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Oct. 1, 1946. A_ w, WELLS I 2,408,589 APPARATUS FOR PRODUCING ELECTRICAL OSCILLATIONS Filed May 15. 1942 3 Sheets-Sheet 2 RESISTOR ao\ ' PHu'ru ELECTRIC csu. ‘ 7 noun/322R :Q as ___47"" ‘?y-=7 E’) ' /\l\/ ~59’® Q - *JO DLAVIER KEY 41 / LR 42 A .\‘ _ /v\ m _ / 4% / _ _ / __ ‘ \__~ \_'/__ I . F196 . lF'HUTEI voL-rAuc TYPE. FELL /46 'F + -' l +9 519$ a. I 1| 7" II II In II II n’ H II II Jnucnlot ?lvijz/ W Wells. @541’ . aw I. Oct; 1, 1946- ' A; w. WELLS 2,408,589 . APPARATUS FOR PRODUCING ELECTRICAL dscILLATIoNs Filed May 13. 1942 .. Q '_ C 3 Sheets-Sheet 5 I - _ 3mm ‘7/ ?lviiz/ 14/. Weds. 2,408,589 Patented Oct. 1, 1946 UNITED STATES PATENT OFFICE 2,408,589 APPARATUS FOR PRODUCING ELECTRICAL OSCILLATIONS Alvin W. Wells, Chicago, Ill., assignor of one-half to Jewel W. Wells, Decatur, Ill. Application May 13, 1942, Serial No. 442,804 3 Claims. (01. 25041.5) 1 The present invention relates to a system or method and apparatus for the production of'clec trical oscillations, and relates more particularly to an electrical system which uses as a source of‘ 2 buffer ampli?ers for each glow discharge oscil lator to thereby separate the electrical circuits of each oscillator from one another when two or more of the oscillators are simultaneously con nected or keyed to the output. Since the elec trical instrument may contain from sixty-one to several hundred oscillators, in order to afford a It is an important object of my invention to satisfactory tonal range, the practice of using provide a method and apparatus for'producing separate oscillation or buffer ampli?ers for each electrical oscillations as obtained from one or more glow discharge oscillators which may be ad 10 oscillator would render the musical instrument very expensive and complicated to manufacture. vantageously and economically used in the manu By my invention, I have provided a method facture of an electric musical instrument, such and apparatus for coupling two or more glow as an electric organ. ' discharge oscillators simultaneously to an output While the invention is hereinafter described in circuit without affecting the individual oscillation connection with a musical instrument, it will be electrical oscillations, a plurality of glow dis charge oscillator circuits. understood that the invention contemplates pro frequency of the separate glow discharge oscil lators. I have provided a photo-electric system which will be responsive to the glow or ?uctuat tion of electrical oscillations as obtained from one ing light emitted by the glow discharge tube of or more glow discharge oscillators which may be capable of general application. 20 the oscillator circuit. The light from the glow discharge tube ?uctuates at the exact frequency It is well known that a glow discharge oscillator of the oscillating circuit. By optically coupling may be employed to produce electrical oscillations the glow discharge oscillator to the photo-electric ‘varying in frequency from less than 1 cycle per system and associated ampli?er for reproducing second to more than 30,000 cycles per second. It has been attempted to employ such a glow dis 25 the electrical signal into audible sound, I have provided a system whereby two or more glow charge oscillator to produce electrical oscillations discharge oscillators may be connected at the of audio frequencies capable of being used in a same time to the output without affecting the musical instrument. Great difliculty has been individual frequencies of the oscillator circuits. encountered‘, however, when attempting to use a This photo-electric system of coupling the glow plurality of glow discharge oscillators to produce discharge oscillators to an output circuit is very a complex audio oscillating signal, such as would economical to manufacture. be obtained when playing two or more notes It is, therefore, a further object of my inven simultaneously in the production of a harmonic tion to provide a method and apparatus of op passage. To produce a harmonicl'pa'ssage, it was tically coupling two or more glow discharge oscil necessary to electrically connect two or more lators to a photo-electric reproducing circuit for oscillator circuits to an output ampli?er and translating the oscillation frequencies generated speaker. The di?iculty encountered was appar in the oscillator circuits to audible frequencies. ently due to the fact that the electrical coupling viding a method and apparatus for the produc It is a further object of my invention to provide oscillators would usually cause the oscillators to 40 a method of producing a complex electrical os cillation resulting from the effect of a simul tie in ‘together and behave as a single oscillator. tanecus exposure of two or more fluctuating light That is to say, the individual frequencies of the or connection between two or more glow discharge individual glow discharge oscillators, when elec trically coupled together, would be degenerated sources as obtained from two or more glow dis charge oscillators upon a photo-electric reproduc to a single new‘frequency and would not be a, 4-5 ing system. It ‘is still a further object of my invention to complex frequency resulting from the simultane provide a musical instrument employing the ously superposi'ng of the two individual frequen optical system of coupling the glow discharge cies upon each other. Therefore, it'was apparent oscillators to the photo-electric reproducing sys that two or more glow discharge oscillators could tem having means associated with a key board not be electrically coupled together at the same for selectively exposing each of the glow dis time to produce a harmonic passage because of the fact that the speci?c frequencies of the indi charge oscillators to' the photo-electric reproduc vidual oscillators were changed. Attempts have‘ been’ made to overcome this ing system. It is another object of my invention to pro di?iculty‘ by employing separate oscillation or 55 vide' almusical instrument employing the optical 2,408,589 3 system of coupling the glow discharge oscillators to the photo-electric reproducing system having means associated with a key board for selective ly exposing each of the glow discharge oscillator tubes to the photo-electric element and so con structed that the amount of optical exposure of the glow discharge tube to the photo-electric element will be proportional to the amount of pressure applied to the clavier key of the key board, thus offering a means of varying the dy namics of the individual electrical signals and en abling the production of percussion effects, or the like. It is still a further object of my invention to provide a musical instrument employing the op tical system of coupling the glow discharge os cillators to the photo-electric reproducing system in which the glow discharge oscillator circuits are provided with a means for periodically raising and lowering the oscillation frequencies to thereby produce a vibrato effect. Further objects and advantages of my inven tion will be apparent by reference to the follow» ing speci?cation and drawings, in which: Figure 1 is a schematic diagram of a conven tional glow discharge oscillator using a neon glow tube; Figure 2 is a schematic diagram of a glow dis charge oscillator in association or optically cou— pled to a photo-electric reproducing system com-i prising a photo-electric cell and a photo-electric ampli?er of standard design; ‘ Figure 3 is a schematic diagram of a number of glow discharge oscillators provided with a con: mon source of applied voltage and showing a means for periodically raising and lowering the applied voltage to provide a tremolo or vibrato effect; Figure 4 is a diagrammatic showing of one form of apparatus for selectively exposing the glow 4 discharge tube of an oscillator circuit to a photo electric cell by means of an optical shutter in connection with a clavier key; Figure 5 is a schematic diagram showing a plu rality of glow discharge oscilators and diagram matically showing a single photo-voltaic type photo-electric element responsive to the glow of any of the glow discharge tubes in the circuit; Figure 6 is a cross-sectional view or the photo~ voltaic type cell diagrammatically shown in Fig ure 5; ‘ circuit. Therefore, the glow discharge oscillator circuit may be tuned to different oscillation fre quencies by varying the value of any of these constants, such as the capacity, resistance, and applied voltage. If the voltage is maintained constant, the condenser or resistor values may be varied to change the oscillation frequency. I have found, by experimentation, that the best practice for tuning the oscillator to desired fre~ - quencies is to adjust the values of the resistor 2 for the lower frequencies included in the range up to 1,000 cycles per second and to adjust the value of the condenser 4 for the higher frequen cies included in the range of 1,080 cycles per sec ond up to the highest frequency desired. In Figure 2 of the drawings, I have shown a schematic diagram for a glow discharge oscil lator that is optically coupled to a photo-electric reproducing system. The glow discharge tube 5 is connected in series with the resistor 6 and the applied voltage as obtained from the voltage di_ vider l. A condenser 8 is shunted in parallel with the resistance 6. By adjusting the resist ance 6 or the condenser 8 as described above in connection with Figure l, the frequency of 0*‘ cillation in the oscillator circuit may be changed. It is a function of the glow discharge oscillator tube 5 that the light or glow emitted by the tube when oscillating in an oscillating circuit will ?uetuate at a frequency which is identical to the frequency of the oscillating circuit. Optically conected to the glow discharge tube 5 is a photo electric cell or other photo-electric responsive element 9. This photo-electric cell is provided with a suitable photo-electric ampli?er which I have shown in Figure 2 of the drawings to be of the resistance coupled type. Plate, grid, and bias resistors R, together with coupling and by-pass ' condensers C, triode tube Hi, and output trans former T, constitute a schematic showing of a standard type ‘of resistance coupled ampli?er. It should be understood that any other desired form of ampli?er, such as a transformer-coupled or a direct~coupled ampli?er, may be used in place of the resistance-coupled ampli?er which I Figure 7 is a diagrammatic showing of a modi ?ed form of key arrangement for selectively ex posing the glow discharge tube of an oscillator circuit to a photo-electric cell in which the de gree of exposure will be proportional to the amount of pressure on the key or the relative depressed position of the key; 4 age, cause the circuit to oscillate, and the fre quency of the oscillation may be varied by ad justing the constants of the circuit, such as the resistor 2 and the condenser 4. The frequency of the oscillation produced is aiTected by the capacity, resistance, and applied voltage in the ‘ Figure 8 is a diagrammatic showing of still another modi?ed form of key arrangement to i provide pressure responsive dynamic control of the individual tones produced; and Figure 9 is a front detail view of the optical shutters shown in Figure 8. Referring to the drawings, Figure 1 is a sche matic diagram of a conventional glow discharge oscillator circuit having a neon or other form of have shown. It will be apparent that any de sired number of photo-electric cells may be con nected to a single ampli?er. The operation‘of the electrical system shown in Figure 2 of the drawings and described above is as follows: When the oscillating circuit is ener gized, the glow discharge tube 5 will emit a ?uc tuating light corresponding in frequency to the frequency of the oscillating circuit in which the glow discharge tube is connected. The ?uctuat ing light emitted by the glow discharge tube 5 is directed upon the photo-electric element 9 and will cause the photo-electric element 9 to trans late the light impulses into a ?uctuating or os cillating current which will be coupled to the glow tube I connected in series with a resistance photo-electric circuit by the resistance-coupled preampli?er and transformed by the output 2 and a source of direct current, such as a bat transformer T to the proper impedance desired tery 3 or the like. A condenser 4 is placed in par~ allel with the resistor 2. A make and break switch S is shown to selectively energize the oscillator. As is well known, a glow discharge tube‘in connection with a circuit,‘such as described in Figure 1, will, when energized by an applied volt for a power ampli?er or the voice coil of a loud speaker (not shown). Thus, an electrical system is provided for coupling a glow discharge oscilla tor to a reproducing system in which the circuit for the glow discharge oscillator is electrically independent of the circuit for the reproducing caresses‘ r 0 system. With such an arrangement of optical coupling, it is possible to connect two. or more glow. discharge oscillators simultaneously to a photo-electric reproducing system, and. because 6 , tric reproducing ‘system; and speaker. In opera tion; the electrical. system for periodically rais ing and-‘lowering the applied voltage to the oscil lator circuits is ‘as-follows: The; voltage of 350 the circuits of the oscillators and the circuit of. the reproducing system are independent, there will be no electricalcoupling or connection between the. individual‘ oscillator circuits, and the di?i volts appliedacross the voltage divider D which culties previously encountered, where electrical drawings andis not electrically contacting the is comprised of. the resistance segments ll, l2, l3, andv I4. When the vibrating switch blade I8 is in the mid-position shown in Figure 3 of the coupling or connection between the oscillators 10 switch contactsl?sor H; the applied voltage sup plied to the line H51 in the glow discharge oscilla was used,.are avoided. Figure 3 of the drawings shows a plurality of tors is obtained from the voltage divider D at the point‘ between. resistance segments l2 and I3. glow. discharge oscillators provided with a com The oscillators will then be supplied with a nor mon source of applied voltage. The appliedvolt mal amount of applied voltage. When the vi age for the circuit. shown in Figure 3 is, periodi callyvaried about a mid-point to obtain a period: brating switch blade I8 is electrically contacting ie rise and fall in the frequency of oscillations the switch contact I5, the resistance‘ 24 will be produced in the glow discharge oscillator cir placed in parallel with the resistance segment, l2, thus effectively reducing the total resistance of cuits. A voltage divider generally indicated by D. is divided into resistance segments ll, [2, l3, 20 the resistors I l and I2. and increasing the applied voltage to’the line l6 and the glow discharge oscil and M. An appliedvoltage of 350 volts is sup plied to the voltage divider D. At the point be lators. The frequency of the oscillators will then be raised above, the normal. When the vibrating tween the resistances. H and 12, the switch con switch blade I8 is in electrical contact with the tact I5 is connected, and at the point between the resistances l2 and IS, the glow discharge os cillators are connected by means of the line l6. switch contact [1, the resistance 24 will be con nected in parallel with the resistance l3, thus ef At. the point between resistances, l3 and M, the switch contact H is electrically connected. The switch blade l8is pivoted at, 19 and is connected fectively reducing the amount of resistances l3 by means of the pitman arm 20 to a crank 2| on the shaft ofv a small electric. motor 22,. The small lines Hiv and 25 of the applied voltage for the glow discharge oscillators, the applied voltagev to the electric motor is preferably of the synchronous type which will run at constantspeed, or. it may, if desired, .be providedwith suitable means to vary line 16 and the oscillators will be reduced. There fore, the frequency of the oscillators will then be lowered below the normal. Thus, it will be seen the speed, and it will be apparentthattheswitch blade l9. willbe periodically connectedat regular that the vibrating switch blade 18, periodically contacting the switch contacts l5‘ and I1, will intervals with the switch contacts l5. and I‘! when the electric motor is inoperation. Theswitch blade I8 is electrically connectedthrough an on or off switch 23. and resistor 24t0, the line l6 sup 40 cause the appliedvoltage to the line IIS and the glow discharge oscillators to be periodically raised plyingapplied voltage to. the glow discharge os cillator circuits. The glow discharge oscillator circuits which are connected to the common source ofapplied voltage, as supplied to the line I76 .and the ground connection 25, are provided witha number of glow discharge tubes 26,. It will benoted that. some of the glow discharge tubes. 26 are provided with variable resistances 21_ to adjust the. frequency of the oscillating circuit and thereby the frequency of the fluctuating light emitted by the discharge tube, while others of the glow discharge tubes are provided with variable. condensers 2B for adjusting the fre quency of. the oscillations and the ?uctuating light. As previously mentioned, the variable resistor. 21 is adjusted in the oscillating circuit when the oscillator is tobe tuned to lower fre quencies, whereas the variable condenser 28 is adjusted when tuning the oscillating circuit to and I4. As the resistances I3 and I4 are part of the voltage divider and are connected across the and lowered about a normal. When the switch blade i8 is in the position shown in Figure 3 and not contacting the electrical contacts 15 and I1, the applied voltage will be at a midpoint because of the fact that the resistance 24 is not electrical ly connected-into the circuit. It is important that the applied voltage common to all of the oscilla tor circuits be varied above and below a normal or mid-point as this prevents the illusion of the musical instrument'going out of tune when the vibrato is turned on or oif. A fixed condenser 29 is shown across the output of the voltage varying device to eliminate any undesirable oscillations in the glow discharge oscillators, due to the sparking of the switch contacts I5 and H with the vibrat ing switch blade l8. In Figure 4, I have diagrammatically shown oneform of apparatus for selectively exposing the ?uctuating light from the glow tubes to a photo electric element. Mounted within the lightproof box 30 is the photo-electric cell 31 and neon higher frequencies. 60 glow tube or its equivalent 32. The condenser As the oscillation frequency of the glow dis. 33, and resistor 34 for the glow discharge oscil lator circuit are also mounted within the light charge oscillator is a function of the resistance capacity and applied voltage, it will be apparent proof box. A thimble 35 encloses the glow tube that varying the applied voltage will vary the 32 and is provided with an aperture or window 36. Positioned'in front of the window 36 is a frequency of oscillations. As shown in Figure 3, shutter element 31 pivoted on the spring arm 38 a plurality of glow discharge oscillators are pro bolted to the lightproof box at 39. A connecting vided with a common source of applied voltage. rod in is connected to the spring arm 38 of the An electrical system is also shown in Figure 3 shutter 31 and passes through the lightproof box and described above for periodically raising and to connect with the'clavier key 4| mounted upon lowering the applied voltage about a mid-point, 70 the spring arm 42. When the clavier key 4| is so asto periodically raise and lower the oscilla depressed, as shown in the dotted lines, the shut tion frequencies of the oscillator circuits, and ter 31 will be removed from in front of the window thereby produce a vibrato effect which will be au 36, allowing the ?uctuating light from the glow dible when the fluctuating light from the glow discharge tubes is interpretediby the1-photoeelec-v 75 discharge tube 3.2 toimpinge upon the elements 2,408,589 7 of the photo-electric cell 3|. With this form of apparatus, it is possible to maintain the glow discharge oscillators in operation at all times. Whenever it is desired to optically couple a glow discharge oscillation circuit to the photo-electric reproducing system, the clavier key is depressed, thus removing the shutter from in front of the aperture and permitting the ?uctuating light from the glow discharge tube to affect the photo electric element. Any number of lightproof boxes containing the photo-electric tube, together with the glow discharge tube and shutter, may be pro vided and simultaneously operated, if desired, without affecting the individual oscillation fre quencies of the individual glow discharge oscil lators, since the electrical circuits for the photo electric reproducing system and the glow dis charge oscillators are independent of one an other. In Figure 5 of the drawings, I have shown a number of glow discharge oscillator circuits pro vided with glOW tubes 43 and supplied with a com mon source of applied voltage of 350 volts. Var iable resistors 44 and variable condensers 45 are used to adjust the frequency of the ?uctuating light given oil by each of the glow discharge tubes 43. A photo-voltaic type of photo-electric ele ment 46 is provided to receive the ?uctuating light of the glow tubes 43. The photo-voltaic type of photo-electric cell is an elongated tube which can be made of sufiicient length to simul taneously respond to a large number of glow dis charge tubes. If the glow discharge oscillator circuits and tubes are to be used in the construc 8 lation or tone produced in response to a greater pressure applied to depress the clavier key. Referring to Figure 7, a clavier key 52 mounted upon the spring arm 53 is connected by the con necting rod 54 to the shutter 55 pivoted on the spring arm 53. A thimble 5i encloses the glow discharge tube 58 and has an aperture 59 through which the light from the glow discharge tube may pass to the photo-electric cell 69. When the clavier key 52 is depressed the shutter 55 will be removed from in front of the aperture 59, thus eyposing the glow discharge tube 58 to the photo electric cell 60. It will be apparent that the amount of exposure or uncovering of the aper ture 59 will be proportional to the pressure ap plied to depress the clavier key 52. To indicate the relative depressed position of the clavier key 52, I have provided stops El, 62, and 63 cooperat ing, respectively, with springs 54, 65, and 66. If the key 52 is depressed slightly, stop 6i will con tact spring 64, thus giving an indication of the position of the key 52 and the relative exposure of the aperture 59. If greater pressure is applied to depress the key 52 the stop 62 will engage spring 65, thus giving a further indication of the position of the clavier key and the relative ex posure of the aperture 59. A rest 57 is provided to indicate to the player when the clavier key has been depressed all of the way to completely expose the aperture 59, thus giving the greatest dynamic volume to the electrical oscillation re produced through the photo-electric system. By skillfully playing, it is possible, with the form of my invention just described above, to ac tion of a musical instrument, such as an electric 35 cent the individual notes in a passage to any de organ, it will be necessary to have at least ninety six glow discharge tubes and associated oscillator circuits. These glow disharge tubes may be placed gree desired, producing various musical effects, such as percussion or pizzicato effects. Referring to Figures 8 and 9, a slightly modi in a line within the cabinet of the musical in ?ed key arrangement is shown for the application strument, and the elongated photo-voltaic type 40 of my invention to an instrument primarily de of photo-electric cell may be optically aligned signed for producing percussion effects by pro with the line of glow discharge tubes. If de— portionally exposing the glow discharge tube to sired, however, more than one photo-voltaic type the photo-electric cell in response to the pres of photo-electric cells may be used to take care of sure applied to the key. The clavier key 68 is all of the oscillator circuits and glow discharge pivoted at 69 and is provided with a stepped ar tubes necessary to produce the ordinary range of rangement of stop positions 10, ll, and ‘i2. musical notes on a keyboard instrument. Springs l3’, ‘l4, and 15 are adapted to cooperate, A cross-section of the photo-voltaic type of respectively, with the stop positions ‘Iii, ‘II, and photo-electric cell is shown in Figure 6. An elon 12. A rest 11 is provided for indicating the fully gated casing 41 is provided with a glass window depressed position of the key 68. A shutter ele 48. Positioned within the casing is a surface of ment ‘[8 having an aperture or window 19 is slid light-sensitive substance 49 deposited on a metal ably positioned for vertical movement within the plate 59. An electrical contact or binding post light proof box 80 and in front of the aperture 5| is connected to the metal plate 50, while an or window 8| of the thimble 82 enclosing the other electrical contact or binding post (not . glow discharge tube 83. A detailed front view of shown) is connected to the light-sensitive sur the shutter element 18 is shown in Figure 9 of the drawings. A weight 84 is positioned at the face 49. The electrical.,contacts of the photo top of the shutter element 18. When the key voltaic type of photo-electric cell are connected 68 is struck the lever end 85 of the key will in the usual manner to a suitable ampli?er. In Figures 7, 8, and 9 of the drawings I have 60 cooperate with the bottom end of the shutter element 18 to thrust said element upward, and shown two modi?ed forms of keying arrange the intensity of the impact will determine the up ments for selectively exposing the light of a glow ward distance which the shutter 78 is moved. If discharge tube to a, photo-electric element. The the key 68 is struck sharply the shutter element use of an optical keying system such as my inven 65 18 will be thrust upward to its full extent, thus tion employs offers a means for varying the dy completely exposing the glow discharge tube to namic volume of the individual electrical oscil the photo-electric cell. When the key is fully lations produced by the photo-electric reproduc depressed, as shown by the dotted lines A’, the ing system in accordance with the manner in shutter element 18 will be moved so that the which the keys are struck. That is to say, I am 70 center line C of the aperture 19 will be in the enabled to proportionally expose the glow dis position shown at A to completely register the charge tube to the photo-electric element in ac shutter 19 with the window or aperture 8| of the cordance with the pressure applied and the posi thimble 82. If the key 68 is depressed to the posi tion of the manually depressible key to thus give tion shown in dotted lines at B the center line of a greater dynamic volume to the electrical oscil 75 the aperture 19 will be in the position shown at 1 2,408,589 10 9 the clavier key M to thus selectively energize the desired glow tube and oscillator circuit to cause the glow tube to emit the desired frequency of fluctuating light for a?ecting the photo-electric B, thus partially exposing the light of the glow tube to the photo-electric element. By skillfully playing with this arrangement the key 68 may be struck sharply to- momentarily completely ex pose the‘ glow discharge tube, but due to the reproducing system. It is to be understood that the system shown and described is merely an illustration of the pre ferred embodiment, and that such changes may be made as fall Within the purview of one skilled in the art without departing from the spirit of the invention and the scope of the appended weight 84 and as soon as the momentum of the shutter element v‘I8 is overcome the shutter will fall to again shield the light of the glow discharge tube from the photo-electric cell, thus producing a percussion tone of great initial dynamic volume, but decaying to a tone of low volume or of no volume at all. If the player desires, the key 68 may be struck sharply to the position shown in the dotted lines at A’, and then be released to the position shown in dotted lines at B’, thus claims. I claim: 1. A light sensitive system comprising a plurality of glow discharge tubes, oscillating circuits con tinuingly energizing said tubes, means for tuning momentarily completely exposing the glow dis charge tube, but subsequently allowing the glow discharge tube to be but partially exposed. This each of said circuits to a certain frequency, elec tric means outside of said oscillating circuits adapted to respond to the ?uctuating light is of great importance when the player desires to cause the volume of the tone to be of great initial 20 emitted by said tubes, means normally shielding intensity but to decay gradually to a lower volume said photo-electric means from said light, selec level and thus prevent an abrupt ending of the tively operable means whereby said shielding tone. means is rendered ineffective as regards the light I have described above a system for produc emitted by one or more of said tubes so that said ing electrical oscillations in which a plurality of photo-electric means is correspondingly activated, glow discharge oscillator circuits may be used. and an ampli?er fed by said photo-electric means. By optically coupling the individual glow dis 2. A light sensitive system comprising a plurality charge oscillator circuits to the reproducing sys of glow discharge tubes, oscillating circuits con tem, I am enabled to couple two or more of the tinuingly energizing said tubes, means for tuning individual oscillator circuits to a single repro each of said circuits to a certain frequency, photo ducing system without electrically vconnecting the electric means outside of said oscillating circuits individual oscillator circuits to each other. The adapted to respond to the ?uctuating light ?uctuating light emitted by the glow discharge emitted by said tubes, a movable shutter associ tube of the glow discharge oscillator will fluctu ated with each of said tubes normally shielding ate at the exact frequency of the oscillation in 35 said photo-electric means from said light, means the oscillating circuit, and as the photo-electric for selectively moving said shutters to permit ac element is responsive to this ?uctuating light, the tivation of said photo-electric means by the light electrical signal generated in the photo-electric emitted by one or more of said tubes, and an am cell will be identical in frequency to the frequency pli?er fed by said photo-electric means, of the oscillating circuit. .40 3. A light sensitive system comprising a plurality While I have described above, in connection of glow discharge tubes, oscillating circuits with Figures 4 and 7 through 9 of the drawings, adapted to continuingly energize said tubes, a mechanical methods of selectively exposing a common normal voltage supply for said circuits, glow discharge oscillator to a photo-electric re producing system, it should be understood that ‘ other means of selectively coupling the oscillator circuits to the reproducing system may be em ployed. Instead of maintaining the discharge tube and oscillator circuit energized at all times and using an optical shutter to control the cou means for tuning each of said circuits to a certain normal frequency, a photo-electric system inde_ pendent of said circuits disposed for energization by light emitted by said tubes, means for se lectively controlling such light emission, an am pli?er fed by said system and means for rapidly 50 cyclically varying the voltage supply between pling of the glow discharge tube to the photo above and below normal whereby to cause corre electric cell, I may provide a switch, such as is shown in Figure 1 of the drawings, in series with sponding variations in the frequency of said tubes the glow tube and its oscillator circuit. This switch S, shown in Figure 1, may be connected to 55 and thus produce a vibrato effect. ALVIN w. WELLS.