Патент USA US2096756код для вставки
Oct. 26, 1937. . E. S. PURINGTON 2,096,756 DYNAMIC MULTIPLIER Filed June 25, 1935 m l m“ LVVQENTORH EHison S. Pufing'l'on. ATTORNEY ‘2,096,756 Patented Oct. 26, 1937 UNITED » STATES ' PATENT OFFICE 2,096,756 DYNAMIC MULTIPLIER Ellison S. Purington,,Gloucester, Massnassignor to John Hays Hammond, Jr., Gloucester, Mass. Application June 25, 1935, Serial No. 28,230 18 Claims. '(Cl. 179-1001) and for records requiring rapid expansion at low This invention relates to sound reproducing systems, and more particularly to an improved system for automatically expanding or multiply ing the dynamic range of sound energy. The in volume. The invention also provides tone control means ' to discriminate against the higherfrequencies, 5 vention provides more speci?cally for obtaining particularly when the volume control is set for the desired dynamic expansion or multiplication - high input values. Manual adjusting means may be included to effect the necessary control for in a single stage of‘ ampli?cation. . . ' In one embodiment tubes having a plurality of diiierent records. ' control elements are used to produce the desired 10 dynamic range in a single stage of ampli?cation without critical adjustments. The tubes may be of the triple grid type in which case the dynamic . control is preferably applied to the ?rst or con trol grid and the'third or suppressor grid, the 15 plate voltage and second or screen grid’ voltage being ?xed at their normal rated values with respect to the cathodes. In the absence of sig nals, the control grid may be biased to, for ex ample, about —‘7 to —10 volts, and thesuppressor 20 grid may have a potential of from -,-30 to —40 volts. With increase of signal the negative bias - on these grids is decreased as an increasing func tion of the signal strength up to a predetermined maximum bythe action of a control circuit. vThe 25 control circuit may comprise an auxiliary ampli ?er tube of the duplex-diode triode type (com mercial type 55, for example) feeding a network including a pair of recti?ers and resistances so as to build up a voltage drop across the resistances proportional to the signal strength. The resist ances are connected in circuit respectively with the control grids and the ‘suppressor grids of the main ampli?er so that the voltage drop therein opposes the normal negative‘bias of said grids. The diodes of the auxiliary ampli?ef tube may be used to limit the voltage drop across the resist ances to a predetermined value so as to prevent the biasing potential on the control .and sup pressor grids from dropping to a value such that 40 distortion would result. ' By applying control to the two sets of grids it is possible to obtain sufficient control in one stage of ampli?cation without necessitating critical ad The invention also consists in the various new and original features of construction and com 10 binations of parts hereinafter set forth and claimed. Although the'novel features which are believed to be characteristic of this invention will be par ticularly pointed out in the claims appended here 15 to, the invention itself, as to its objects and ad vantages, the mode of its operation and the man- ‘ ner of its organization may be better understood by referring to the following description taken in \ connection with the accompanying drawing form-' 20 ing. a part thereof, in which: The ?gure‘illustrates diagrammatically the sys tem as applied to the reproduction of sound from the sound record of a talking moving picture pro jector and phonograph. ' . ' In the following description and in the claims, various parts will be identi?ed by speci?c names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit._ Referring to the acompanying drawing more in ‘ detail, a phonograph pick up “I is shown which is connected to two contacts ofa double-pole. double-throw switch H, the other contacts of which are connected through a transformer I2 35 to a photoelectric cell 13. Light from a lamp- “! ' is focused, by means of a lens l5, through an aperture HS in an aperture plate ll, upon the sound record of a moving photographic ?lm 18. The light which passesthrough this ?lm then im pinges on .the photoelectric cell l3. _ The blades of the switch II are! connected through a transformer 20 to the input circuit of > justments of the initial bias settings. By using l a space discharge ampli?er 2|. Connected across this input circuit is a tone control ?lter compris 45 45 for the main ampli?er a type of triple grid tube with remote cut off on-the control grid (com ' mercial type 58, for example) the control on ing parallel branches, one containing‘a resist ance 22 and a condenser 23 in series, and the this grid will be smooth and uniform, determining other containing a resistance 25. This tone- con,-v trol ?lter is a compensating device adapted to the dynamic range of the ampli?er, while the con‘ trolon the suppressor grid may be made abrupt . compensate for the undercutting of the bass tones 50 so as to suppress noise, for example, in periods-of in a sound record. The ?lter emphasizes the bass small or zero signal strength. However, the abrupt- cut off type of triple grid tube (com mercial type-57) 'may be also used to advantage in some instances, especially for. sound on ?lm tones by loading the transformer 20 more for high frequencies than forlow frequencies. It is to- be noted that this ?lter can be omitted provided a compensated pickup or transformer is employed. 55 2 2,096,756 ‘It is useful, however, when a transformer or pick up having ?at characteristics is employed and its value, will depend upon the transmission characteristics of the transformer or pick-up and the characteristics of the record which is to be com pensated. The output circuit; of the ampli?er 2| tentiometer 58. These elements may be adjusted _ to effect the desired frequency transmission characteristics or, in the event that the trans former 43 isdesigned to produce the desired ? delity, these elements may be omitted. . The tubes of the power‘ ampli?er 44 ar - includes a scratch ?lter 26 and two potentiom vpreferably of the triple grid vtype. having a cathode 5|, control grids 52, screen grids 53, eters 21 and 28 in series. The scratch ?lter 23 is used to cut out excessive high tones, such for ex.-_ and suppressor grids 54. The control grids 52 may be connected to the secondary of the trans 10 ample as all tones above a frequency of 6000 cycles and may be of any well known design adapted to former 43. produce the desired characteristics. The ampli-» grids 54 may be grounded and the screen grids ?er 2| is supplied with plate power from a tap 29 on a battery assembly 38. The potentiometer 15. 21 is connected to a tone circuit 24 comprising a The cathodes‘ 5| and suppressor 53 may be connected to, the tap 29 on the'bat tery assembly 38; A tone '?lter comprising‘ parallel branches, one containing a resistance 58 15 high pass ?lter network adapted to shunt more and a condenser 59 in series, and the other ‘con of the high frequencies than the low frequencies, taining two condensers 68, may be connected the effect being determined by the podtion of the across the output circuit of the power ampli?er movable contact of the potentiometer-11. When 44. This tone ?lter ‘is designed to dampen out 20 this contact is raised (as viewed in the drawing) ' resonant frequencies which are occasionedv by a greater proportion of the higher frequencies are the mechanical vibrating elements. The char shunted and vice versa. The potentiometers 31 ‘ ,acteristics depend upon the resonance character and 28 provide a constant impedance output for istics of the speaker. Compensation for the me the ampli?er 2| ‘while permitting adjustment of chanical resonance of the speaker may also be 25 the energy fed to the next stage of ampli?cation ' effected in other well knownways in which case the tone ?lter will be modi?ed accordinglyor and to the tone circuit. _ The potentiometer 28 is connected through a may be omitted in certain instances. The ?eld transformer 3| to the input circuit of a push-pull coil 8| of the loud speaker 46 may be connected ampli?er 32 comprising two tubes 33 having a between the tap 29 and a tap 82 on the battery assembly 38. > ' 30 plurality of control elements, such for example as triple grid tubes of the type known com Connected across the output circuit of the mercially as 57 or 58, and having cathode 34, ampli?er 2| by a coupling ‘resistance 85 is a control grids 35, screen grids 36 and suppressor . branch ampli?er recti?er system including a grids 31. The secondary of the transformer 3| duplex-diode triode tube 88, which may be of may be connected to the control grids 33 and commercial type 55, for example, andmay have the cathodes 34 may be grounded. The screen a cathode 81, a grid 88, an anode 89 and a pair of grids 36 may be connected to a tap 38 on a re diodes ‘I8 and 1|. The grid bias is applied to the sistor 39, which is connected between the tap , tube 86 from a tap‘ ‘I2 on a. control resistor as 29 on the battery assembly 38 and ground. ‘ ' sembly 13, which is connected between the nega The output circuit of the ampli?er 32 is con tive terminal of the battery 38 and ground. The 40 nected'through a transformer 43 to the input cathode potential of the tube 83 is determined circuit of a push-pull power ampli?er 44, the by a tap 14 on a second -_resistor assembly 15, output circuit of which is connected through a which is in parallel with the resistor assembly transformer“ to the, moving coil of a loud _ 13 and is designed to carry heavy currents. ‘The plate 69 of the tube 68 may be connected through ‘speaker 46. . ' A resistance 41 may be connected across the the primary of a transformer 18 and a resistance primary of the transformer 43 to maintain the 98 to the tap 29 of the battery 38. frequency characteristics substantially inde The control grids 35 of the tubes 33 are con pendent of the gain ratio characteristics. This nected through a resistance 88 and a resistance resistance 41 has a value such that the combined 8|, to an adjustable contact 82 on the resistor impedance of this resistance and the internal assembly 13. The suppressor grids 31 are con output impedance of the tubes 33 in parallel nected through a resistance 83 to an adjustable approximates the impedance for which the contact 84 of the resistor assembly 13. The re transformer 43- is designed to effect uniform sistance 8|, being-in the output circuit of the tube 86, should have a value somewhat greater 55 transmission on all frequencies within the de sired range. If the transformer 43 is designed to 7' than the internal output impedance of said tube operate across an input impedance correspond in order to operate most effectively therewith ing to the internal outputimpedance of the and may be varied in accordance with the design tubes 33 this resistance 41 can be omitted. of the tube 66 to‘ produce the most effective to The tubes 33 may be supplied with plate power ' results. The resistance 88 is high as compared from the tap 29 on the battery assembly 38. to the resistance 8| so that the parallel circuit A ?lter network comprising parallel branches, including the resistance 88 and the condenser I88 one containing a resistance 48 and the other con‘ will not interfere with the operation of the re taining a condenser 49 and potentiometer 58 in' sistance 8|. It should not be sufficiently high, series, may be connected across the secondary of however, to introduce excessive resistance in the the transformer 43 for ‘tone control purposes. grid return circuit in which it is connected. The The resistance 48 is of a value adapted to cor resistance 83 has a valueaof the order of the root for the lack of ?delity of the transformer rated secondary output impedance of the trans 43 and may be omitted provided the transformer former 18 across which it is connected through , 70 is designed to operate satisfactorily without the the recti?er tube 96 to be described. The output circuit of the auxiliary ampli?er same. The condenser 49 and potentiometer 58 are used for tone control purposes and provide a tube 86 comprises parallel branches, one includ partial shunt for the high frequencies, the ing a stopping condenser 88,'a resistance 89 and characteristics of which depend upon the value the resistance 8|, the other including the pri 75 of the condenser 49 and the setting of the po- , mary of the transformer". The condenser 88 20 25 30 40 so 60 ‘ 65 70 3 2,096,756,v is used as a blocking condenser. The resistance 7 89 together with the resistance 80 and the con denser 88 determines in part. the frequency re sponse characteristics of the control circuit. A recti?er 9| having acathode 92 and anode 93 is connected. across the resistance 8| in such manner that current passes through the resist ance 8| only in the direction of the arrow, whereby the potential drop in the resistance 8| 10 opposes the. normal negative bias on the grids 35 derived from the tap 82; The recti?er 9| may comprise a three element tube having a grid 94 connected to the anode 93. J ‘ i . The secondarycircuit. of the‘ transformer 16 15 may include a recti?er 96 and the resistance 83 in series, the recti?er 96 being adapted'to pass current through the resistance 83 only in the di more resistance is put in parallel with the tone circuit 24 thus causing more and more of the high frequency tones to be shunted and. decreas ing the proportion of high frequency supplied to the ampli?er 32. - ' Energy is fed from the potentiometer 28 to the input circuit of the push-pull ampli?er 32 the amount being determined by the setting of the potentiometer 28. This energy is ampli?ed‘ by the ampli?er 32 and is fed through the trans 10 former 43 to the push-pull power ampli?er 4,4 where it is‘ further ampli?ed. The output of the ampli?er 44 is then fed through the transformer 45 to the loud speaker .46 where it is reproduced 15 as speech or music in a well known manner. Some of the energy ‘from the output circuit of the ampli?er 2| passes to the branch ampli?er rection of the arrow so' that the voltage drop in _ recti?er system where it is ampli?ed by the auxi " said resistance opposes'the normal negative grid iliary ampli?er 66 and is fed to the resistance 8| and to the transformer ‘16. A portion of'the 20 20 bias applied to the suppressor grids 31 from the contact 84. -The recti?er 96 may also comprise a three element tube having a grid 91 connected to its anode 98. ' The diodes 10 and 1| of the ampli?ertube 66 energy thus passes through the stoppage con denser 88, resistances 89 and 8| and recti?er 9|, ' causing a ?ow of unidirectional pulsating cur rent, through the resistance 8| in the direction of the arrow, thereby building up a pulsating po 25 25 may be used to limit the voltage drop in the re sistances 8| and 83 respectively. For this pur ' tential di?’erence across this resistance, which pose they are connected to the positive ends of ?uctuates in accordance with the envelope of said resistances. The diode ‘10, for example, may the signal strength impressed on resistor .65, and opposes the negative potential which is normally be connected through the resistance 80 to the imposed upon the'control grids of the ampli?er 30 30 positive end of the resistance 8|, and. the diode 1| may be connected to the positive end of the‘ 32 from the contact 82 of the resistor assembly resistance 83. When the potential dropacross 13. The potential thus produced across the re-' said resistances becomes such that the diodes I sistance 8| automatically increases the gain ra become positive with respect to the cathode 61 tio of the. ampli?er 32 with increase'of signal 35 and vice versa. The rate of increase or as of the tube 66 space current will ?ow between - strength the cathode‘ and the diodes and further increase decrease of the gain ratio or the time constant of the circuit is determined by the value of the in potential drop across said resistances is pre condenser I00 and resistance 80- which may be vented. Condensers I00 and |0| may be con nected between the diodes 10 and 1| and ground selected in accordance with the effect desired. The potential drop across the resistance 8| is 40 40 to control the timing of the control circuit. The limited by theaction of the diode 10, which pre condenser. I00, in connection with the resistance vents this potential from increasing beyond a 80, controls the time constant of the control cir- ' cuit and is chosen to produce the desired effect of the crescendo and decrescendo of the repro-v 45 duced signal. The condenser |0| serves a simi lar function in controlling the time constant of the suppressor grid. The condensers I00 and |0| may be designed to cause the signal grid and suppressor grid to operate at the same time con 50 stant although in certain instances it may be v desirable to select these elements so as to cause the signal and suppressor grids to operate at dif ferent time constants depending upon the effect desired. , A triple pole double throw switch I02 is ‘pro vided for controlling the dynamic operation of the circuit. When this switch is thrown up the two diodes 10 and 1| of the tube 68 are connected together andv to a tap I03 on the resistor as 60 sembly 13. When the‘switch I02 is open, these electrodes are independent of each other, and when the switch is thrown down the resistance 89 is short circuited. The cathodes of the vari - ous tubes may be heated in any well known man 65 ner, as by separate heaters supplied from a con venient source of current, not shown. _ In the operation‘ of ‘the form of the invention shown in the accompanying ?gure, the energy re ceived by the transformer 20 passes to the ampli 70 ?er 2| where it is ampli?ed and fed through the ?lter circuit 26, which eliminates the extremely high frequencies, to the potentiometers 21 and 28. vWhen the arm of the potentiometer 21 is in its lowest position the tone circuit 24 is short 75 circuited. As' this arm is ,moved up more and predetermined value, dependent upon the poten tial of the cathode 61 as determined by the posi tion of the tap 14 on the resistor assembly 15. 45 Any increase of potential above this amount will cause a. flow of current from ‘the diode 10 to the cathode 61, thus limiting the potential im- ‘ pressed on the grids 35 of the ampli?er tubes 33 to a value within the range of ef?cient operation 50 thereof. ‘ , The energy from the ampli?er 66 which passes through the transformer 16 is recti?ed by the recti?er 96 and ?ows through the resistance 83 in the direction of the arrow. This produces a, 55 potential difference across’ the resistance 83 which opposes the negative bias, normally im pressed on the suppressor grids 31 of the ampli ?er 32 from the contact 84 on theresistor assem 'bly 13. ‘In this way increase, of signal produces 60 a further increase in gainratio of the ampli?er 32. The time constant of this increase in gain ratio is ‘determined by the value of condenser |0| and the associated. circuits which may be selected to properly accentuate the change in gain ratio 65 produced by the control grid. ' The positive potential produced by the flow of I current through the resistance 83 is limited by. the action of the diode 1|, which prevents this poten tial from ' increasing beyond a predetermined O Value,-dependent uponthe potential of the oath ode 61 of the tube 66. In this way the potential ‘ impressed upon the suppressor grids of the am- - pli?er 32 is also limited by the action of the tube 66. 4 ‘ 75 2,096,756 With the switch [02 in the open position, as just described, expansion of a gradual nature is produced for high quality records, etc. If more abrupt expansion is desired, as for dance music and speech, the switch 102 is thrown down, thus short circuiting the resistance 89 which permits a greater amount of energy to be impressed upon the resistance 8|, thus increasing the speed of ,its action upon the ampli?er 32.v - 10' If non-dynamic or normal operation of the cir cuit is desired, the switch “I2 is thrown up, thus connecting bothvthe input circuit of the ampli-_ _?er 32 and the suppressor grids to the tap I03 on the resistor assembly 15 which eliminates the 15 action ‘of the resistances 8| and 83 and allows the circuit to operate substantially as a normal 'ampli?ea . I ' It will be understood that there may be inter linking of controls, as for example, control of 20 the low or initial bias settings of contacts 82 and -84 simultaneously with volume control of _poten tiometers 21 and 28 so as to provideless expan sion when the potentiometer is set for less volume and vice-versa. 25 - It will be noted that the above system pro vides for dynamic control on the control grid, and alsoon an additional control element of the tube. In this way, a great expansion is »made possible in a single stage of ampli?cation. The use ‘of a ' 30 duplex-diode triode ampli?er tube permits the . sary to an understanding of the present invention‘ and that the circuit may include the usual sources of potential, controls, etc. _ Although only a few of the various‘ _forms in which this invention may be embodied have been shown herein, it'isto be understood that the in vention is not limited to any speci?c construc tion, but might be embodied in various forms without departing from the spirit of the inven tion or the scope of the appended claims. 10 What is claimed is: ‘ 1. In a system for reproducing sound, an am pli?er comprising a_ space discharge tube hav ing a plurality of control electrodes connected to receive a biasing potential for controlling the 15 transmission characteristics of the tube a source of audio frequency sound energy, means to supply said audio frequency sound energy to one of said control electrodes, and means to vary the bias ing potential on said last control electrode and 20 also on an additional control electrode in accord ance with the envelope of the sound energy so that both control electrodes operate to vary the gain ratio of the tube as an increasing function of the sound energy whereby the additive control 25 effect of both control electrodes is utilized for ex panding the dynamic range of the reproduced signal. 2. In a system for reproducing sound, an am-l pli?er comprising a pair of space discharge tubes 30 connected in push-pull relationship, said tubes each having a plurality of control electrodes the limiting action to be obtained with a'minimum number of tubes. Obviously, this could be done in the ampli?er 2| instead of in the ampli?er 66, if ' corresponding control electrodes of the two tubes being connected by a common return to a source desired. 35 -The rectifying system embodies one possible of biasing potential'for controlling the trans arrangement .in which two types of recti?cation mission characteristics of the tube, a source of are utilized; one in ‘which the load is in series with the recti?er and the other in which‘ the out audio frequency sound energy, means to supply said audio frequency sound energy to one of said put voltage is developed in a resistor across the ‘ control electrodes of each tube and means to vary > the biasing potential on said last control electrode 40 'The tone. control circuits used in connection and also on an additional control electrode of with the various ampli?ers and the constant im~ each tube, in accordance with the envelope of the pedance output of the ampli?er 2| prevent tone sound energy so that both control electrodes distortion in the system. It is to be understood operatev to vary the gainv ratio of the tube as an increasing function of the sound energy whereby 45 45 that the various ?lters referred to above may be selected in accordance with standard ?lter de » the additive control effect of both control elec sign and are determined by the characteristics of trodes is utilized for expanding the .dynamic range of the reproduced signal. _ the cooperating elements of the circuit. For ex 3. In a. system for reproducing sound, an ampli ample, the ?lter requirements depend upon the ?er comprising a space discharge tube having a 50 50 mechanical and electrical characteristics‘of the record, the pickup and the reproducing device plurality of control electrodes connected to re ceive a biasing potential for controlling the trans and upon the transmission characteristics of the mission characteristics of the tube, a source of various tran'sformersand intertube coupling de , vices. It is to be understood that these devices audio frequency sound energy, means to supply 55 are shown diagrammatically in their simplest said _audio frequency sound energy to one of form and that they may be constructed in ac said control electrodes, means to vary the biasing cordance with the usual‘ practice. The value of potential on said last control electrode and also the various resistances and impedances which on an additional control electrode, in accordance are used for control purposes will depend upon with the envelope of the sound energy so that the characteristics of the particular ‘tubes with both control electrodes operate to vary the gain which they are to operate and will be determined -ratio of the tube as an increasing function of the 'sound'energy whereby the additive control in accordance with the known internal output im pedance of such tubes so as to produce the most e?ect of both control electrodes is utilized _for ex panding the dynamic range of the reproduced desirable results. The timing of the control-cir 65 cuits is a matter of choice depending upon the signal, and means to limit the change in biasing 65 results desired and thecharacteristics of theme potential on each control electrode so as to pre 0rd. Expansion of a gradual nature maybe‘ re vent signal distortion due to overloading. quired for high quality records, for example, 4. In a system for reproducing sound, an ampli whereas a more’ rapid expansion may be desired fier comprising a space discharge tube having a 70 for dance music or for records‘ having extreme plurality of control electrodes connected to re 70 volume ranges such as certain symphony records. ceive a biasing potential for controllingv the trans 40 recti?er. ' l . . A wide range of adjustment is possible by varying mission characteristics of the tube, a source of the different elements in the manner set forth above. It is also to be understood that only so audio frequency sound energy, means to supply said audio frequency sound energy to one of said 75 ‘much of the circuit has been set forth as is neces control electrodes, a control circuit including an 75 5 2,096,766 ampli?er, a resistor, means for rectional current through said tional to the output energy of ?er whereby a potential drop is across, and means applying said passing a unidi resistor propor-_ said last ampli change in biasing potential to a predetermined‘ value for preventing overloading of the tube. 9. In a system for reproducing sound, an ampli developed there potential drop to ?er having a control electrode connected to re ‘ oppose the normal biasing potential on a plurality of said control electrodes in said tube whereby the additive effect of both control electrodes is utilized to cause the gain ratio of said tube to 10 vary as an increasing function of the sound en ery for expanding thehdynamic range of the re produced signal; ' ,y ‘ v I‘ I 5. In a system for reproducing sound, an ampli ?er comprising a space discharge tubehaving a ceive audio frequency signal energy, a control cir cuit fed by the signal energy and connected to control the biasing potential on said control elec trode, said control circuit including-an ampli?er tube of the type having‘ a limiting electrode . therein and means connecting said limiting elec 10 trode to limit the control exercised by said con- ' ' trol circuit on said biasing potential. 10. In‘ a' system for reproducingsound, an audio ampli?er including a variable impedance device, '15 plurality ,of control electrodes, a source of audio - a source of audio frequency sound energy, a con frequency sound energy, means to supply said audio frequency sound energy to one of said con-' trol electrodes, a control circuit including an ampli?er, a pair of resistances, means for passing 20 a unidirectional current through said resistances proportional to the output energy of said last ampli?er whereby a potential drop is developed - thereacross, and means applying said potential drop to oppose the normal biasing potential on 25 a plurality of said control electrodes in each tube whereby the gain ratio of said ?rst ampli?er varies as an increasing function of said sound energy, and means to limit the potential drop, across said resistances to a value such that dis 30 tortion of the ampli?ed signal is prevented. trol circuit adapted to vary the impedance of said device as a function of the envelope of said < sound energy, said control circuit including a duplex ampli?er-limiter tube having a limiter electrode connected to limit the impedance varia tions produced by said control circuit. 20 11'. In a system for reproducing sound, an am- , pli?er comprising -a multiple grid tube, a source of audio frequency sound energy, means to im press said audio frequency sound energyon one 25 of said grids, a control circuit also fed by said audio frequency sound energy and adapted to V2 ry the bias on a plurality of said grids according to the'average signal strength, said control cir cuit including a duplex-diode-triode tube, the 30 6, In a system for reproducing sound, an ampli ' ,triode electrodes being connected to amplify the ?er comprising a space discharge tube having a energy in the control circuit, the diode electrodes plurality of control electrodes, a source of-audio being connected to limit the variation of bias frequency sound energy, means to supply said produced by the control circuit. 12. In a system of reproducing sound, a space 35 35 sound energy to one of said control electrodes, a control circuit including anampli?er tube of discharge ampli?er having two controlelectrodes the duplex-diode-triode type, means vsupplying energy proportionalto said sound energy to said in one tube connected to- a source of biasing po- _ tential, a control circuit. forcontrolling the gain _ ratio of said ampli?er, means for applying an audio frequency input signal to one of said elec 40 ?er means associated with said impedance means , trodes and to said control circuit,.said control triode, impedance means connected to receive en 40 ergy from the output circuit of said triode, recti to produce a potential drop thereacross propor circuit being adapted to vary the biasing poten tional to the average sound energy. means‘ tial to both of said control electrodes proportional whereby said potential drop opposes the normal to said input signal so that both control elec 45 bias on a plurality of said control electrodes, and "trodes operate to vary the gain ratio of said a limiter circuit including said diodes to limit ampli?er proportionally to ,the average value of the change in said bias.v ' _ '7. ‘A system for reproducing sound comprising a source of audio frequency sound energy, an am pli?er comprising a space discharge tube having a control grid and a suppressorhgrid, means sup plying said audio frequency sound energy to said control grid, means ‘to apply a biasing potential to both of said grids and means to vary said 55 biasing potential as a function of the envelope of said sound energy so that both the control grid and the suppressor grid operate to increase the gain ratio ‘of the tube with an increase in sound energy whereby the additive control effect of both grids is utilized for expanding the dynamic range of the reproduced signal. the input signal whereby the additive control e?‘ect'of both control electrodes is utilized for expanding the dynamic range of the reproduced signal. , , 50 ~ 13. A system for reproducing sound compris inga space discharge ampli?er having a plu- » rality of control electrodes for controlling, the gain ratio thereof, a source of audio frequency sound energy, a control’ circuit for varying the 55 biasing potential on both of said electrodes for increasing the gain ratio of the ampli?er as an increasing function of said sound, energy, a source of audio frequency sound energy, an means for applying said audio frequency sound energy to one of said electrodes and to said 60 control circuit and means associated with said control circuit for limiting its action on said control circuit so that overloading of the am ampli?er comprising a space discharge tube hav pli?er is prevented, 8. A system for reproducing sound comprising ing a control grid and a suppressor grid, means supplying said audio frequency sound energy to said control grid, means to apply a biasing po tential to both of said grids, means to vary'said biasing, potential as a function of the envelope of 70 said sound energy so that both the control grid and the suppressor grid operate to increase the gain ratio of the tube with an increase in sound energy whereby the additive control effect of both grids is utilized for expanding the dynamic range 75 ofithe' reproduced signal, and means to limit the . ' ‘ 14. A system for reproducing sound ‘compris 65 ing a space discharge ampli?er having‘ a plu rality’ of control electrodes for controlling the gain ratio thereof, a control circuit for varying said gain ratio comprising a second ampli?er, ‘a resistor connected in the output-circuit of, said 70 ampli?er and means controlled by said resistor for varying the biasing potentials on-the control electrodes of said'i?rst ampli?er in accordance with the average value of the input signal where by the additive control ,effect of both control 75 ,6" 2,098,756 electrodes is utilized for expanding the dynamic '17. In a system for reproducing sound com range of the reproduced signal. 15. A system for reproducing sound compris ing a single stage space discharge ampli?er hav ing a plurality of control electrodes i'orcontrol ling the gain ratio thereof, a control cir t for varying said gain ratio comprising a second am pli?er, a network including a resistor and recti ?er connected in the output circuit of said second prising a single stage space discharge ampli?er having av plurality of control electrodes for con trolling the gain ratio thereof, a control circuit having "an impedance, means for passing a current throughsaid impedance proportional‘ to the average value of the input signal and means responsive to the voltage drop in said impedance . for varying. the biasing potentials applied to 10 ampli?er and means controlled by said network ' the control electrodes oi said ampli?er whereby 10 the additive control e?'ect of both control elec trodes is utilized for expanding the dynamic range or the reproduced signal,v and means for limiting said action when loud signals are ap plied so that overloading is prevented. 15, 18. In the operation of an ampli?er circuit of the type including a space discharge tube having 16. In a system for reproducing sound com prising a single ‘stage space discharge ampli?er a plurality of grid elements one oi’ which is sup plied with audio frequency variations and having having a plurality of control electrodes for con means for establishing di?‘erent biasing poten 20 20 trolling the gain'ratio thereof, a control circuit having an impedance and means 'for passing a‘ tials upon the several elements, the method of for varying the potentials on the control elec trodes of said single stage ampli?er in accord ance with the average value of the input signal whereby the additive control e?ect 01' both con 15 trol electrodes is utilized for expanding the dy namic range oi’ the reproduced signal. current through said impedance proportional to the average value oi‘ the input signal and means 25 responsive to the voltage drop in said impedance for varying the biasing potentials applied to the control electrodes of said ampli?er whereby the additive control effect of both control elec trodes is‘ utilized for expanding the dynamic range of the reproduced signal. - controlling the ampli?cation which comprises simultaneously varying the biasing potentials of at least two of ‘said elements as an-increasing function of the strength of the 'signalsapplied to the input circuit 01' the'ampli?er. ELLISON s.‘ RURINGTCN.