US2426680A - Control for discharge devices - Google Patents

Description

P 2, 1947' G. E. GUSTAFSON 2,426,680

I CONTROL FOR DISCHARGE DEVICES Filed Jan. 13, 1944 ll V INVENTOR FIG 6 FIG. 1

FIG 2 =4 GILBERT E.GUSTAFS'ON HIS ATTORNEY Patented Sept. 2, 1947 CONTROL FOR DISCHARGE DEVICES Gilbert E. Gustafson, River Forest, 111., assignor to Zenith Radio Corporation, a corporation of Illinois Application January 13, 1944, Serial No. 518,071

7 Claims.

This invention relates to a high gain amplifier, and more particularly to a gain control for such an amplifier.

It is desirable to make portable radio and hearing aid apparatus of small size and with the least number of parts for the purposes of convenience in carrying and economy in manufacture, In such apparatus input signals must usually be amplified greatly and in controllable amount for accomplishing the purposes of the apparatus. The desirable qualities of smallness are better realized when the amplification of each stage is high and when the number of stages is a minimum.

It is therefore an object of this invention to provide a small high gain amplifier including an improved means for controlling the gain.

A further object of the present invention is to provide such a new and improved gain. control means in a regenerative high gain amplifier.

Still another object of the present invention is to provide a new and improved gain control, for a high gain regenerative amplifying stage, arranged to prevent oscillation of the amplifying stage.

The operating expense for replenishing batteries'in a hearing aid circuit is relatively large. In the mass production of hearing aids for universal use by persons having different degrees of deafness, it is desirable to take into account theiact that some people require greater voltage amplification in the hearing aid circuit than others. For purposes of economy, a person who requires a relatively small amount of amplification for satisfactor hearing should not be required to bear the relatively large operating expense of one who requires greater amplifica tion for satisfactory hearing. It is therefore another object of the present invention to provide a control in an electron discharge device not only for controlling the amount of gain in such device but also for controlling simultaneously the amount of space current flowing through the device such that relatively small space current flows when the gain is small, and, conversely, relatively large space current flows when the gain is large. 7

Yet another object of the present invention is to provide a new and improved gain control for a high gain regenerative amplifying stage in which such gain control serves also as a means for reducing the amount of current flowing to such amplifying stage.

The features of the present invention which are believed to be novel are set forth with par- (Cl. 179---17l) ticularity in. the appended claims. This invention itself, both asrto its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which: I I

Figure 1 shows. an improved hearing aid circuit incorporating a high gain amplifier circuit arranged in. accordance with the present invention;

and I Figs. 2 1107, inclusive, are modifications thereof.

In Fig. 1 there is illustrated an improvedhear ing aid circuit, incorporating a high'gain amplifier including electron discharge device iii and a second amplifier including electron discharge device M. The two amplifiers successively amplify signals from microphone H and impress such amplified signals on sound reproducing device I2 in linearly amplified form.

Sound waves impinging on microphone H are transformed into electrical variations in the main control electrode circuit of discharge device Hi. The microphone may, for example, be of the piezoelectric type as illustrated, or it may be of the magnetic type. The device 1!) greatly amplifies electrical variations produced by microphone H and the amplified electrical variations are further amplified by electron discharge device 14 before being applied to the sound reproducing device l2.

Microphone H, which produces electrical variations in response to sound Waves impinging thereon, is connected between the main. control grid I5 and the grounded filamentary cathode of discharge device 19; and a grid leak resistance It is co-nnected'in parallel circuit relationship with microphone IE. It is noted that substantially no grid current flows through resistance is since the grid !5 is at negative potential With respect to the cathode of device IE3, such negative bias potential being provided by connecting grid !5 through resistance 6 to the grounded negative terminal of source 43 having its terminals connected to opposite terminals of the cathode of device 10.

Electron discharge device E E3 is of the pentagrid type in commercial use andv may, for example, be of the type commonly known as the 135. The particular elements of this device Hi, however, are connected in a linear high gain amplifier circuit in a novel manner'not heretofore known. This invention is not limited to the use of a discharge device of the type commonly known as the 1R5, but within the scope of the. present invention amplifying discharge device I4.

any discharge device which performs equivalent functions is suitable. Large gain is realized when device I I3 is connected in the manner hereinafter I described and such large gain is substantially independent of the amplitude of a signal applied between the main control grid I5 and cathode of discharge device I0.

In general, device It! is connected so as to be effectively two amplifiers in cascade with regeneration between the two amplifiers. In addition to the main control grid I5, discharge device I'U' has what is termed a second control grid I8, a suppressor grid I9 connected to the cathode, a

main anode 25, and a pair ofscreen electrodes 2I and 22 on opposite sides ofthe second control grid I8.

Operating continuous potentials for device I are supplied from a voltage source 23 whose negative terminal is grounded and whose positive ter-' minal is connected to the main anode '20 of discharge device I through a series circuit including adjustable voltage dropping and gain control resistance 24 and output coupling resistance 25.

Electrodes 2| and 22 are connected together and are maintained positive with respect to the oathode'of device II! by connection to the positive terminal of voltage source 23 through the series aircuit including voltage dropping and gain'control resistance 24 and coupling resistance 26. The continuous operating potential of the second control grid I8 is stabilized by connecting it to ground and the cathode of discharge device I i through resistance 21.

When alternating currentsignals are impressed between the'main control grid I and cathode'of discharge device I0, substantially all of the alter-1 nating output voltage appears across the output '1 coupling resistance 25, a by-pass capacitance 28 of of, discharge device ID are impressed on the second control grid I8 through a coupling capacitance 29 connected 'therebetween'.

Therefore, alternating voltages applied directly to control grid I5 and indirectly to control grid IB cause alternating output signals to appear across resistance 25, which output signal are then, applied to the grid circuit of another linearly Coupling 'capacitance 31 and input resistance 32 are-connected in series and the series circuit formed thereby is connected in parallel circuit relationship to the'series circuit formed by output coupling resistance 25 and low reactance by-pass capacitance '28. Capacitance 3I is of relatively low reactance and serves essentially as a means for blocking the flow of continuous current from source 23 to resistance 32. The alternatingvoltage developed across resistance 32 through condenser 3I isapplied'between the grid and cathode of discharge device I4 so as to control the space current therein, which current normally flows due to the fact that voltage source 23"is connected between the plate and cathode of discharge device I4 through theprimary winding 34 of an output transformer 35.

Discharge device I4 is preferably ofthe pentode type having its suppressor grid connected to the voltagedropping resistance 36. The screen grid is maintained at constantpotential in the presence of signals of frequency corresponding to audio frequencies by means of low reactance bye pass capacitance 31, which is connected between the screen grid and cathode of device I4.

Alternating voltages developed across input resistance 32 are amplified linearly by discharge device I4, and appear across the secondary winding 39 of transformer 35 which is connected to impress those amplified voltages on the sound, reproducing device I2 which is connected across the terminals of secondary winding 39.

The filamentary cathodes of discharge devices wand I4 are preferably heated by current flowing therethrough as shown in Fig. 1. in such case the cathodes of discharge devices I0 and I4 are connected in parallel circuit relationship to voltage source 49. It is understood of course that, if desired, the filamentary cathodes of devices In and 64 may be connected in a series circuit with source 46 for heating purposes and for obtaining suitable-grid biasing potentials. I

The circuit thus far described is especially use,- ful as a hearing aid circuit and, because of the high gain obtained by the use of discharge device Ill, only two discharge devices requiring small space current are necessary for good performance. Because of the high gain obtained from the use of discharge device I5, a highly efiicient V and useful hearing aid circuit is provided which requires a small current drain from'voltage source 23. This is particularly truewhen, as in this instance, resistances 24,25 and'26are relatively large. thereto and features thereof, exclusive ,of the variable volume control resistance 24, are described and claimed in the copending application of John G. Prentiss, 'Se'rial N0; 504,958, filed October 4, 1943, and assigned to thesame assignee as the present application.

A feature of the present invention is that'ther volume of signals reproduced byrepro'ducing de-.

vice I2 may be controlled by adjusting volume 7 control resistance 24. An adjustment of resist' ance 24 causes no substantial nonlinearitybe-x tween the intensity of input signals applied to grid I5- and the intensity of signals developed across resistance 25 over a large range of input "signals; The magnitudeof resistance 24 not only-determines the gain in device I!) but controlsjalso the 1 amount of space current flowing in device -10.

Switch 45 having one of its terminals connected to the positive terminal of source 40 serves to energize and deenergize the cathodes of devices IIl'and I4.

Switch IE-having one of its terminals connected to the positive terminal of source 23 serves to in terrupt the space current flowing in devices I 0 and I4. Switches 45 and 4B-may be ganged together 7 operates as a pentode and includes control electrode i 8, screen electrode 22, suppressor electrode Ifiand anode 2i). 7 1

Measurements substantiate the theory that, in r 7 efiect, there are two amplifying stages in the V envelope of discharge ,device Ill: Withth'ed'e-= Device II], the circuit connections V The second, amplifyingstage vice adjusted for good operation, the gain realized from control electrode Hi to anode 20 was of such magnitude that, when multiplied b the gain realized from the grid IE to electrode 2|, an overall gain was determined approximately corresponding to the overall amplification of the discharge device H).

The overall gain of discharge device I 0 is pref erably adjusted by adjusting the amount of regeneration in discharge device I 0. It is desirable to make the amount of regeneration such that linear operation of the stage including device it! is assured consistent with as high gain as possible. For purposes of analysis, the two stages may be considered to be equivalent to two sepa rate discharge devices, a triode and a pentode, connected in cascade, wherein the regeneration may be symbolized b a negative resistance of the dynatron type connected across the anode load of the triode.

The regeneration which comes into being is believed to be due to the negative transconductance from the second control grid I8 to the screen electrodes 2| and 22. This negative transconductance efiect is produced in accordance with the following considerations: The total cathode space current of device I0 is substantially independent of the voltage applied to the second control grid I8, which controls the distribution of current between electrode 2| on one side and electrode 22 and anode 20 on the other side. Since the two electrodes 2| and 22 are connected together, substantially equal and opposite effects are produced on the electrodes 2| and 22 and on anode 20 by a change of the voltage on the second control grid It. That is, if electrode I8 is made more negative, more space current tends to flow to electrode 2| and less'to electrode 22 and anode 20. trode 22, which shares its current with anode 20, is less than the increase in current to electrode 2|. Therefore, the net current to electrodes 2| and 22 increases with negative potential in elec trode l8, and current to anode 20 decreases. Consequently, the transconductance between second control grid I8 and anode 20 is positive, and the transconductance between second control grid l8 and connected electrodes 2| and 22 is negative. When, as in this instance, the current flowing to connected electrodes 2| and 22 produces a voltage drop across external resistance 26 in response to variations impressed on the main control grid I5, at least a portion of. that voltage drop is fed back to the second control grid l8, through coupling capacitance 29 for further controlling the electron stream in discharge device It! regeneratively by voltage on electrode I8. In Fig. 1, a negative resistance efifect which causes regeneration for signals of audio frequencies occurs between connected electrodes 2| and 22 and second control grid l8 considered as a But the decrease in current to elecgroup, since coup-ling condenser 29 is of low reactance for signals of audio irequency, and the cathode of device l0.

In the particular amplifier circuit shown in the negative transconductance between the control grid l8 and connected electrodes 2| and 22 so that the amount of regeneration in discharge device H! is also changed. That is, when the positive transconductance between the grid l8 and anode 20 is high, the negative transconductance between control grid l8 and. connecte grids 2| and 22 is also high.

For that reason, the amount of regeneration is adjusted by adjusting the anode output resistance 25. When anode resistance 25 is decreased below a critical resistance, the transconeductance between the control grid l8 of device in and anode 20 is increased so that device I!) breaks into oscillation, due to the corresponding increase in negative transconductance between control grid l8 and connected grids 2| and 22. The signal voltage developed across resistance 25 is, of course, equal to the signal current flowing therethrough multiplied by the resistance of resistance 25. By making resistance 25 high the transconductance of the device is lowered but the voltage developed across resistance 25 tends to remain constant.

It is desirable to make the resistance 25 as large as possible, consistent with high gain, not only for suppressing oscillation in device I0 but also for decreasing the current drain from Voltage source 23. Also, resistance 25 is made large so as to assure linear amplification of high in tensity signals applied between the grid l5 and cathode of device I0. Since a reduction of anode to cathode conductance takes place when the anode potential is reduced low enough to cause operation along the curved portion of the anode voltage-anode current characteristic in some discharge devices, thisoperating condition is not desirable for maximum gain and linearity but it may be necessary if no other means is used to suppress or control the amount of regeneration, and is desirable as means for reducing discharge current.

Another method of controlling the regeneration between the triode and pentode sections of discharge device I0 is to adjust the continuous operating potential of connected grids 2| and 22, for example, by adjusting the resistance 26 In general, the smaller the resistance 20, the more discharge device |0 approaches a condition of selfoscillation. When resistance 26 is made large, space current in electrodes 2| and 22 is reduced.

Regeneration in discharge device I0 is also affected by the amount of electronemission from the filament or cathode. It is not uncommon for the regeneration in device I0 to increase with a decrease in electron emission from the cathode of discharge device Id. In other words, as the VOlt age of source 20 is decreased, for example, due to prolonged current drain therefrom, the overall amplification of device It! tends to increase and thus a compensation is provided for the loss. of amplification resulting from the decrease in voltage of source 23 in prolonged operation of the hearing aid. Under certain conditions a change in voltage of the heating source 40 may cause a condition of self-oscillation. Variation in the circuit behavior due to change in heating source voltage 03 is minimized greatly when resistances 25 and 26 are suitably large.

A possible explanation for the increase in regeneration when filament emission is decreased may perhaps'be that there is a reduction in emission so that all electrode potentials rise. large anode and screen electrode resistances are used to force operation of the pentode part of the Sinc gain and regeneration.

when anode and screen potentials rise, the dynamic transconductance of both anode and screen electrode increase with a' consequent increase in The transconductance between the electrode l 3 and anode 20 is increased and correspondingl the negative tran'sconductance' or regeneration in the triode stage is in creased. When resistances 25 and 25 are properly adjusted for high gain consistent with low current consumption in accordance with principles discussed herein, reduction of voltage of source 40 has appreciably no effect on operation of device Iil' over a large range of change of voltage of source 49.

Under certain conditions of adjustment, the resistances .24 and25=ma have such relative mag nitudes that the electrons constituting the space charge are attracted to connected electrodes 2! and 22 and anode 20 in such proportion that the respective positive and negative transconductances are substantially unaltered asthe space charge is reduced when the filament emission is decreased. This has been observed when resistance 2515s of the, order of 700,000 ohms and resistance 26 is of the order of 80,000 ohms, device ll] being a 1R5. 7

In a-demonstration to show the maximum overall gain obtainable by using device H], the plate load resistance 25 was reduced so that it was almost smallenough for the production of self-sustained oscillations in discharge device it. Withv l oq microvolts input; the output voltage was 1.4

volts. This corresponds t an overall gain of 14,000 in one discharge device. Such gain is usually not conveniently usable because of the greater diificulty of proportioning resistances 25 and 26 to avoid self-sustained oscillations as the voltage of source to drops.

8 tensityi's applied between main control grid l and the cathode of discharge device l0, an instantaneously decreasing current correspondingly flows through resistance 25; That is, the effective transconductance between grid l5 and anode 20 is negative in character. This is in line with the theory that device Hlincludes two-amplifying devices in cascade whereinas is well known the effective transconductance between the grid of the tensity of signals; applied between grid IE and itscathode.

When the resistance 25 is increased, the amount of regeneration in discharge device In is decreased, the amount of space current flowing to anode 2B is reduced, and consequently the overall gain is decreased. Also, when the resistance 26 is increased, the amountof space current flowing to screens 2| and 22 is reduced, and the overall gain is decreased. When resistance 25 or resistance 26 is made small, the space current flowing through the corresponding, resistance 2-5 or 26 is increased, and the overall amplification increases to a point where the amplifying circuit changes abruptly into a state of self-oscillation. Just before such self-oscillation begins, amplification is great, there i is enhanced linear orirequency distortion, en-

The circuit shown in Fig. 1 has much advantage total amount approaching 360 or ,a multiple thereof, including the phase shift in the amplifier.

This necessitates either carrying the phase shifting operation over two tubes, each one of which shifts the'phase 180, or using a transformer for phase inversion. Systems incorporating such means .areiinferior in stability and frequency.

range to the amplifying system as disclosedherein incorporating a single discharge device with are sistance load, because such systems must all transfer signalsthrough at least two filter meshes in the feedback loop to obtain the 360 phase shift through the entire feedback loop, while the pres-.,

ent arrangement requires but one mesh including resistances 2E and 21 and condenser 29 to complete the entire feedback loop for shifting signals 360; or, if it be preferred, 0. That is, there is no phase shift desired in translation of signals through the single mesh comprising resistances; 26 and 2'! and condenser 29, signals on grids 2!.

and ZZbeing effective to produce regeneration when impressed in phase ongrid H3; The re generative efiect is correspondingly constant over 'a frequency band limitedf only by the signal transferring ability for which the mesh including justed. V 1. 7 j

, When a signal of increasing instantaneous inhanced instability and the anode voltage is not 7 sufiicient to accommodate'signal voltage changes,

so that signals so greatly amplified are; distorted.

Such adjustment is undesirable. 'B making the resistance 25 verylarge for high gain and low current consumption, regeneration is reduced sufficiently that the device H! is highly linear and yet has great gain for amplification of small signals. It is thus seen'that, in general, when the amount of space current flowing in device Ii] is also. It is understood, of course, that such space current flow in varying degree isthe same as varying current drainfrom source '23.

resistances land/.27 and condenser 2% is ad- Adjustment made in increasing the size of resistance 25 to cause more linear operation and tosuppress self-oscillation and reduce discharge current is quite different from that present, in

known self-oscillation circuits having a resistance in the anode circuit. That is, inthe amplifying oscillating circuit of a 'multivibrator, having a resistance in the anode circuit, self-oscillation is suppressed when such resistance is made smaller, whereas in the arrangement shown in Fig- 1; self oscillation is suppressed by increasing resistance 25. I

With a constant output voltage across resist* linear operating conditions. Consequently, when plate coupling resistance 25 is increased, compensation is introduced for nonlinear conditions prevailing when resistance 25 i small.

Since the resistances 25 and 26 influence regeneration and linear operating conditions of device IO, and since they are connected in separate series circuits, including the common voltage source 23, their relative sizes influence the operating conditions of device i0.

When resistance 25 is increased, the overall transconductance of device it tends to decrease; and it is then desirable to have resistance 26 relatively small, consistent with linear operating conditions, so as to provide a compensation for the loss in gain due to increase in resistance 25. That is, when the ratio of resistance 25 to resistance 26 is increased, the overall gain 'of device i tends to be less afiected by a change in resistance 25 even though a greater and more linear voltage amplification is produced when resistance 25 is increased. That is, when resistance 26 is small compared to resistance 25, greater linearity is achieved than when the resistance 25 is comparable to resistance 26. Also, when resistance 26 is small compared to resistance 25, variations in heating voltage source 40 have little effect on the operating conditions of discharge device H1.

The modified arrangement in Fig. 2 diifers from the arrangement shown in Fig. 1 in that the space current for the anode 20 of device It] does not flow through the volume control resistance 24. In Fig. 2, the volume or gain of device In is controlled by adjusting the volume control resistance 24 or adjusting the amount of space current flowing through resistance 24 and to the screen grids 2| and 22.

To accomplish this type of volume control in I Fig. 2, the resistance 25 has one of its terminals connected to the anode 29 of device I0 and its other terminal connected to the positive terminal of source 23 and, as in Fig. 1, one of the terminals of volume control resistance 24 is connected to the screen grids 2| and 22 and the other terminal of resistance 24 is connected to the positive terminal of source 23. Otherwise, the circuit arrangements in Figs. 1 and 2 are the same.

The circuit of Fig. 1 is preferred over the circuit arrangement of Fig. 2 since it is found that when in the arrangement shown in Fig. 2 the resistance 24 is increased to a relatively high magnitude, the potential on the grids 2| and 22 decreases, the overall conductance of device I0 decreases, the potential of anode 20-increases, and device l0 tends to oscillate. When, as in the preferred form of the invention in Fig. 1, space current from anode 20 and scren grids 2| and 22 flows through volume control resistance 24, the current flowing through anode 20 is maintained relatively small and device I0 is less prone to oscillate.

' In Fig. 1, adjustment of gain control resistance 24 causes a direct adjustment in the continuous potential of anode 20 and screen electrodes 2| and 22 and causes a change in overall gain of device In In Fig. 2, adjustment of gain control resistance 24 causes an adjustment in the continuous potential of screen electrodes 2| and 22 and causes a change in overall gain of device I 0, and, of course, the anode potential is changed in the opposite sense in accordance with the above considerations.

It has been found that with the volume control arrangement shown in Fig. 1, a more suitable 10 range of volume control may be produced with a given size volume control and, more important, the minimum gain of device I!) may be made small.

A particular feature of the present invention resides in the arrangement of volume or gain control resistance 24 in relation to the other circuit elements shown in Figs. 1 and 2. Resistance 24 serves not only to control the gain of device I0 without causing self-sustained oscillations in device IE), but also serves to limit the amount of space current flowing through device In. This feature is of particular importance in battery operated hearing aid circuits wherein the cost of replenishing batteries is of importance. That is, resistance 24 is a combination gain control and current limiting or battery saving device, In general, the smaller the gain of the amplifying stage It, the smaller is the amount of space current flowing in device l0 so that the user of the hearing aid circuit shown herein controls to a certain extent the amount of current from battery 23.

While the two preferred methods for controlling the gain of device |0 are shown in Figs. 1 and 2, it is understood that other means may be employed for controlling the gain of device I0. For example, the gain of device Ill may be controlled by varying the magnitude of resistance 21 as shown in Fig. 3, or by varying the magnitude of resistance 25 as shown in Fig. 4, or by varying the magnitude of resistance 26 as shown in Fig. 5,

or by applying a fractional part of the voltage appearing across resistance l6 between grid I5 and cathode of device ID as shown in Fig. 6, or by applying a fractional part of the voltage appear-- ing across output resistance 32 between the main control grid and cathode of device M as shown in Fig. '7.

Although the modifications in Figs. 3 to 7, inclusive, show other means for controlling the gain of device IE, it is understood that the arrangements shown in Figs. 1 and 2 are preferred in that order, because (1) a greater control is available for controlling the amount of regeneration in device l0, especially when the magnitude of source 40 becomes relatively small, and (2) the user may exert some control over the amount of space current flowing through device Hi.

In a practical embodiment of the present invention, the various circuit elements described herein had the following properties: discharge device Ill-1R5 R, C. A. type, resistance |G--5 megohms, resistance 24-400,000 ohms, resistance 25-680,000 ohms, resistance 26-68,000 to 82,000 ohms, resistance 2'|10 megohms, resistance 32- 4.7 megohms, condenser 28--.l microfarad, condenser 29-100 micromicrofarads, condenser 3|- .001 microfarad.

While the particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects, and therefore the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

I claim:

1. A substantially linear high gain amplifier circuit including an electron discharge device having a cathode, a main control grid, a second control grid, an electrode and an anode, means for supplying space current between the anode and cathode of said discharge device, means including the electrode and second control grid. for prol g ne t res stance gect s id s cond 6. mm rid. be n a ran ed to. ha .mu anc respect to said electrode whereby the negative transconductance of said electrode causes regenoration, and a variable combination space current limiting and gain control resistance connected in se ries bircuit with said electrode and with said anode to control smiultaneously the flow of continuo-us space current to said electrode and anode.

,2. A substantially linear high gain amplifier circuit including electron discharge device having a cathode, a main control grid, a second control grid, an electrode and an anode, means for supplying space current between the anode and cathode, of said discharge device, means for supplying space current between the electrode and cathode "of said device, means, for impressing avoltage from said electrode on said second control grid, said second control grid being rranged to have simultaneously a positive transconduct ancewith respect to the anode and a negative transconductance with respect to the electrode, whereby the negative transconductance of said ec r d s su h as o ause re eneration. in sl phase as to cause self-sustained oscillations, means for. impressing signal voltages between said main control grid and cathode, means. coupled to said anode for developing output signal voltages means for reducin said regeneration whereby the intensity of saidjoutput signals varies substantially linear with the intensity of the input signals over the range of, input signals, and variable resistance means connectedseriallywith aiflail deand said e ectrode to adjust s multa ously the flow of continuous space current to said electrode and anode to control the gain oi"v said amplifier circuit.

3. A substantially linear high gain amplifier circuit including an electron discharge device having; a cathode, a main control. grid, a. second control grid, an electrodeand ananode, a Voltage source connectedbetween the;cathode and anode fordelivering space current to the dischargerdevice, means arranged tosupply space'current to said electrode means for applying, input. signal voltages between the main control grid and cathode, coupling means. between said electrode and second control grid, said secondlcontrol grid being arranged to have simultaneously. a positive transconductance with respect, to the anode and a negative transconductance with respect. to:said electrode whereby the negative transconductance of said electrode causes regeneration, a high resistancecoupled to the anode. forhigh gain and for limiting the current flow in the discharge device, said resistance aiiecting said positiveand negative transconductance, and a variable combinationspace current limiting andgain control resistance connected in series circuit with said electrode and saidanode to adjust. simultaneously the flowof, continuous space current to said electrcdeandanode to controlthe gain of said amplifier circuit.

4. An amplifier circuit including an electron '12 hac auce lement. connected etween aid' two spaced elcctrodesiand the second control grid'a re stan e clc nt connected between the second control grid cathode, a combination coup and voltagedropping resistance having onezof: its terminals connected to. said'two. spaced electrodes, a capacitance element vccnnected between the t o e and oth r terminal. of the-lastnientioned resistance, a combination coupling and voltage dropping resistance having one of its terminals connected to the anode, a, third voltage dropping resistance, a voltage source'for supplying space current to said discharge device, said voltage source being connected between'the' cathode and anode-through a series circuit including the second and third mentioned voltage dropping resistances, said voltagev sourcelbeing connected: be.- tween the, cathode, and said two. spaced electrodes through a series circuit including theffirst and third mentioned voltage droppingj resistances, and means for utilizing the voltagedrop across said resistance connected tothe anode, said third Voltage dropping resistance beingvariable for'ad's justing the gain in the amplifying circuit.

5. A substantially linear high. gain amplifier circuit including an electron discharge device having a cathode, a main control grid, a second control grid, an electrode andan anode, means for supplying space current between the anode and the cathode of said discharge device, means including the electrode and second control grid for producing a negative resistance efiect, said second control gridbeing arranged-to have simultaneously a positive transconductance with respect to theanode and a negative transconductance with. aid electrode whereby the negative transconductance of said electrode causes regeneration, and a combination space current limiting and gain control resistance connected in series circuit with said electrode and with said anode to control the amount of continuous space current flowing thereto. H

6. A substantially linear high gain amplifier circuit including an electron discharge device having. a cathode, a'main control grid, a second control grid, an electrode, and-an anode, a voltage source connected between the cathode and anode for delivering space current to the discharge device, means for applying input signal voltages between the main controlgrid and oathode, coupling means between said electrode and second control grid, said second control lid being arranged to have simultaneously a positive transconductance with respect to theanode and a. negative transconductance with respect to said,

electrode whereby the negativetranscqnductance of said electrode causes regeneration, a high reisistance couplcd-tothe anode for-high gainaud for. limiting the current fiow in the. dischargede vice, said resistance affecting said positive and negative transconductance, and a, combination discharge device, said electron discharge device,

having a cathode, a main control grid, 2. suppressor grid and an anode, said suppressor grid-being connected to the cathode, two spaced electrodes connected togetherand disposed between the suppressor-grid and-main control grid,.atsecond. control, grid disposed between, the two spaced electrodes, means for applying a. signal voltage. bee

tween themain control gridand, cathode, a ca-.

space current limiting and gain control resistance connected in series circuitwith said electrodeand,

said anodeto control the'a mount otcontinuous space current flowing thereto. 4

7. An electron discharge device. including. 'a source ofz-electronsand a first anode, a central electrode and a seconcl'anode mounted;inthatv order. at. increasing distances, respectively, from said source, saidifirst anode beingcoupled ex,- ternally to said control electrode, whereby current changes in-said first'anode are reenforcedby action of said control electrode, a source of operating potential for said;firstand secondanodes, said last mentionedsource having a nega- 13 i4 tive terminal connected With-said electron source REFERENEES CITED and a positive terminal first and Second limped The following references are of record in the ances connected between said positive terminal file of this patent:

and said first and second anodes, respectively, and

means for simultaneously varying the impedance 5 UNITED $TATES PATENTS between said terminal and said. first anode and Number Name Date the impedance between said terminal and said 2,22 030 Herold Jam 7 1941 second anode in the same sense and at substan- 2,342,492 Rankin at Feb, 22 1944 tially the same rate, whereby the ratio of said 2,226,561 Herold Dec. 31, 1940 impedances is maintained within a predetermined 10 2,287,280 Terman June 23, 1942 range of funpedances, 2,235,817 Freeman Mai. 25, 1941 2,262,916 Boucke Nov, 18, 1941 GILBERT E. GUSTAF'SON. 2,214,614 Hunt Sept. 10, 1940

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