US2619622A - Gaseous electron tube circuits - Google Patents

Description

Nov. 25, 1952 E, o. JOHNSON GASEOUS ELECTRON TUBE CIRCUITS Filed Jan. 2, 1951 INVENTOR E OWAAD 0 Ja/rmso/v ATTORNEY Patented Nov. 25, 1952 GASEOUS' ELECTRON TUBE CIRCUITS EdWardOscar Johnson, Princeton, N. .L, assignor to Radio Corporation of America, a. corporation of Delaware Application January 2, 1951,.Serial,No. 203,948

15 Claims. 1

This invention relates-to electrontube circuits utilizing gaseous electron-tubes, which provide continuous control 1 of anoperating characteristic, such" as'outputcurrent, through internal tube action. More particularly this invention relates to electron tube-circuits utilizing gaseous electron tubes in which thecurrent flowing in an ionization circuit is-operative to'control or to enable continuously variable control of the current in a work circuit connected with the tube.

It is Well known in the electron tube art that the space charge limits the'current that may flow in an evacuated electron tube and that this limitation can'be overcomebyproviding a small quantity of gas in thetube envelope. If the potentialbetween the electron emitting and collectingelectrodes of the tube is'sufliciently high, the gas becomes ionizedby electron bombardment of the gas molecules, thereby'develop-ing positive .ions which will neutralize the negative space charge formed by the electrons. The combinedcloud'ofr. ions and electrons then act as an excellent current conductor, allowing thetube current to rise very rapidly until the full electron 1 emitting capacity of: the electron emitter electrode'is attained.

While the phenomenon, briefly described above hasconsiderab'le utility, there are several char acteristics' of gas filled'. tubes which heretofore have imposed limitations; on 1 their use.

In orderzto ionize the gasin the tube, a certain minimumrvoltage is required, as-determined'by the I tube geometry and: the type ofgas used. Briefly; this isdue to' theiact' that acertain amount of energy must be imparted to an atom or molecule;inxorder'tocause an electron to be liberatedfrom the-energy confines of theatom or molecule. In the case of a gas tube, this'means that the bombarding: electrons must be given a certain minimum velocity soas to provide sufficient energy to cause and sustain the electron liberation or ionization of the tube gas. To give these ionizingor bombarding electrons'this minimum velocity, a corresponding minimum potentialor arc drop" must be maintained between an electron emitterelectrode and an electron collector electrode immersed in: the gas. In conventional gas tube systems, this are drop is a minimum potentialf which is unproductive where a principal objective is to transfer potential from a. source to a load with the least possible loss in the system.

The effective and eflicient control of the gas tube current is another problem in conventional gas tubes. In a conventional vacuum tube; a control electrode placed between the electron emitting and electron collecting electrodesv provides a very eflicient andefiective means for controlling the tube'current. A very small'change in the control electrode potential will have arelatively large effect on the outputcircuit of the tube, as is well known, it being possibleto vary the tube current smoothly and continuously within relatively wide limits by varying the-control electrodepotential.

The above described mechanism of gas-tubes has beenunder-study for'many years in an effort to provide a tube capable of a large work-0r output circuit current while enabling continuous variable control of the tube by internal tube action.

Various systems of control'have been devised, among which is one providing for'theuse: of velocity modulation of a plasma generating-elem tron stream and having a temperature controlled cathode. This system is disclosed in U. S. Patent 2,213,551, issued to H. Nelson, September 3, 1940, for Electron Discharge Device. Nelson clearly discloses that the total current in his control circuit remains constant and that a temperature controlled cathode is used as a" current limiting device. Such a system is linear for only small changes in voltage and is subject to distortion due to temperature variation;

U. S. Patent 2,034,571, issued March 17, 1936, to C. G. Found for Electrical Disch'arge'Device and Method of Operating: Same, providesanother type of gaseous electron tube utilizing an additionalpair ot'electrodes to provide a plasma generating circuit; However, here againrdue to the inherentlimitations of thesystem'the grid control usually attributed to vacuum'tubes cannotbeattained;

In axcopending application. of1E. 0. Johnson; Serial No.-185,745, filed September20, 1950, and assigned to the assignee of'the present invention, there is described'and claimed a-gaseous electron tube capableof continuous grid control action. As pointed out in greater detail in that application, the usual loss of grid controlina gaseous electron tube upon ionization is-avoided by providing separate paths for the ionization currents and the load currents and by providing in the workcircuit a potential lower thanthat required to produce ionization. Because. thepotential available in the load circuit is insufficient to produce ionization, an. auxiliary source of ionization potentialisprovided to fill this need and since only this source is energized with a sufiiciently large potential to produce ions it is unaffected by signal variations in the form of.

either changes in the potential of the control grid or changes in the load currents which are produced thereby.

Accordingly, it is an object of this invention to provide circuit means for operating gaseous electron tubes of the type providing efiective grid control action as shown, described and claimed in the aforesaid pending application.

t is another object of this invention to pro vide circuits capable of enabling maximum utilization of continuously variable grid controlled gaseous electron tubes of the type referred to for the control of electrical energy flowing in associated work circuits and the like.

It is a further object of this invention to provide circuit means in which small current variations in a control circuit are utilized to control continuously by means of gaseous electron tubes, relatively large amounts of current or power in a load circuit. It is an ancillary object of this invention to provide means for applying control signals to a gaseous electron tube and for connecting a load circuit to the gaseous electron tube in such a manner as to enable multi-signal control of a single load circuit through the single gaseous electron tube means.

In accordance with the present invention, there is provided circuit means which may be connected between any two or several electrodes of a gaseous electron tube of the type capable of providing continuously variable control, by

means of resistor-capacitor coupling, transformer coupling or other forms of coupling to provide in a load circuit of the tube, an outputsignal which is directly proportional to a control signal applied between any two of said electrodes, or which may be proportional to the relative phase and magnitude of the various applied signal potentials.

A further understanding of the invention may be had by reference to the following description of certain illustrative embodiments thereof when considered in connection with the accompanying drawing, in which:

Figure 1 is a schematic circuit diagram illus- I trating one embodiment of the invention wherein a gaseous electron tube is utilized to control a motor circuit;

Figure 2 is a view in cross section of a gaseous electron tube as utilized in control circuits embodying the invention;

Figure 3 is a schematic circuit diagram illustrating a further embodiment of the invention, wherein a gaseous electron tube is utilized to control the phase and magnitude of a generated alternating-current voltage in accordance with certain characteristics of control potentials or signals from a plurality of control sources;

Figure 4 is a schematic circuit diagram illustrating a still further embodiment of the invention, wherein two elements of a gaseous electron tube are utilized to control an anode output or work circuit;

Figure 5 is a schematic circuit diagram illustrating another embodiment of the invention, wherein a gaseous electron tube is utilized as a cathode-coupled device to directly drive the voice coil of a transducer element;

Figure 6 is a schematic circuit diagram illustrating still another embodiment of the invention, wherein a gaseous grid-controlled electron tube is utilized as a current regulator and wherein negative feedback is applied from an anode circuit to a grid circuit to establish more uniform control; and

Figure 7 is a graph showing curves illustrating the relationship between the current and the voltage of the load circuit of an electron tube adapted for use in a circuit embodying the invention, with different applied control-grid potentials.

Referring to the drawing in which the reference characters designate like parts and circuit elements throughout the various figures, and referring now particularly to Figure 1, there is illustrated a gaseous electron tube In having an anode I2, a main cathode I4, an auxiliary cathode I6 and a shield I8 for the auxiliary cathode. The anode I2 and the main cathode I4 provide a diode section through which load currents can be passed in the manner of a conventional gas diode. The auxiliary cathode I6 is an additional electron emitting electrode which cooperates with the anode I2 and main cathode Hi to provide a separate circuit within the tube envelope for ionization of the tube gas. In order to provide operating potentials for the tube H a source of direct-current potential or battery 20 is connected across a voltage divider resistor 22. All intermediate tap 24 on the resistor 22 is connected to the main cathode I4 and the negative potential end of the resistor 22 is connected through a cathode resistor 26 and the space path of an electron tube 28, to the auxiliary cathode I6, thereby providing between the main cathode I l and the auxiliary cathode I6 a sufiiciently high potential to cause ionization of the tube gas. A pair of bypass capacitor 30 and 32 are connected across the respective sections of the voltage divider resistor to prevent signal currents from affecting the level of the potential available.

The electron tube 28 is utilized as a signal input device to effectively modulate the ionization current which will be drawn between the auxiliary cathode I6 and the main cathode I4 of the gaseous electron tube Hi. It is, of course, believed to be obvious that the modulation control established by the electron tube 28 can also be provided by other coupling means such as a transformer or a fixed or variable resistor, and that an electron tube is shown merely for illustrative purposes as a presently preferred means. In the embodiment shown, an input signal is applied between the control grid 34 and the cathode 38 of the electron tube 28 to vary theimpedance of the space path, thus producing between the auxiliary cathode I6 and the main cathode I 4 voltage variations which are reflected by corresponding changes in the ionization-current of the tube I9.

The load circuit is completed, as shown in Figure 1, by connecting the field Winding 38 and armature 39 of a shunt-connected direct-current motor 56 between the anode I2 of tube I0 and the battery 25, being connected in the present example to the high potential or positive terminal of the voltage divider resistor 22. It should be noted that the potential available in the load circuit, that is, the potential available between the high potential. end of the resistor 22 and the intermediate tap 24 is less than that required to cause ionization of the gas in the gas tube l0.

When a gaseous electron tube, as shown, described and claimed in the above-identified copending application by E. 0. Johnson, and which the tube It represents, is connected in this manner, ionization or breakdown oi the gas occurs between the auxiliary cathode I 6 and the main cathode [4 of tube 10. There is thus provided within the tube envelope, :a plasma which acts as an excellent conductor to provide, in effect, a low resistance connection bet-ween the main cathode l4 and the anode 12 of the tube ill. Since, as is' well known in the art, the density of the plasm enerated in the tube will be controlled, at least in part, by the amount of current :flowing through the ionization circuit, the reflective resistance between the main cathode l4 and the anode I2 of the tube Ill can be effectively controlled by externally controlling the current flow in the ionization circuit. In the embodiment shown in Figure 1 this ionization current control' is provided by signal or control potentials applied by means of the electron tube v2.8.

Ina gaseous electron tube 01' the type utilized,-

the conductivity between the main cathode i4 and'the anode not the tube In is a function of the density of the plasma existing within the tube envelope. Accordingly, it is seen that since the ionization current fiowing between the auxiliary cathode l6 and the main cathode 14 is effective to control the plasma density any change in ionization current causes a change in the conductivity between the anode l2 and the main cathode l4 of the tube in. A change in the conductivity thus produced is effective to cause a resulting change,

in the current flowing in the load circuit which, as shown in Figure 1, is connected between the anode l2 and the main cathode i4 ofthe tube [0,

The characteristics of the type of gaseous electrontube utilized are such that a relatively small electron tube HI of Figure 1, that may be utilized inthe circuits of the present invention, is shown by way of example. Within the tube envelope, a U-shaped anode 12 of sheet metal is disposed external to and in juxtaposition with a control grid 42 oi relatively coarse spacing. The main cathode .44 is mounted within and is partially sur rounded bythe control grid 42 and the anode If. #Theauxiliary cathode I6 is mounted coaxially with respect to a slotted cylindrical shield 18. Thus the. tube lmay be provided with a control grid 42 interposed between theme-in anode llland the main cathode I 4;

' As shown in Figure 2, the elongated narrow slot in the shield l'8 is positioned withits center extending along a plane passing through the axes of the auxiliary and main cathodes I4 and .18. It has been found that the desired degree of ionization may thus be attained with a considerable reduction in the power required to. sustain ionization.

The schematic circuit diagram illustrated in Figure 3 of the drawing, to which attention is now directed, shows an embodimentof the invention wherein the load circuit is controllable by a plurality of control potentials or signals in connection with the tube of Figure 2. A first control signal is coupled to tube by means. of a conventional vacuum tube 44 having an anode 45 connected to the control grid 42 of tube I'd 6 and a cathode-48 connected to the auxiliary cathode 16 of tube .Hi. Control signals or potentials may be applied between the control grid 50 and the cathode 48 of the control tube 44 from any suitable source (not shown). A grid resistor 52 and a bias battery '54 connected in series arrangement between the control grid 50 of the control tube 44 and a point of fixed reference potential or ground provide the necessary grid bias for the control tube 44. Signal currents are prevented from affecting the bias battery 54 by a bypass capacitor 56 which is connected in shunt with the bias battery 54. Energizing potential is applied to the anode 46 of the control tube 44 through an anode resistor from B+ which represents the positive terminal or a source of energizing potential (not shown) When signal voltages are impressed between the control grid and the cathode 48 of the conformer 64 which are connected in series betweenthe anode I 2 and the main cathode I4 of the tube H).

The direct-current motor 60 in the load circuit of the tube I0 is mechanically coupled with an alternating-current generator 12 having an output current and voltage which is controllable by controlling the motor 50. In order to provide a control signal which will be in accordance with the output of the alternating-current generator 12, the output circuit of the generator 12 is coupled to the primary winding 14 of a coupling transformer 1-6. The secondary winding 18 of the coupling transformer 16' is connected between the auxiliary cathode l6 and the shield I8 01' the tube HI. There is thereby impressed between the auxiliary cathode I6 and the shield l8 of the tube -9 a signal voltage which is representative in phase and magnitude of the output voltage and current of the alternating-current generator I2. Three distinct control signals are, therefore, coupled to the various circuits of the gas tube 18 illustrated in Figure 3 of the drawing", the signal coupled between the control grid 42 and the auxiliary cathode It by means of the control tube 44, the signal coupled to the load circult by means of the power'transformer 64 and the signal coupled between the shield l8 and the auxiliary cathode by means of the coupling transformer 15. The characteristics of'the tube Ill are such that once breakdown or ionization h-asbeen caused by the application of potential between the main cathode l4 and the auxiliary cathode 8 the current flowing between the main cathode l4 and anode [2 will be directly proportional to the relative phase and magnitude of the potentials applied between any two of the tube electrodes. Accordingly, it is seen that the load current in the schematic circuit diagram shown in Figure 3 of the drawing will be proportional to the relative phase and magnitude of the source of alternating current, the alternatingcurrent output of the generator 12 and the separate signal supplied through the control tube 44.

There has thus been provided a simple circuit in which the output current and voltage of a generator 12 is automatically controlled in accordance with the source of power driving the generator and the output current and voltage of the generator itself. Additionally, a distinct and separate control facility is provided to allow an operator to make any adjustments or changes that might be necessary without having to come in contact with the high power load circuit, through control of the potentials or signals applied through the coupling tube 44.

In the schematic circuit diagram of Figure 4, illustrating a further embodiment of the invention, a resistor 8!} representing any suitable cou-. pling impedance means, which is common to both the load circuit and the ionization circuit, such as a coupling transformer or an electron tube, is utilized as the input impedance to control the current through the load circuit of the tube ID. The tube Ill may, as indicated, be identical with that illustrated in Figures 2 and 3 of the drawing. The load circuit in this instance is an impedance indicated by the'rectangle 82 which is connected in series with a first source of direct-current potential or battery as and the input resistor 89, to the main cathode l4, thereby completing the circuit between the anode l2 and the main cathode l4. A signal bypass capacitor 86 is connected in shunt with the battery 84 in order to insure that the level of potential is unaffected by variations in the signal level.

In order to complete the ionizing circuit for the gaseous electron tube It, a second source of direct-current potential or battery 38 is connectedbetween the common terminal of the first battery- 84 and the input resistor 88 and the auxiliary cathode 16 of the tube it. As in the first instance, this second potential source 88 also is shunted by a signal current bypass capacitor 90. Asthe control grid 42 is not utilized for control purposes in this arrangement, it is shown as connected directly to the main cathode It, although alternatively it may be connected to other suitable points in the circuit such as directlyto the anode l2, to serve the same purpose.

As above discussed, the second potential source 88 provides sufiicien-t potential to cause ionization of thegas in the tube I0. It is further noted that under normal operating conditions the first potential source 84 would normally provide a potential which is less than that required to cause that immediately upon this occurrence the ionization circuit comprising the main cathode M and the auxiliary cathode It would assume the function of providing plasma within the tube envelope and the potential drop existing between the main cathode I4 and the anode l2 of the tubeill would immediately fall to a potential in the order of of a volt which, of course, is insufiicient to maintain ionization between these two electrodes. There is thus provided an arrangement wherein the input signal voltage is effectively coupled in the main cathode circuit of the tube i E]. This type of coupling is generally referred to as cathode. coupling. However, it is to be noted that since the resistor 80 is a part of the ionization circuit connected between the main'cathodell and the auxiliary cathode l6, signal voltages applied to the resistor 80 will produce a corresponding change in the ionizing current, which as above discussed in connection with'Figure 1 will be effective to control the current flowing in the load circuit.

The schematic circuit diagram shown in Figure 5' is illustrative of a further embodiment of the invention wherein a gaseous electron tube l0, identical with the tube ID of Figures 2; 3 and 4, is utilized to directly drive the voice coil 92 of a transducer device94 such'as a loudspeaker. The load circuit of the tube It comprises a first battery or operating potential source 84 which is connected between the anode l2, tube [0 and one side of the voice coil 92. The load circuit is completed by directly connecting the other side of the voice coil 92 to the cathode [4 of the tube H). [As above discussed in connection with Figure 4, the control grid 42, which is not utilized for control purposes in thiscircuit, is directly connected to the anode [2 of tube l0. There is provided as discussed in connection with Figure 4, a signal bypass capacitor 86 which is connected in shunt with the first battery 84. It is seen, therefore, that the work circuit actually consists of an output circuit commonly referred to as being cathode coupled. In other words, the output impedance, which consists of the voice coil 92 is connected between the cathode and the negative side of the source 84. The ionization circuit for the tube: l0 com prises a second or potential souce 88, having a shunt-connected bypass capacitor 90, connected in series with a cathode resistor 96 and the space path of an electron. coupling tube 98 between the common terminal ofthe voice coil 92 and the auxiliary cathode l6 of the tube 10. Input signals areapplied to this circuit-by coupling the output of an amplifier, phonograph, or other source 99 of signal, between the control grid I00 and the cathode I02 of the electron coupling tube 98. Input signals thus applied produce potential variations in the ionizing circuit which, as above discussed in connection with Figure 1, are efiective to modulate the current flowing in the load circuit of the tube It). It has been observed that the relationship between input signal voltages and output signal voltages obtainable from a circuit as shown in Figure 5 arranged in this manner is substantially linear throughout the entire working range.- The low impedance obtainable inthe type of gaseous electron tube as utilized by-the present invention provides excellent coupling to such low impedance load devices as loudspeakers. It has long been a problem in the-audio frequency field to provide an output circuit for an amplifier capable of low impedanceand low distortion. Outputtransformers which are generally required as coupling devices between the high impedance anode circuit of an electron tube and the low impedance voice coil of a loudspeaker frequently limit the quality obtainable in an audio frequency circuit. The circuit shown in Figure 5 obviates these problems'by providing a low impedance, substantially linear coupling circuit without the use of couplin transformer.

In View of the high current capabilities and the particular characteristics of the triode section of the gaseous electron tubes utilized by the present invention, these tubes provide excellent control for current regulator systems. Such a 9. system is illustrated in Figure 6 of the drawing. In a regulator of this type, the general problem to be overcome is the variation in the current available at a load under diiferent load conditions. In the embodiment illustrated in Figure 6, the source of current to be regulated is shown as'a battery 84' which is connected in series with a load impedance, indicated by the rectangle I04, and the'primary winding I 06 of a feedback transformer lfls between the anode l2 and the main cathode H of a tube It). The ionizing circuit for the tube l comprises a potentiometer H0 which is connected in series arrangement with a second battery or potential source 88 between the main cathode l4 and the auxiliary cathode [6 of the tube l0. A bypass capacitor 90 is connectedin shunt with the second battery 88 to prevent signal variations from affecting the source of potential. Control potentials for the control grid 42 of the tube Ill are provided by connecting the control grid 42 of the tubel0 through the secondary winding H2 of the'feedback' transformer I08 to a variable tap H4 on the potentiometer H0.

An examination of the curves shown on the graph illustrated in Figure 7 of the drawing may now be referred to for a further understanding of the operation of the present embodiment of the invention as illustrated in Figure 6- of the drawing. The magnitude of the voltage source is represented by the ordinate of the graph and the eurrant'to be regulated is illustrated as the abscissa. Three distinct curves A, B and C are illustrated which represent respectively different grid bias potentials, curve A representing the least potential and curve C representing the greatest potential 01'- the applied control grid bias potentials. Itis noted that in each instance the curve rises with a substantially constant slope to a knee which is determined by the magnitude of the grid bias potential. After passing the knee, each of the curves. A, B and C represents asubstantially constant current. However, without the feedback transformer I08 the slope of portion of the curve'above the knee may vary byas much as 5 per cent- It, therefore, appears to be obvious that if the circuit is operated beyond the. knee of the curve. any variations in load will not be reflected. by variations in the current flowing in the circuit.

This result is obtained due. to the fact that the current flowing in the work circuit is controlled by two separate factors. One of these factors being the plasma density existing in the tube and the other being thecontrol grid bias potential existing between. the. control grid 42 and the main cathode H of the tube In. If a greater current starts to flow in the load circuit, a. representative voltage will be transferred to the grid circuit by means of the feedback transformer 168 which will cause an increase in the negative grid bias potential, thereby tending to reduce the amount of current flowing in the load circuit.

There will also be a tendency to increase the current in the ionization circuit which will also produce a greater negative grid bias potential which will be applied to the control grid I and act-to reduce the current flow in the load circuit. It, therefore, appears to be obvious that the combined action of inverse voltage feedback and the increase in applied grid control potential through the increase in plasma density will provide adequate control. to establish constant current in the load circuit.

The operation of the above discussed embodiments of the invention are based upon the utilization of a gaseous electron tube ill in which the functions of providing ionization needed for space change neutralization and providing the field needed for drawing the required work current have been separated. In a gaseous electron tube of this type it has been found as illustrated in Figure 3 of the drawing, that voltage variations or input signals when applied between any two of the electrodes in the gaseous electron tube will produce in the load or output circuit a current and/or voltage variation representative of the applied signal variations. It has been found that a current of a few milliamperes flowing in the ionization circuit can be made to modulate and control a current of relatively heavy amperage in a work circuit.

In the embodiment of the invention illustrated in Figure 1 this control facility has been utilized to control the current through the shunt field 38 of the direct-current motor 40. Generally, control of this type requires the handling of excessively large currents. However, the combination provided by the present invention permits a conventional electron tube 28 having a grid control circuit which may be varied by small voltages to be utilized to control the very large currents circulating through the load circuit.

In the embodiment illustrated in Figure 3 of the drawing a gaseous electron tube I0 capable of continuous grid control action is utilized to provide control of a work circuit from a plurality of control sources. A first control signal is applied between the control grid 42 and the shield l8, a second control signal is applied between the shield l8 and the auxiliary cathode l6 and a third control signal is applied between the anode l2 and the main cathode M of the gaseous electron tube [0. Thus the single load circuit of such a tube may be controlled in accordance with two or more applied signal voltages by applying them between any two of the tube electrodes.

Cathode coupling as an input circuit as shown in Figure 4 and as an output circuit as shown in Figure 5 of the drawing, provides further flexibility for the utilization of the gaseous electron tube I 0. The substantially linear control provided by the ionization circuit provides an excellent circuit to control and drive a loudspeaker 9'4 when it is coupled to the cathode 14 of the triode section of the gaseous electron tube I0. It has been found that the characteristic of this type of gaseous electron tube are sufficiently linear to provide substantially distortionless output when utilized in any of the illustrated embodiments.

There has further been illustrated, as in Figure 6 of the drawing, that the large current capabilities of such a gaseous electron tube and the combined factor of continuous grid control of the load circuit can be utilized to provide an excellent current regulating device. It is, of course, obvious that such a gaseous electron tube could also be utilized in a voltage regulator system wherein a shunt current regulator is connected to establish substantially constant current through resistor to provide a constant voltage at a load under varying load conditions.

Accordingly, there has been shown that the aforesaid type of gaseous electron tube can be utilized efilciently and effectively under various circuit conditions Where grid control action is desirable to control high current circuits by means of low current or low potential control signals. Further, it has been shown that such a device may be utilized as a form of mixing circuit wherein the application of two or more control signals may be utilized to provide in a load circuit a voltage or current which is representative of the relative magnitude or phase of the applied control signal.

What is claimed is:

1. In a system for operating a gas filled electron tube of the type having a plurality of electrodes including an anode, a main cathode and an auxiliary cathode for passing ionizing current through the space path of the tube, and a shield electrode in proximity with said auxiliary cathode, in combination, an output circuit including a first source of energizing potential connected between said anode and another one of said electrodes, an input circuit coupled between said main cathode and one of said other electrodes, and a second source of energizing potential capable of delivering a potential greater than that required to cause ionization of said tube gas, said last named source being connected between said main cathode and said auxiliary cathode.

2. In a system for operating a gas filled electron tube of the type having a plurality of electrodes including an anode, a main cathode, a control grid between said anode and main cathode, an auxiliary cathode for passing ionizing current through the tube gas and a shield electrode in proximity with said auxiliary cathode, in combination, an output circuit including a first source of energizing potential capable of delivering a potential less than that required to ionize the tube gas and connected between said anode and another one of said electrodes, and a control circuit connected between said main cathode and said auxiliary cathode and including a second source of energizing potential capable of delivering a potential greater than that required to cause ionization of the tube gas.

3. In a system for operating a gas filled electron tube of the type having a plurality of electrodes including an anode, a main cathode, a control grid disposed between said anode and main cathode, an auxiliary cathode for passing ionizing current through the tube gas and a shield electrode in proximity with said auxiliary cathode, in combination, an output circuit including a first source of energizing potential capable of delivering a potential less than that required to ionize the tube gas connected between said anode and another of said electrodes, an input grid control circuit connected between said control grid and said auxiliary cathode, and a second source of energizing potential capable of deliverin a potential greater than that required to cause ionization of said tube gas and being connected between said main cathode and said auxiliary cathode.

4. In a system for operating a gas filled electron tube of the type having a plurality of electrodes including an anode, a control grid, a main cathode, an auxiliary cathode for passing ionizing current through said tube gas and a shield electrode in proximity with said auxiliary cathode, in combination, an output circuit including a first source of energizing potential capable of delivering a potential less than that required to ionize the tube gas connected between said anode and another of said electrodes, input impedance means connected between said shield electrode and said auxiliary cathode, and a second source of energizing potential capable of delivering a potential greater than that required to cause ionization of said tube gas and being connected between said main cathode and said auxiliary cathode.

5. In a system for operating a gas filled electron tube of the type having a plurality of electrodes including an anode, a control grid, a main cathode, an auxiliary cathode for passing ionizing current through said tube gas and a shield electrode in proximity with said auxiliary cathode, in combination, an output circuit including a first source of energizing potential capable of delivering a potential less than that required to ionize the tube gas connected between said anode and another of said electrodes, input impedance means connected between said shield electrode and said auxiliary cathode, means for applying a control current through said input impedance means, and a load impedance in said output circuit for deriving a current therefrom.

6. In a system for operating a gas filled electron tube of the type having a plurality of electrodes including an anode, a main cathode, an auxiliary cathode for passing ionizing current through said tube gas and a shield electrode in proximity with said auxiliary cathode, in combination, an output circuit including a first source of energizing potential capable of delivering a potential less than that required to ionize the tube gas and connected between said anode and another of said electrodes, an input, circuit coupled between said main cathode and another of said electrodes, an impedance connected in common with said main cathode and each of said anode and said auxiliary cathode, and a second source of energizing potential capable of delivering a potential greater than that required to cause ionization of said tube gas and being connected between said main cathode and said auxiliary cathode.

7. In a system for operating a gas filled electron tube of the type having a plurality of electrodes including an anode, a main cathode, an auxiliary cathode for passing ionizing current through said tube gas and a shield electrode in proximity with said auxiliary cathode, in combination, an output circuit including a first source of energizing potential capable of delivering a potential less than that required to ionize the tube gas and connected between said anode and another of said electrodes, said output circuit further including a load impedance, an input circuit connected between two of said electrodes, impedance means connected in common with said main cathode and each of said anode and said auxiliary cathode, a second source of energizing potential capable of delivering a potential greater than that required to cause ionization "of said tube gas and being connected between said main cathode and said auxiliary cathode, and signal input means for applying throughsaid impedance means a control signal to said tube to control the current flow in said load impedance,v

8. In a system for operating a gas filled electron tube of the type having a plurality of electrodes including an anode, a main cathode, a control grid between said main cathode and anode an auxiliary cathode for passing ionizing current through said tube gas and a shield electrode in proximity with said auxiliary cathode, in combination, a work circuit including a first source of energizing potential capable of delivering a potential less than that required to ionize the tube gas connected and betweensaid anode and another of said electrodes and for supplying work current through the space path of the tube, said work circuit further including a load impedance, an input circuit comprising a variable impedance device connected between said control grid and said auxiliary cathode to control the current flow in said work circuit, and a second source of energizing potential capable of delivering a potential greater than that required to cause ionization of said tube gas and being connected between said main cathode and said auxiliary cathode.

9. In a system for operating a gas filled electron tube of the type having a plurality of electrodes including an anode, a main cathode, a control grid between said main cathode and anode an auxiliary cathode for passing ionizing current through said tube gas and a shield electrode in proximity with said auxiliary cathode, in combination, a first source of energizing potential capable of delivering a potential less than that required to ionize the tube gas and connected between said anode and another of said electrodes, an input circuit coupled between said main cathode and one of said other electrodes, impedance means connected in common with said main cathode and each of said anode and said auxiliary cathode, and a second source of energizing potential capable of delivering a potential greater than that required to cause ionization of said tube gas and being connected between said main cathode and said auxiliary cathode.

10. In a system for operating a gas filled electron tube of the type having a plurality of electrodes including an anode, a main cathode, a control grid between said main cathode and anode an auxiliary cathode for passing ionizing current through the tube gas and a shield electrode in proximity with said auxiliary cathode, in combination, a work circuit including a first source of energizing potential capable of delivering a potential less than that required to ionize the tube gas and connected between said anode and another of said electrodes said work circuit further including a load impedance of high current passing capability, a control circuit connected between said main cathode and said auxiliary cathode and including a second source of energizing potentia] capable of delivering a potential greater than that required to cause ionization of said tube gas, and an input grid control circuit including an impedance means connected between said control grid and said auxiliary cathode.

11. In a system for operating a gas filled electron tube of the type having a plurality of electrodes including an anode, a control grid, a main cathode, an auxiliary cathode for passing ionizing current through said tube gas and a shield electrode in proximity with said auxiliary cathode, in combination, a work circuit and a first source of energizing potential capable of delivering a potential less than that required to ionize the tube gasfi said work circuit being connected between said anode and another of said electrodes, a control circuit connected between said main cathode and said auxiliary cathode and including a second source of energizing potential capable of delivering a potential greater than that required to cause ionization o fsaid tube gas, and an input impedance connected between said shield electrode and said auxiliary cathode.

12. In a system for operating a gas filled electron tube of the type having a plurality of electrodes including an anode, a control grid, a main cathode, an auxiliary cathode for passing ionizing current through said tube gas and a shield electrode in proximity with said auxiliary cathode, in combination, a work circuit connected between said anode and said main cathode and including a first source of energizing potential, said work circuit further including an output impedance of high current carrying capabilities, impedance means connected in common with said main cathode and each of said anode and said auxiliary cathode to control the work circuit current, and a control circuit connected between said main cathode and said auxiliary cathode and including a second source of energizing potential capable of providing a potential greater than that required to cause ionization of said tube gas.

13. In a system for operating a gas filled electron tube of the type having a plurality of electrodes including an anode, a main cathode, an auxiliary cathode for passing ionizing current through said tube gas and a shield electrode in proximity with said auxiilary cathode, in combination, a work circuit and a first source of energizing potential capable of providing a potential less than that required to ionize the tube gas, said work circuit being connected between said anode and another of said main cathode, a control circuit connected between said main cathode and said auxiliary cathode, said control circuit including a variable impedance for controlling the work circuit current and further including a second source of energizing potential capable of providing a potential greater than that required to cause ionization of said tube gas, whereby current in the order of milliamperes in the control circuit is effective to control a relatively greater current in flowing in the work circuit.

14. In a system for operating a gas filled electron tube of the type having a plurality of electrodes including an anode, a control grid, a main cathode, an auxiliary cathode for passing ionizing current through said tube gas and a shield electrode in proximity with said auxiliary cathode, in combination, a loudspeaker voice coil and a first source of energizing potential capable of delivering a potential less than that required to ionize the tube gas, said voice coil and said first source of potential being connected between said anode and said main cathode, a control circuit connected between said main cathode and said auxiliary cathode, said control circuit including a variable impedance means and a second source of energizing potential capable of delivering a potential greater than that required to cause ionization of said tube gas, whereby current through said voice coil is controlled in accordance with variations of said variable impedance.

15. In a system for operating a gas filled electron tube of the type having a plurality of electrodes including an anode, a control grid, a main cathode, an auxiliary cathode for passing ionizing current through the tube gas and a shield electrode in proximity with said auxiliary cathode in combination, a work circuit including an electric motor and a first source of energizing potential capable of delivering a potential less than that required to ionize the tube gas, said work circuit being connected between said anode and another of said electrodes, a control circuit connected between said main cathode and said auxiliary cathode, said control circuit including a first variable impedance means and further including a second source of energizing potential capable of delivering a potential greater than that required 15 16 to cause ionization of the tube gas, an input grid REFERENCES CITED control circuit comprising an electron tube con- The following references are of record in the nected between said control grid and said auxof this patent; iliary cathode, an input transformer connected between said shield electrode and said auxiliary cathode, and a second variable impedance con- UNITED STATES PATENTS Number Name Date nected in common with said main cathode and each of said anode and said auxiliary cathode, fizz; 32; ig whereby current flowing 1n the work circuit is 2,213,551 Nelson Sept 3 1940 proportional to the relative adjustments of the 10 control circuits.

EDWARD OSCAR JOHNSON.

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