US2481886A - Frequency modulation reproducing system - Google Patents

Description

Sept. i3, 1949. c. M. slNNETT FREQUENCY MODULATION REPRODUCING SYSTEM 2 Sheets-Sheet l Filed Sept. 25. 1942 CAPACITY PICKUP FREQU ENCY 0f DISCRIMINATOR CIRCUIT MPLIFIER INVENTOR CHT-:STR slNNl-:TT BY ATTORNEY n c. M. slNNl-:TT FREQUENCY MODULATION REPRODUCING SYSTEM Sept. 13, 1949.

2 Sheets-Sheet 2 Filed Sept. 23. l194:2

ooo

CHESTER M. SANNETTv .CZD n.3 xvi ...@Www

Patented Sept. 13, 1949 FREQUENCY MODULATION REPRODUCING SYSTEM Chester M. Sinnett, Westmont, N. J., assgnor to Radio Corporation of America, a corporation of Delaware Application September 23, 1942, Serial No. 459,375 2z claims.` (c1. 17a-400.4)

My present invention relates to systems for reproducing sound waves, and more particularly to systems employing frequency modulated signals for producing audio frequency waves.

In the past, it has generally been proposed to reproduce recorded sound waves, such as phonograph records, by translating the record impression into a reactance variation, the reactance variation being employed to modulate a high frequency oscillator. The modulated high frequency oscillations have been demodulated, and the resulting modulation energy has been reproduced. More specifically it has been proposed to utilize, in connection with a phonograph record, a pickup device of the electrostatic type, variations in magnitude of the capacity being employed to vary the frequency of the high frequency oscillator in accordance with the modulation amplitude. The frequency modulated wave energy has been converted into corresponding amplitude modulated wave energy, and the latter has been rectified so as to permit reproduction of the original modulation signals.

In these systems of the prior art various disadvantages and defects have become manifest. The ideal type of reproducing system of the frequency modulation type should be highly sensitive, of high fidelity, and yet compact and economical. In reproducing audio frequencies up to 10,000 or 12,000 cycles Without the introduction of objectionable surface noise, there are various factors that must be considered. The design of the pickup is very important. Generally, it can be stated that a phonograph pickup suitable for a high fidelity system should provide a frequency response throughout the usual audio frequency range, which is proportional to either the amplitude or the velocity of the modulation in the record groove. The sensitivity of the pickup should be such that the amplification required between the pickup and the loud speaker is not so great as to introduce serious microphonic difliculties.

It may be stated to be one of the main objects of my present invention to provide a frequency modulation network for use with a simple specially designed pickup, which is adapted to reproduce lateral cut records, there being provided a frequency modulated signal which has suflicient frequency deviation to provide a relatively high audio frequency output when applied to a simple and economical type of frequency discriminator and rectifier.

It is an important object of this invention to provide a frequency modulation network for a capacity pickup device of the ribbon type; the frequency modulation network being characterized by its ability to produce a relatively high audio frequency output in an economical manner; the frequency modulation network consisting of a tube which has a section thereof functioning as a high frequency oscillator of essentially constant amplitude and whose frequency is deviated by capacity variations in the capacity pickup, and there being developed in the plate circuit of the tube frequency modulated oscillations which are subsequently converted into audio modulation signals corresponding to the originally recorded audio signals.

Another object of this invention is to provide a frequency modulation system which can be generally employed for any source of audio energy which is utilized in conjunction with a reactance device, whereby the audio energy is converted into reactance variations; the reactance variations being transformed into high frequency oscillator frequency variations, and a simple resonant circuit being used as the means for converting the oscillator frequency variations into changes in the amplitude of signals to be applied to a simple diode.

Still another object of my invention is to provide a relatively inexpensive and highly sensitive device for reproducing phonograph records, wherein there is provided an oscillator tube which provides electronic coupling between a frequency modulation oscillator section and a simple discriminator circuit arranged in the output circuit of the oscillator tube.

Yet other objects of my invention are to provide phonograph record reproducing systems wherein one or more elements of the reproducing circuits may be located upon the tone arm of the phonograph. v

Still other objects of my invention are to improve generally the simplicity, efficiency and reliability of recorded sound wave reproducing systems, and more especially to provide a frequency modulation reproducer for sound records which is not only capable of producing high fidelity reproduction substantially free of surface noises, but which secures such reproduction in a highly economical manner.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims; the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically several circuit organizations whereby my invention may be carried into effect.

In the drawing:

Fig. 1 shows a circuit embodying the invention,

Fig. 2 shows the resonance curve of the dis criminator circuit',

Fig. 3 shows the tone arm with all the elements of the circuit of Fig. l mounted on the tone arm,

Fig. 4 illustrates a modiiied form of construction wherein solely the oscillator tube is mounted on the tone arm,

Fig. 5 shows the circuit diagram of the modification shown in Fig. 4.

Referring, now, to the accompanying drawings, wherein like reference characters in the various figures designate similar circuit elements, there is shown in Fig. l a circuit diagram of a preferred formof the invention. By way of example, the invention is shown applied to a capacity pickup device. The latter is to be understood as being adapted for cooperation with a, phonograph record of the usual type. The pickup generally comprises a fixed electrode I spaced from a movable electrode 2. The spaced electrodes I and 2 provide a condenser whose capacity varies in accordance with the motion of' a stylus secured to the mobile electrode. The pickup is schematically represented. It is not a part of this invention, and reference is made to my application Serial No. 414,305, led October 9, 1941, now Patent No. 2,376,456, granted May 22, 1945, for a complete disclosure of the manner of constructing the pickup device.

The electrode I may be an insulated brass plate mounted on a metal frame, and the plate acts as the high potential side of the pickup. To the metal frame may be secured a thin metal ribbon, the latter may be in a plane parallel to the 'electrode I. The ribbon is placed under tension in order to increase the natural resonance frequency of the pickup. Preferably, the natural frequency is above 10,000 cycles. Displacement of the stylus laterally, as when running through the record grooves, results in a change in the position of the ribbon with respect to the xed electrode.

The ribbon, or mobile, electrode 2 is the low potential side of the pickup. If desired, the mobile electrode could be the high potential side of the pickup device. Displacement of electrode 2 causes a change in the capacitance of the pickup. A coaxial cable is employed to couple the pickup to the input electrode 3 of oscillator tube 4. The cable may be a high impedance line. The tube 4 is a tube of the 6SA7 type; it has a cathode 5, a plate 5 and five control grids arranged successively in the electron stream to the plate. Control grid 3 acts as the oscillator input grid. The second, third and fourth grids are tied together; they are designated by the numeral 'I since they effectively function as a single electrode. The electrode 'I acts as the oscillator anode. Suppressor grid 8 is grounded inside the tube envelope. Electrodes 'I and 8 function to diminish any tendency for capacitive coupling between the oscillator and the output.

The coaxial cable has its grounded sheath 9 connected to the mobile electrode 2, while the axial conductor II) connects the fixed electrode I to the high alternating potential side of the coil II. The latter is preferably of the powdered-iron core type. The cathode 5 is returned to an intermediate point on coil II, the latter point being any desired point above the grounded end of the coil which will produce high frequency oscillations. The adjustable, powdered-iron core of the coil is conventionally represented. The grid 3 is connected to the axial conductor I Il by conden-ser I2 and resistor I3. returns the grid to ground.

The coil II is resonated to a desired, mean frequency Fc by the combined normal capacity of the pickup and the distributed capacity of the ,coaxial line. Merely by Way of example, Fc may he given a value of 30 megacycles (mc). It is to be understood that when the stylus is in its normal position, then the oscillator tuned circuit has the value Fe. Capacitance variations of the pickup, are translated into frequency variations of the constant amplitude, high frequency oscillations produced by oscillator 5-3-1. The anode I is connected to a source (+B) of direct current through the resistors I4 and I5; the condenser I6 bypasses the upper end of resistor I4 for high frequency cur-rents. In place of the pentagrid tube there may be used a 6J7 type of tube., In the latter, a pentode, only a single screen grid isl employed between control grid and suppressor grid.

The natural period of the pickup I -2 may aid in the production of high audio frequency gain. By using a period above 10,000 cycles the audio gain of the system may be highly improved, while the circuit elements are kept relatively inexpensive. To increase the radio frequency gain, the oscillator section of the tube 4 is electron-coupled tc the plate circuit. Frequency modulation of the oscillations is produced by virtue of the variations in capacity of the oscillator tank circuit.

The recorded sound waves are converted into capacity variations by the pickup device. Hence, the latter variations act to vary the frequency of the high frequency oscillations in accordance with the amplitude of the recorded sound waves. The rate of frequency deviation is a function of the audio frequencies per se. The extent of frequency deviation, or swing, is dependent upon the audio amplitude. The maximum deviation may be as high as 1 5 kilocycles (kc.) to either side of Fe, the center frequency. Of course, the deviation may Vary depending on the value of the chosen mean frequency. The generic expression angular velocity-modulated is used herein to designate that the modulation of the high frequency oscillations may be either frequency or phase. The latter type cf modulation differs only in that the rate of deviation for higher audio frequencies is greater. Furthermore, it is to be clearly understood that this circuit is equally applicable to any desired type of audio frequency energy source. For example, a microphone pickup may replace the phonograph pickup. Further, the microphone may be one used in hearing-aid apparatus, public address systems, binaural systems and the like. There are many other applications such as pressure devices, liquid height measuring devices, elongation measurement, vibration measurement, etc. in which the invention may be incorporated.

Those skilled in the art are fully acquainted with the phenomenon of electron coupling between an oscillator section of a tube and a more remote positive electrode thereof. It is believed sufficient for the purpose of this application to point out that the circuit connected to plate 6 has produced therein the frequency modulated oscillations by virtue of electron coupling between the oscillator section of tube 4 and plate E. A relatively simple and inexpensive type of` discriminator circuit is provided to transform the frequency modulated oscillationsinto corresponding amplitude modulated oscillations. During this transformation process the frequency deviation of the frequency modulated wave energy is translated into corresponding amplitude modulated waves.' This discrimination action is well known. The discriminator circuit comprises the powderediron core coil I 1 connected in shunt with condenser I8. The high alternating potential side of circuit I'I-I 8 is connected to plate E. The lower end of coil I'I is connected by resistor I9 to the junction of resistors I4 and I5. The junction of resistors I4 and I5 is bypassed to ground for high frequency currents by condenser 2B, and condenser 2l connects the low potential side of coil I1 `to ground for high frequency currents.

The discriminator circuit I'I-l8 isvmistuned with respect to Fc. In other words, and referring to Fig. 2, the peak resonance frequency of circuit I'I-IB may be higher than the frequency Fc of the oscillator tank circuit. Fig. 2 shows that Fc may be located along the slope of either flank of the resonance curve of discriminator circuit I'I|8. Preferably, it is desirable to adjust the iron core of coil I'I so that the resonant frequency of the discriminator circuit is such that the mean oscillator frequency falls at approximately the 70% response point on one side of the selectivity characteristic shown in Fig. 2. Hence, the subsequent rectifier will have an input circuit whose operating point is along a linear portion of a singlo-peak resonance curve. It will be recognized that such operation results in translation of the frequency modulated wave energy into correspending amplitude modulated wave energy.

It is desirable, of course, that the selectivity characteristic, or the Q of the circuit, be so chosen that the slopes of the resonance curve are as linear as possible. Rectification of the amplitude modulated wave energy is effected by a sirnple diode circuit. To secure further economy of elements with high audio gain, there is employed a diode-triode of the 6R7 type. The numeral 22 designates such a tube. The latter comprises a cathode 23. an anode 24, control grid 25 and a plate 2S. The anode 24 and cathode 23 function as the rectier diode. The anode 24 is connected to its cathode through a series path comprising a radio frequency choke coil 21 and load resistor 28. and across the resistor there is developed the modulation voltage. nected from the lower end of coil 21 to ground, and bypasses all high frequency components. The condenser 30 couples the upper end of coil 21 to the high potential side of the discriminator circuit III8.

The audio modulation voltage, which is developed across resistor 28. is amplied in the triode section of tube 22. This is accomplished by connecting grid 25 to the anode end of resistor 28 through coupling condenser 3|, resistor 32 con- 'P necting the grid 25 to the grounded end of the cathode biasing resistor 33. The plate'2B may be connected through the output load resistor 34 to the junction of resistors I4 and l5. In this way there is secured a considerable increase in audio voltage, and the amplied audio voltage signals developed across resistor V34 are transmitted to a subsequent utilization network. The latter may comprise additional stages of audio amplification Y followed by a proper reproducer. It is pointed out' The condenser 29 is conthat with this type of system the general hum level is acceptable, and microphonics are reduced to a very lowvalue. Needle noise is substantially eliminated, and reproduction of the recorded sound waves, whether music or speech, is of extremely high fidelity. It is also pointed out that the tubes 4 and 22 employed herein are of commercially available types, and are relatively inexpensive. Indeed, it can be stated that the cost of manufacture of the present reproducing system is many times less than that of the conventional record reproducers able to approach the high fidelity of reproduction of the present system.

There are advantages in mounting the various circuit components upon the tone arm of the phonograph, and in close proximity to the pickup device. In Fig. 3 I have shown one manner of mounting the circuit components on the tone arm. It is not believed necessary to describe Fig. 3 in detail, since it is self-explanatory. Each of the corresponding circuit components of Fig. 1 has been appropriately labeled. The pickup device and its attachment are not shown in the figure, since such feature is not a part of the preesnt invention. Reference is made to my aforesaid application for such details. However, it will be observed that it is possible to mount all the circuit components upon the tone arm, and in that way it is possible to economize on space in the apparatus.

Where it is not desirable to locate the circuit components as shown in Fig. 3, it may still be desirable to mount the oscillator tube directly on the tone arm. For example, a construction as shown in Fig. 4 may give relatively greater freedom from extraneous noises. Furthermore, increased stability may also be secured by locating only the pickup device and the oscillator tube on the tone arm. It is not believed necessary to describe the construction of Fig. 4 in detail, since the iigure is self-explanatory with reference to Fig. 5.

In Fig. 5 I have shown the circuit which would be employed with a tone arm arrangement such as shown in Fig. 4.V Generally, the circuit elements of Fig. 5, which are similar to those of Fig. l, bear corresponding numerals. The essential feature of Fig. 5 is the utilization of a low impedance line for connecting the tuned plate circuit of tube 4 to the discriminator circuit which is mounted on the amplifier chassis. The high impedance connection in Fig. 4 is shown running through successive damping blocks made of resilient insulation material. The oscillator tube projects far enough to permit removal without having to take the cover off.

Considering Fig. 5 more specifically, the oscillator coil II is tuned by the capacity of pickup 2-'I to the center frequency Fe. It will be understood that in this case the coaxial cable S-I is not employed. The plate coil I'I' is of the powdered-iron core type. The distributed capacity of coil I I is used to resonate the coil to the proper frequency. It would also be possible to resonate this circuit by lumped capacity. The iron core is adjusted so that the coil is tuned to Fc.' The rectier-audio ampliiier tube 22 has its diode rectifier electrodes coupled with the discriminator coil 4l). I'his coil is tuned by its distributed capacity. Again, a lumped capacity could be used in addition to distributed capacity. The iron core is adjusted so that the mean frequency Fc is located as shown in Fig. 2. The audio voltage developed across load resistor 28 is amplified in the triode section of tube 22. The low impedance line 50 couples coils II' and 40. f

yThe low impedance transmission line may comprise a pair of twisted wires. The terminal coil ateach end ofthe linelil is coupled to the respective coils IT and 40,. and vone' of the leads adjacentto these' terminal coils is grounded at eachl end. The'plate and oscillator anode electrodes of tube d are connected to' the +B voltage terminal of the direct current energizing source. It will be noted that the positive voltage line Sil' runs along the tone arm, then parallel to the low impedance line, and then into the amplifier housing ii). Similarly, the heater line B for tube 4 runs along the tone arm, then parallelV to lines B and', and then into the amplier' housing lll).v The dotted line rectangle 90 designates the tone arm, while the dotted line rectangle 'lt denotes the amplifier housing. Comparison between Figs. 4 and 5vwill readily show the manner in which the various energzing connections are made from the tone arm to the amplier housing. These figures, also, show the general location of the low impedance line.

By the term low impedance line is meant a line whose impedance isloW compared to the high impedance line shown connected between the pickup unit and the oscillator tube input grid.v It is advantageous to use the low impedance twisted pair of wires 5l), because the line may be located and positioned in any desired Way (as in Fig. 4) Without causing reiiection along itself. If the line 59 were of a high impedance', as in the case of the line running from the pickup, then it would have to be carefully protected. The tubing support of the tone arm would have to be designed for it.

Comparing the circuit of Fig. 5 with that of Fig. 1, it will be noted that in Fig. 5 the oscillator plate circuit has frequency modulated os.- cillations developed across the resonant coil I1' Yby virtue of electron coupling from the oscillator section of the tube to its plate circuit. -Discrimination is obtained by mistuning resonant coil 4U inthe diode circuit. In Fig. 1 the mistuned discriminator circuit I'l-l8 is located directly in the oscillator plate circuit. It is to be clearly understood that itis within the scope of my present invention to remove from the tone arm all of the circuit components, except the pickup device. In other Words, and referring to the circuit of Fig. 1, all the circuit components shown in the latter may be mounted within a common housing, While the capacity pickup deviceV |-2 is mounted directly on the tone arm.

While I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and. described, but that many modications may be made without departing from the scope of my invention.

What I claim is:

1. In combination with a variable capacity pickup device for reproducing phonograph records, an oscillator tube provided with electrodes forming an oscillator section; a resonant circuit tuned to a high predetermined mean frequency coupled to said oscillator electrodes for generating high frequency oscillations, said pickup device being connected as part of said resonant circuit whereby variations in pickup capacitance result in frequency modulation of the high frequency oscillations about said mean frequency; said tube including a positive output electrode Which is electron coupled to said oscillator section; a resonant discriminator circuit connected to said, positivev output electrode, said discriminator circuit having frequency response characteristics exhibiting a maximum and sloping away on both sides of said maximum; said mean frequency lying at an intermediate portion of one of said sloping sides; and a rectifier connected directly across said discriminator circuit.

2. In combination with a variable capacity pickup device for reproducing phonograph records, a space discharge tube provided with electrodes forming an oscillator section; a resonant circuit tuned to a predeterminedmean frequency coupled to said oscillator electrodes for generating high frequency oscillations, said pick-up device being connected as part of said resonant circuit whereby variations in pickup capacitance result in frequency modulation of the high frequency oscillations about said means frequency; said tube includneva positive output electrode which is electron coupled to said oscillator section; a resonant discriminator circuit connected to said positive output electrode, said discriminator circuit` having frequency response characteristics exhibiting a maximum and sloping away .on both sidesof said maximum; said mean frequency lying at an intermediate portion of one of said sloping sides; and a rectifier tube coupled to said discriminator circuit; said tubes, pickup device and resonant circuits being held on a phonograph tone arm.

3. In combination, a phonograph tone arm provided with a variable reactance phonograph pickup device; a space discharge tube provided with an oscillator section and a positive output electrode, said pickup device being connected as part of an oscillator network to said oscillator section to provide angular velocity-modulated oscillations which have Aa predetermined mean frequency; a resonant circuit coupled to said output electrode and tuned to said mean frequency; electron coupling with said oscillator section through said space discharge tube, to develop amplified angular velocity-modulated oscillations in said resonant circuit; a line linking said output resonant circuit with another resonant circuit tuned to a frequency substantially different from said mean frequency to function -as a discriminator circuit; and a rectifier connected to said discriminator circuit; said oscillator tube being mounted on the tone arm.

4. In combination, a space discharge tube provided With an oscillator section and a positive plate electrode; a variable capacity pickup connected as part of an oscillator network to said oscillator section to provide frequency-modulated oscillations which have a predetermined mean frequency; a resonant circuit coupled to said plate electrode for electron coupling with said oscillator section through said space discharge tube to develop said modulated oscillations in said resonant circuit; said resonant circuit being tuned to a frequency suiciently different from said mean frequency to function as a discriminator circuit; and means coupled to said discriminator resonant circuit for rectifying amplitude modulated Wave energy appearing across the discriminator circuit.

5..In combination with a variable capacity pickup device for reproducing phonograph records, a space discharge tube provided with electrodes forming an oscillator section; a resonant circuit tuned to a predetermined mean frequency coupled to said oscillator electrodes for generating high frequency oscillations; said pickup device forming part of said oscillation resonant circuit whereby variations in pickup capacitance result in frequency modulation of, theA high frequency oscillations; a discriminator consisting of solely a passive resonant network; means providing electron coupling between the discriminator network and said oscillator section, said discriminator network having frequency response characteristics exhibiting a maximum and sloping away on both sides of said maximum; said mean frequency lying at an intermediate portion of one of said .sloping sides; and a rectifier coupled to said discrirninator network.

6. In combination with a variable capacity pickup device for reproducing phonograph records, a space discharge tube provided with electrodes forming an oscillator section; a resonant circuit tuned to a high predetermined mean frequency coupled to said oscillator electrodes for generating high frequency oscillations; said pickup device forming part of said oscillation resonant circuit whereby variations in pickup capacitance result in frequency modulation of the high frequency oscillations, said tube including a positive output electrode electron coupled to said oscillator section; a sloping filter discriminator circuit connected to said positive output electrode, said mean frequency lying at an intermediate portion of the slope of said lter; and rectier means coupled to said discriminator circuit.

7. In combination with a variable capacity pickup device for reproducing phonograph records, a space discharge tube provided with electrodes forming an oscillator section; a resonant circuit tuned to a high predetermined mean frequency coupled to said oscillator electrodes to provide high frequency oscillations, a high im'- pedan-ce line connecting said pickup device in said resonant circuit whereby variations in pickup capacitance result in frequency modulation of the high frequency oscillations; said tube including a positive output electrode electron coupled to said oscillator section; a discriminator circuit, a relatively low impedance line coupling said positive output electrode to the discriminator circuit; said discriminator circuit having frequency response characteristics exhibiting a maximum and sloping away on both sides of said maximum; said mean frequency lying at an intermediate portion of one of the sloping sides; and rectifier mea-ns coupled to said discriminator circuit.

8. In combination with a variable ycapacity pickup device for reproducing phonograph records, a space discharge tube provided with electrodes forming a high frequency oscillator; a resonant circuit tuned to a high predetermined mean frequency coupled to said oscillator electrodes to provide high frequency oscillations; said pickup device being coupled by a high impedance line to form part of said resonant circuit whereby variations in capacitance result in frequency modulation of the high frequency oscillations; said tube including a positive output electrode electron coupled to said oscillator; a discriminator circuit connected to said output electrode, said discriminator circuit having frequency response characteristics exhibiting a maximum and sloping away on both sides of said maximum; said mean frequency lying at an intermediate portion of one of the sloping sides; a diode rectifier coupled to said discriminator circuit; and a relatively low impedance line coupling said positive putput electrode to said discriminator circuit.

.9. A system for reproducing signals from a record wherein said signals are recorded as undulatory impressionszrin the record, comprising: means for producing oscillatory waves of a predetermined high meanfrequency; a variable capacity pickup device having a stylus adapted to vibrate in response to said record impressions to thereby produce variations in pickup capacitance `representative of said signals; means for frequency modulating ,said high frequency waves in response to said capacitance variations; a passive frequency discriminator network coupled to said wave producing means for translating the frequency modulated waves into corresponding amplitude modulated waves of like mean frequency; means providing electron coupling between saidwave producing means and said passive discriminator network; and means for deriving from said amplitude modulated waves signals corresponding to said desired modulation signals.

10. A system for reproducing signals from a record wherein said signals are recorded as undulatory impressions inthe record, comprising: means for producing oscillatory waves of a predetermined highmean frequency; a variable capacity pickup device having a stylus adapted to vibrate in response to. said record impressions to thereby produce variations in pickup capacitance representative of said signals; means for frequency modulating said high frequency waves in response to said capacitance variations; a passive frequency discriminator network coupled to said. wave producing means for translating the frequency modulated waves into corresponding amplitude modulated waves of like mean frequency; means providing electron coupling between said wave producing means and said passive discriminator network; and means for deriving from said amplitude modulated waves signals corresponding to said desired modulation signals, said oscillatory waves having a mean frequency of the order of 30 megacycles per second, and said frequency modulating means causing the oscillatory waves to be deviated in frequency up to l5 kilocycles per second'vto either side of said mean frequency.

il. A system for reproducing signals in the form of undulatory impressions on a record, comprising: means for producing oscillatory waves of a predetermined high mean frequency; a variable capacity pickup device having a stylus adapted to vibrate in response to said record irnpressions to thereby produce variations in pickup capacitance representative of said signals; means for frequency modulating said high frequency waves in response to said capacitance variations; a passive ,frequency discriminator network coupled to said wave producing means for translating the frequency'modulated waves into corresponding "amplitude modulated waves of like mean frequency; means providing electron coupling between said wave'producing means and said passive discriminatorV network; means for deriving: from said amplitude modulated waves signals corresponding to said desired modulation signals and a tone arm supporting said pickup device and at least said oscillatory wave producing means.- l

12. In combination with a reactance pickup device for sound records, an electron discharge tube provided with a cathode, control grid and positive electrode cooperating to function as an oscillator section, an additional positive electrode inpsaid tube functioning as an output electrode.

'a 'resonant circuit coupledto the oscillator section electrodes, said resonant circuit being tuned to apredeterminedV high frequency, means connecting said pickup device .tosaid resonant circuit whereby variations in `pickup reactance result in frequency modulation of oscillations produced by said oscillator section, a resonant output circuit connected to said positive output electrode, said oscillator section being electron coupled to said positive output electrode whereby said frequency modulated oscillations are applied in amplified form to the output electrode circuit.

13. In combination with a reactance pickup device for sound records, an electron discharge tube provided with a plurality of electrodes forming an oscillator section, a resonant -circuit tuned to a predetermined high frequency coupled to said oscillator electrodes, said pickup device being connected to said resonant circuit whereby variations in pick-up reactance result in frequency I modulation of high frequency oscillations, said tube including a positive output electrode which is electron coupled to said oscillator section, a discriminator circuit connected to said positive output electrode,` said discriminator circuit being A tuned to the peak frequency of a resonance curve, said predetermined high frequency lying at an intermediate portion of one of the slopes of said resonance curve, anda rectifier coupled to said discriminator circuit.

14. In a signal vibration reproducing system: an electron coupled oscillatorA including an electron emissive cathode electrode, an electron collecting electrode, and electron flow controlling means including at least one electrode grid between the cathode and the collecting electrode; oscillation supply means including an oscillation frequency controlling resonant circuit having variable reactance pick-up structure connected for responding to `vibrational signal variations by correspondingly varying its reactance and the tuning of theresonant circuit in accordance with said signal variations to produce variable frequency oscillations in which the frequency vlbration correspond to signal variations; and output means connected to the electron collecting electrode for utilizing the amplified variable frequency oscillations developed through the electron coupling between the oscillation supply means and the electron collecting electrode; said output means including demodulating means for deriving the signal variations from the lvariable frequency oscillations.

15. The combination asdefined by claim 14 in which the resonant circuit isdirectly coupled to the electrode grid; the demodulating means is in the form of resonant sloping filter means tuned to a frequency different from the mean frequency of the oscillations; andthe electron flow controlling means includes at least one additional electrode grid between the collecting electrode and the grid coupled'tothe resonant circuit, said additional grid rbeing connected for improving the passage of electrons through the grids to the collecting electrode and diminishing the capactive coupling between adjacent tube elements.

16. The combination as defined by claim 15 in which four electrode grids are :positioned between the collecting electrode and the grid coupled to .the resonant circuit, and said four :grids are all connected for diminishing the capactive coupling between the collecting electrode .and the grid coupled to the resonant circuit.

17. The combination as defined by claim 14 in which the demodulating means includes sloping 12 filter elements cou-pled to produce variable am.- plitudes of response in accordance with variations in output signal frequency.

.18. The `combination as defined by claim 14 in which the output means include high impedance oscillation transfer elements and a .coupling line having a low impedance with respect to the high .impedance elements, coupling the collecting electrode to the demodulating means.

19. The combination as defined by claim 14 including a movable tone arm holding the pick-up structure, the pickup structure having .of the undulatingly grooved record reproducing type lncluding a stylus for guiding the structure along the grooves of the record to vary the pickup reactance in accordance'with groove undulations; at -lleast part of the Vbalance of said reproducing system being also held on said arm.

20. In a phonograph record reproducing sysa tem for reproducing signals recorded as undulatory grooves on a solid record: a movable tone arm carrying variably reactive pickup elements including a guide stylus .for guiding the pickup elenients along the grooves and moving the tone arm accordingly; transducing means including khigh-frequency oscillation generating structure for developing frequency. modulated electric waves in which the frequency modulations .corresponds to the signal undulations; and demodulating means for deriving electrical signals corre,- sponding to the record signals from the frequency modulated electric waves; said oscillation generating structure being held by said movable tone arm relatively fixed and in relatively close proximity with respect to the pickup elements.

` 21. In a signal vibration reproducing system: an amplifying electron discharge tube including an electron emissive cathode, an electron collecting electrode, and electron flow controlling means for electrically influencing the movement of electrons from the cathode to the collecting electrode where they deliver currents corresponding to amplification vof the electrical flow controlling ln.- uences; said flow controlling means including at least one electrode grid between the cathode and the collecting electrode; oscillation supply means comprising resonant circuit elements, including inductance and capacitance, coupled with said flow controlling means for producing frequency modulated oscillations corresponding to the signal vibrations in the movement of. electrons; said kresonant circuit element being connected to lfeed back some `of the amplified energy in the electron 4flow to the flow controlling means for producing said oscillations; and output means connected to the electron collecting electrode for electron coupling with said oscillation supply means and developing amplified frequency modulated oscillations; said output lmeans including demodulating means for deriving a signal corresponding to the frequency modulations.

272. In a signal vibration reproducing system; an amplifying electron Vdischarge tube including 'an yelectron emissive cathode, an electron collecting electrode, and electron ow controlling means 'for `electrically influencing the movement o f electrons lfrom the cathode to the collecting electrode Where lthey deliver currents corresponding to ampli'ication of the electrical flow controlling in.-

fluences;v said flow controlling means'including at least three electrode grids between the cathode and the collecting electrode; oscillation supply means coupled -to some of said electrode grids to provide an oscillator tube section producing frequency modulated oscillations corresponding to the signal vibrations in the movement of electrons; said oscillation supply means being connected to feed back some of the amplified energy in the electron flow to the ow controlling means for producing said oscillations; at least one of said grids being interposed between the collecting electrode and said oscillator tube section and connected to improve the electron flow therebetween; and output means connected to the electron collecting electrode for electron coupling with said oscillation supply means for developing amplified frequency modulated oscillations; said output means including resonant circuit demcdulating means for deriving a signal corresponding to the frequency modulations.

CHESTER M. SINNETT.

REFERENCES CITED The following references are of record in the ille of this patent:

Number Number 14 UNITED STATES PATENTS Name Date Loewe Aug. 17, 1926 Dow July 23, 1935 Zakarais July 16, 1940 Crosby Feb. 4, 1941 Zakarias May 13, 1941 Farnsworth Dec. 8, 1942 Unger Jan. 23, 1945 FOREIGN PATENTS Country Date Great Britain Dec. 31, 1932

Images