US2671826A - Current amplifying gas-filled triode under continuous grid control - Google Patents

Description

March 9, 1954 R p BESSQN 2,671,826

CURRENT AMPLIFYING GAS-FILLED TRIODE UNDER CONTINUOUS GRID CONTROL Filed D60. 9, 1952 I l\Lx L TT f Patented Mar. 9, 1954 UNITED STATES PATENT OFFICE CURRENT All/IPLIFYING GAS FILLED TRI ODE UNDER CONTINUOUS GRID CONTROL 10 Claims. 1

It is a well known fact that the anode current in a diode vacuum tube is limited by the space charge produced by the electrons released by the 'thermionically emitting filament and that consequently such a tube can feed a current of only very low intensity when the anode voltage is low.

According to an also well-known fact, the socalled phanotron i. e. a gas-filled diode with a hot cathode does not show this drawback as the ionization of the filling gas neutralizes the space charge and allows the tube to feed an intense current even with a low anode voltage.

According to a further known fact, it is possible to introduce a third electrode or control grid inside a diode vacuum tube so as to obtain a triode vacuum tube in which the anode current is permanently controlled by the biasing voltage applied to the grid. However, such a triode retains the inconveniences of diode vacuum tubes 1. e. a space load, a very low intensity at the anode when the voltage at the anode is low, and a high impedance.

It is also known that if a third electrode or control grid is introduced without any further step being taken inside a gas-filled diode, the tube obtained is a thyratron. The control electrode allows or prevents, according to the bias applied thereto, the discharge of the tube so that the grid operates according to the hit or miss principle. The thyratron or gas-filled triode shows the same advantages as the gas-filled diode as concerns the production of an intense current with a low anode voltage, while it does not show the characteristic property of vacuum triodes, i. e. the possibility of a continuous and gradual control of the anode current by the bias applied to the grid.

My invention has for its object a high power gas-filled triode that shows the advantages of a thyratron as concerns the possibility of feeding an intense current under low anode voltage conditions together with the advantages of a vacuum triode wherein the grid provides a continuous and gradual control.

Further objects and advantages of my invention will appear in the reading of the following description, reference being made to accompanying drawings, wherein:

Fig. 1 is a diagrammatic illustration of my improved discharge tube.

Fig. 2 is a diagrammatic cross-sectional view of the tube showing the detail of the arrangement of its component parts.

Fig. 3 is a wiring diagram showing by way of 2 example a possible application of my improved discharge tube.

In order to allow my invention to be readily understood, I will first disclose how I came to the idea which led to the designing of this tube.

Starting from a diode vacuum tube, I first thought of gradually introducing positive ions between the filament and the anode so as to gradually increase the intensity of the output current through a gradual neutralization of the space charge.

I first disclosed in my prior U. S. Patent No. 2,527,696 dated April 11th, 1945, that the end of a cathodic glow moving along an elongated rod could form a source of positive ions and. that the movement of said source along the rod would be a linear function of the intensity of the discharge passing through the cathodic glow tube.

I have also shown in my French patent application filed on December 13th, 1950, under Prov. No. 601,702, that the idea of a fundamental difference between a thyratron and a vacuum triode was completely erroneous and I have described in said application a gas-filled tube provided with a continuous and gradual control obtained through action of the grid. Such a tube formed a low power tube which I termed a modulating gas-filled tube operated through the biasing of its grid.

Now, according to my present invention, I have designed a high-power gas-filled triode forming the result of my prior investigations and it is characterized chiefly by its operation as disclosed hereinafter.

The low current that is to be amplified shifts a positive source of ions constituted by the end of the cathodic glow moving along an elongated rod; this shifting of the source of positive ions modifies the number of positive ions introduced by said source between the filament and the anode of a gas-filled diode, which leads to a modification in the anodic current of the diode through a neutralization of the space load. Experience shows that, within a large range, this modification is linear. The amplification obtained may be of the order of ten thousand, a variation by one micro-ampere of the current to be amplified producing possibly a modification by ten milliamperes of the current fed by the anode.

To readily ascertain the gist of my invention the following point should be considered: in a conventional vacuum triode, a modification in the voltage of the control grid produces a modification in the intensity of the anode current,

whereby the vacuum triode is responsive to a modification in the grid voltage. In contradistinction, in my improved gas-filled tube, a modification in the intensity of the current in the input circuit produces an amplified modification in the intensity of the current in the anode circuit, so that my said improved discharge tube is responsive to a modification in intensity.

A tube, according to my invention, is illustrated diagrammatically in Fig. 1 and it includes chiefiy, inside a closed chamber V, filled with a rare gas or with a mixture of such a gas with a metal vapor: a thermo-emissive filament F adapted to produce through its thermionic emission an electronic current of high intensity, an anode P located at a small distance from the filament to form a diode therewith and brought to a positive potential with reference to said filament, said potential being however sufficiently low for the electrons emitted by the filament to be incapable of acquiring inside the filamentanode space an energy sufficient for the ionization of the gas filling the tube, a source of positive ions constituted by the end of a negative glow the length of which may vary over an elongated rod C forming a secondary cold cathode, a secondary anode A providing for the production of a glow discharge between said anode A and said cathode C and lastly an auxiliary electrode G forming the control grid that is located inside a lateral recess of the tube and that allows modifying the intensity of the glow discharge and consequently the length of the cathodic glow extending over the cold secondary cathode rod C and finally the number of positive ions introduced between the filament F and the anode P associated therewith in the diode.

The execution of my improved tube does not lead to any difiiculty and when produced on an industrial scale it assumes the outer shape of a wireless set tube of a somewhat increased length and provided with two horn-shaped projections; a cross-section thereof executed near its foot on the secondary cathode side shows the inner arrangement of the elements as executed in practice (Fig. 2).

The anode P is made of pure nickel and assumes the shape of a half cylinder and the filament F is located along the axis of said halfcylinder, while the secondary anode A is constituted by an iron or nickel rod having a diameter of about 3 to 4 millimeters and a length of about 2 to 4 centimeters.

The cathode C is constituted by a nickel rod,

possibly carrying a thermo-emissive coat and the I diameter of which is equal to about 1 mm. while its length is equal to centimeters or thereabouts. The electrode forming the control grid G is about 1 cm. and it is housed in a radial recess of the tube on the outside of the path of the glow discharge as illustrated in Fig. 1, said recess registering with a point located between the secondary anode and cold cathode and slightly nearer the cathode.

The filling of the tube chamber is constituted by neon with the addition of a very small amount or traces of argon under a pressure of 1 to 60 mm. of mercury. In the case of an experimental tube of which I will disclose hereinafter the performances, the pressure applied was that of a mercury column of 4 mm. In order to obtain a response of the tube for high frequency currents, the filling should be constituted by pure helium and, in contradistinction, in the case of currents at industrial frequency, the filling should be constituted by a rare gas with the addition of traces of mercury vapor.

The formation of the tube includes the heating to 300 C. of the tube inside a kiln, the exhaust of the gases from the anode, the cathode and the control electrode by means of a glow discharge executed under reduced vacuum, the obtention of a high vacuum, the exhaust of the gases from the filament by means of a direct heating obtained through the passage of the current, the filling with rare gas after the cooling under complete vacuum, and finally the separation of the finished tube from the blank through the melting of the tail end by means of a blow pipe.

The operation of the tube will be readily ascertained upon inspection of Fig. 3, which shows an amplifying wiring diagram for sound picture projection, in which the signal to be amplified is constituted by the current from a sound reading photo-cell K, that is to feed, after amplification, the loud speaker L.

The movable coil of this loud speaker forming the load impedance is inserted in series with a comparatively low source of voltage SI (12 to 18 v. for instance) inserted between the anode P and the filament F of the diode, the filament being heated by a source S2 of say 4 volts. A supply S3 feeding a voltage of 200 to 300 volts produces a permanent glow discharge between the secondary anode A and the cathode C, while a resistance R of the order of 50,000 ohms limits the intensity of the discharge current to a value of the order of 1 milliampere; a cathodic glow the length of which is about 6 to 8 cm. extends then over the cathode.

A potentiometer Q is connected across the terminals of the voltage supply S3 and the photocell K that serves for sound reading is inserted between the control grid G of the tube V and the slider q of the potentiometer.

The grid G is thus brought to a potential intermediate between the potential of the cathode C, on one hand, and that of the anode A, on the other hand, and an adjustable current of a few microamperes flows through the circuit KGAq. As a modification in the illumination of the photo-cell K corresponds to a modification in the intensity of the photoelectric current by say 1 microampere, will produce a modification of the order of microamperes in the glow discharge circuit ACRS3. This modification in the intensity of the glow discharge current leads to a corresponding modification in the length of the cathode glow; said cathode glow acts as a source of positive ions for the surrounding space and chiefly for the space comprised between the filament F and the anode P of the diode section of the tube and consequently this leads to a modification in the number of positive ions introduced inside said space; consequently this will lead to a modification ranging between 10 and 100 milliamperes in the output circuit PFSIL of the diode i. e. a total intensity amplification factor comprised between 10,000 and 100,000. The modulated power fed to the loud-speaker is higher than 1 watt and the amplifier described, including merely the tube according to my invention, is sufiicient for the reproduction of sound in an average-sized hall.

In order to readily ascertain the operation and the nature of the amplifier tube according to my invention and to distinguish it from the usual amplifier tubes, I wish to insist again on the fact that the output signal due to the modifications in the apparent resistance or in the admittance of the diode P-F' are produced the case of my improved tubeby the modifications in the grid current, i. e. in the intensity of the auxiliary discharge produced between the control electrade or grid G and, the anode A. This discharge is essentially diflerent from the glow discharge between the anode A and the cathode C by reason of its showing none of the features of a disruptive discharge and consequently its intensity, which is of the order of a few microampercs, remains directly controlled by the impedance.- of the circuit. The permanency of said auxiliary discharge implies furthermore that the grid G is brought to a potential intermediate between the cathode and anode potentials; said grid is thus. submitted to a positive bias with reference to the cathode, of the order of say 190 volts for instance. If said biasing were to drop underneath a predetermined limit, the auxiliary discharge would assume the character of a disruptive discharge and the gridwould carry a cathode glow and lose the possibility of controlling the operation of the tube.

In other words, the grid seems to act as a secondary cathode emittin lectrons which deflect those emitted by the cathode C and produce thus a modification in the admittance of the space between C and A, together with a modification in the length of the cathode glow ex-- tending over C. For instance, for a potential of 300 volts on the anode A with reference to the cathode C, the grid retains its control action within a range of potentials ranging between about 30 and 200 volts, the exact extent of said range depending on the admittance of the gridcathode input circuit and also on the nature of the metal constituting the grid and on the area of the latter.

As the grid circuit includes the source of energy required for its biasing, its control may be obtained very simply by inserting in. series in said circuit an element assuming a high resistance varying under the action of the phenomenon to be amplified; this is the case of the diagram shown in Fig. 3 where this element isconstituted by the photo-cell K, while the magnitude of the phenomenon to be amplified is constituted by the varying illumination of its cathode. This may be generalized readily and for instance in the case where the magnitude to be amplified is an electric voltage, it is possible to resort to a pro-amplifier tube such as a pentode or a semiconductive element of the transistor type, the

admittance of which is very low and may be controlled by said voltage to be amplified.

In other words, an amplifier according to my invention provides in response to the modifications brought to a very low admittance inserted in its grid circuit or primary circuit, considerably amplified modifications in the higher admittance of the diode P-F inserted in its output or tertiary circuit, said amplification being performed through the agency of an intermediate or secondary circuit of intermediate admittance constituted by the luminescent discharge between the secondary anode A and the cold, elongated secondary cathode C.

Obviously, the filament F may be replaced by a thermionic electron emitting cathode that is heated indirectly.

What I claim is:

1. An arrangement for amplifying electric currents comprising a gas-filled tube, a thermoemitting cathode and an anode forming there- 6 with. a diode carried inside said tube, glow discharge means carried inside the tube and including a cold elongated cathode one end of which extends into the space separating the cathode from the anode of the diode and a secondary electrode at a distance from said diode space, means including a supply of direct current voltage and a resistance and adapted to produce between said cold cathode and secondary electrode: a glow discharge forming. a glow of a predetermined length on said cold cathode, means controlled by the current to be amplified and adapted to control the length of said glow on the cathode to make the latter vary in accordance with the variations of said current and an output circuit including in series with the diode a source of low voltage and a load impedance fed by the amplified current.

2 An amplifier tube comprising an elongated gas-filled closed chamber, an elongated rodshaped cold cathode extending longitudinally through said chamber up to a point short of one end thereof, a secondary anode facing. the end or the cold cathode at last mentioned and of the chamber, a thermo-emitting cathode housed in the section of the chamber that: is opposed to said first mentioned end, a diode anode located in front of and at a small distance from said thermo-emitting cathode, control means producing an electric field in the section or the chamber comprising the space separating the secondary anode from the cold cathode to produce a glow discharge over the cold cathode, said glow discharge forming a source of positive ions adapted to increase the intensity of the output discharge betweenthe thermo-emitting cathode and the anode of the diode and means acting on said control means to modify the value of said electric field and consequently the intensity of the glow discharge and, thereby, the intensity of the output discharge.

3.. An amplifier tube comprising an elongated gas-filled closed chamber, an elongated rodshaped cold cathode extending longitudinally through said chamber up to a point short of one end thereof, a. secondary anode facing the end of the cold cathode at last mentioned end of the chamber, a thermo-emitting cathode housed in the section of the chamber that is opposed to said first mentioned end, a diode anode located in front of and at a small distance from said thermo-ernitting cathode, a control electrode carried inside the tube laterally of the glow discharge and producing an electric field in the section of the chamber comprising the space separating the secondary anode from the cold cathode to produce a glow discharge over the cold cathode, said glow discharge forming a source of positive ions adapted to increase the intensity of the output discharge between the thermoemitting cathode and the anode of the diode and means acting on said control electrode to modify the value of said electric field and consequently the intensity of the glow discharge and thereby, the intensity of the output discharge.

4. An amplifier tube comprising an elongated gas-filled closed chamber, including a lateral proiecting section, an elongated rod-shaped cold cathode extending longitudinally through said chamber up to. a point short of one end thereof, a secondary anode facing the end of the cold cathode at last mentioned end of the chamber, a thermo-emitting cathode housed in the section of the chamber that is opposed to said first mentioned end, a diode anode located in front of and at a small distance from said thermo-emitting cathode, a control electrode carried inside the recess in the chamber, the gap between the secondary anode and the cold cathode lying in substantial lateral register with the recess in the tube and producing an electric field in the section of the chamber comprising the space separating the secondary anode from the cold cathode to produce a glow discharge over the cold cathode, said glow discharge forming a, source of positive ions adapted to increase the intensity of the output discharge between the thermoemitting cathode and the anode of the diode and means acting on said control electrode to modify the value of said electric field and consequently, the intensity of the glow discharge and thereby the intensity of the output discharge.

5. An electric amplifier comprising a gas-filled tube, a thermo-emitting cathode inside said tube,

an anode located at a small distance from said cathode and forming a diode therewith, means for biasing said anode to a positive potential with reference to the thermo-emitting cathode to constrain the anode to collect all the electrons emitted by the cathode before the discharge constituted by said electrons has acquired a sufficient momentum for it to ionize the gas filling the tube, an elongated rod-shaped cold cathode extending transversely through the diode space between the thermo-emitting cathode and the associated anode, said cold cathode extending over a substantial fraction of its length outside said diode space, a secondary anode located at a distance from the end of the cold cathode furthest removed from said diode space, means for producing between the sec ondary anode and the cold cathode, a glow discharge extending over a fraction of the length of the cold cathode and control means adapted to modify said fraction of the length of the cold cathode covered b the glow and to modify thereby the intensity of the discharge between the cathode and anode forming the diode.

6. An electric amplifier comprising a gas-filled tube, a thermo-emitting cathode inside said tube, an anode located at a small distance from said 'cathode and forming a diode therewith, means for biasing said anode to a positive potential with reference to the thermo-emitting cathode to constrain the anode to collect all the electrons emitted by the cathode before the discharge constituted by said electrons has acquired a sufficient momentum for it to ionize the gas filling the tube, an elongated rod-shaped cold cathode extending transversely through the diode space between the thermo-emitting cathode and the associated anode, said cold cathode extending over a substantial fraction of its length outside said diode space, a secondary anode located at a distance from the end of the cold cathode furthest removed from said diode space, means for producing between the secondary anode and the cold cathode, a glow discharge extending over a fraction of the length of the cold cathode and a control electrode located to one side of the glow discharge and at a distance therefrom in side said tube, said control electrode being adapted to modify said fraction of the length of the cold cathode covered by the glow and to modify thereby the intensity of the discharge between the cathode and anode forming the diode.

7. An electric amplifier system including in combination a gas-filled amplifier tube and the :following partsenclosed inside said tube: a

thermo-emitting cathode, an anode located at a small distance from said cathode and forming a diode therewith, an elongated rod-shaped cold cathode extending up to a point at a distance from said diode cathode and anode and a sec-' ondary anode located in proximity with last mentioned point of the cold cathode, an output circuit having a low impedance and including a source of voltage and a load resistance, said output circuit passing through the diode, an intermediate circuit comprising a source of voltage and a resistance connected between the secondary anode and the cold cathode and a high impedance input circuit to which the signal to be amplified is applied, said input circuit including means for controlling the intensity of the glow discharge between the secondary anode and the cold cathode.

8. An amplifier system comprising an elongated gas-filled tube including a lateral recess. a cold cathode assuming the shape of a long rod extending between a terminal section of the tube and a point in proximity with the opposite terminal section and in register with the recess, a thermo-emitting cathode and an anode positioned in front of said last mentioned cathode forming a diode therewith in the first terminal section of the tube, a secondary anode housed in the last mentioned terminal section of the tube, a control electrode housed in the lateral recess of the tube, an adjustable resistance and a source of voltage inserted between the secondary anode and the cold cathode to produce between the latter a glow discharge forming a glow over a fraction of the length of said cold cathode, potentiometric means inserted in parallel with said source of voltage and including a slider adapted to be brought to a potential intermediate between that of the cold cathode and that of the anode, high impedance means varying with the signal to be amplified and inserted between said slider and the control electrode and an output circuit including in series between the diode anode and cathode a source of voltage and a load impedance.

9. An electric amplifier including in combination a gas-filled tube, a thermo-emitting cathode inside said tube, an anode forming with said cathode a diode, providing a non-disruptive discharge path between said cathode and anode, an elongated rod-shaped cathode and a secondary anode carried inside the said tube and separated by a gap for the production of a glow discharge, the glow of said discharge extending over a fraction of the length of the cold cathode, a control electrode located toone side of said glow discharge gap, a high admittance output circuit including a source of low voltage in which said diode discharge path is inserted in series, an intermediate circuit mounted across the outer terminals of the secondary anode, on one hand, and of the cold cathode on the other, said intermediate circuit including a source of voltage and a resistance, and a low admittance input circuit including means for bringing said control electrode to a potential intermediate between that of the cold cathode and that of the secondary anode to make the modifications in the low admittance of the input circuit produce amplified modifications in the admittance of the discharge between the heat-emitting cathode and associated anode in the input circuit.

10. An arrangement for amplifying electric currents comprising a gas-filled tube, a thermoemitting cathode and an anode forming therewith a diode carried inside said tube, glow discharge means carried inside the tube and including a cold elongated cathode one end of which extends into the space separating the cathode from the anode of the diode and a secondary electrode at a distance from said diode space, means including a supply of direct current voltage and a resistance and adapted to produce between said cold cathode and secondary electrode a glow discharge forming a glow of a predetermined length on said cold cathode, an auxiliary grid fed by the current to be amplified and adapted to make the number of positive ions produced by said cathode glow vary in accordance with the variations of said current and an 10 output circuit including in series with the diode a source of low voltage and a load impedance fed by the amplified current.

RAOUL PAUL BESSON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,292,382 Le Van Aug. 11, 1942 2,428,048 Stutsman Sept. 30, 1947 2,578,571 Meier Dec. 11, 1951 2,611,090 Wolff Sept. 16, 1952 2,631,261 Hough Mari 10, 1953

Images