said diode 'circuit and biased thereby by a potential which is directed proportional to the difference in phase between the frequency of said outside pulses and said difference frequency, said reactance tube being in connection with said variable oscillator and operative to modify the frequency generated thereby to bring the dierence frequency into equality with said outside pulse frequency.

3. A system for producing a complex wave of a desired form whose fundamental frequency component is at the same frequency as that of control pulses from an outside source, comprising a harmonic synthesizer and a synchronizing circuit connected between said outside source and said synthesizer, said synthesizer comprising the lcombination of a source of fixed frequency oscillations, a first pulse generator in connection therewith, the frequency of the pulses generated thereby being determined by said last-mentioned source, a series of filters coupled to said first pulse generator and tuned respectively to the fundamental pulse frequency and its harmonics, said filters including variable impedance means and variable coupling means for controlling respectively the amplitude and phase relationship between said harmonics and the fundamental, a plurality of tuned circuits connected in series and coupled respectively to said lters, a variable oscillator, a second pulse generator in connection therewith and generating pulses at a frequency determined by said variable oscillator, a mixer circuit connected between said tuned circuits and said second pulse generator for mixing the resultant voltage of said -circuits with the pulses from said second generator, and a low-pass filter coupled to said mixer circuit and operative to attenuate all frequencies above substantially onehalf the frequency of the pulses from said first pulse generator, said synchronizing circuit comprising the combination of a tuned circuit in connection with saidfirst pulse generator and tuned lto .the frequency of the pulses generated thereby, means for amplifying the potennal across said tuned circuit, a diode circuit in connection with said kvariable oscillator and said amplifying means for mixing the respective outputs thereof, a filter in connection with said diode circuit for passing the diterence frequency between said pulse generator and said oscillator, amplifying means in connection with said filter for amplifying said dierence frequency, a second diode crcuit for mixing the output of said last-mentioned amplifying means and said pulses from said outside source, a reactance tube circuit in connection with said diode cir cuit and biased thereby by a potential which is directly proportional to the diierence in phase between the frequency of said outside pulses and said difference frequency, said reactance tube being in connection With said variable oscillator and operative to modify the frequency generated thereby to bring the difference frequency into equality with said voutside pulse frequency.

References Cited in the le of this patent UNITED STATES PATENTS 2,075,802 Davis Apr. 6, 1937 2,121,359 Luck et al. June 21, 1938 2,164,809 Fisher July 4, 1939 18 Norton Mar. 11, Mathes et al. Mar. 3, Schlesinger lune 6, Hassler Feb. 18, Jones Apr. 13, Ranger Nov. 2, Hallmark Jan. 18, Bliss Dec. 6, Young Dec. 6, Goldberg Feb. 7, Wood Mar. 28, Grosdoff Sept. 12, Sziklai Nov. 28, Hugenholtz Feb. 6, Wickham Feb. 6, Ranger Feb. 27, McFarlane June 12, Hammond Aug. 7, Hester Apr. 22, Gray June 24,

Garman et al. July 22,

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