US2195505A - Electron discharge device - Google Patents

Description

April 1940- B. J. THO'MPSON. 2,195,505

ELECTRON DISCHARGE D EVICE Filed Nov. 27, 1936 INVENTOR BROWDER J.THOMPSON ATTORNEY Patented Apr. 2, 1940 I UNITED STATE ELECTRON nrsonmca p'EVIoE 1 Browder J. Thompson,

Basking'Ridge, N. J.,

' signor, by mesne assignments, toRadio Colporation of America, poration' of Delaware New'York, N. Y., a cor-Y- Application November 27, 1936, Serial No. 113,096 I 10 Claims.

My invention relates to electron discharge devices, more particularly" to grid controlled gas tubes.

In the conventional grid vacuumtubes provided with a thermionic cathode, control grid and anode, the space charge which builds up around the cathodemakes necessary the use of comparatively high voltages, such as 100 volts or more, for obtaining current sumciently large for practical purposes. It is also necessary to use comparatively large grid voltage swings to produce usable variations in the output of the tube. Thus, in the conventional high vacuum tubes comparatively large transconductances are not easily obtainable nor can large anode currents be obtained with small anode voltages. It has been recognized that by introducing a gas in a tube and ionizing the gas the space charge around the cathode could be neutralized and thus large anode currents obtained with the usual anode voltages. However, inthe conventional grid controlled tube containing gas, ionization of the gas causes the control grid to. lose its control of the electron stream so that while initiation of ionization can be controlled the current cannot be controlled by the control electrode after ionization takes place. Furthermore, in these types of tubes comparatively high voltages, much above ionization voltages, are applied between the anode and cathode to cause a gas discharge between the anode and the cathode. Thus while comparatively high currents can be obtained the loss of grid control and the necessity for high anode-cathode voltages limits the application of this type of tube and prevents its use in conventional radio circuits. g It is, therefore, the principal object of my invention to provide an electron discharge device having a high transconductance and in which large anode currents can be obtained with very small anode voltages and small grid voltage swings. More specifically itis an object of my invention to provide such a tube dependent upon gas ionization for its operation but which nevertheless can be continuously grid controlled.

In accordance with my invention I produce such a tube by introducing gas at a low pressure into an envelope containing the electrodes and ionizing only the space adjacent the cathode to neutralize thespace charge and thus make available a large number of electrons. I can then apply only a very small voltage of the order of 2 to 10 volts considerably below ionizing voltage between the anode and cathode to obtain a comparatively large anode current. The flow c1. zen-21y l I I t I of electrons .from the cathode to the anode can then be continuously controlled by a grid to which is applied comparatively small voltage swings, inasmuch as there is no gaseous discharge between the main cathode and anode. 5" Toy produce the ionizationiof the gas around the cathode I may employ an auxiliary cathode and establish a discharge between the auxiliary cathode and the main cathode, although the same results could be accomplished by estab- 10, lishinga discharge between the auxiliary cathode and anotherelectrode, the main cathode being positioned within the vicinity of the discharge path. In-order to confine the ions to the space around the main cathode, which is desirable,

Isurround the main cathode with a cage having foraminous portions through which the electrons may move and connect the cage to the main cathode. In one preferred embodiment of my invention the auxiliary cathode and the main 20 cathode may be placed within the cage and the 'control'grid in an opening in the cage. In another arrangement the auxiliary cathode alone or with the control electrode may be placed outside of the cage.

while the electrons can reach the anode, the ions are confined to the space around the cathode and are prevented from causing a complete ionization of the gas within the tube or of combining at the surfaces of the other electrodes 30.

or on the tube envelope wall and thus losing their neutralizing ability.

v The novel features which I believe to be characteristic of my invention are set forth with par ticularity in the appended claims, but the inven- 35 tion itself will best beundrstood by reference to the following description taken in connection with the accompanying drawing in which Figure 1 is a schematic diagram of a tube embodyingone form of my invention and associated cir- '40 cult, Figure 2 is a schematic view of a modification of the tube shown in Figure 1 and its associated circuit, and Figure 3 is a schematic View ofya still further modification of the tube shown in Figure 1. I v

In Figure 1 the envelope II] which may contain a gas for example at a low pressure has mounted within it the main thermionic cathode i l, preferably a filament, and an auxiliary cathode [2." During operation a gaseous dis-' 50 charge is established between these two electrodes to provide ions in the space particularly around the cathode ll. Surrounding'the cathodes II and I2 is a conducting cage member havingthe bottom portion l3, preferably of solid By the above arrangements 25 I the cage preferably comprises a screen I I having at its upper side an opening at the edge of which is supported an insulating ring I8. This insulating ring It in turn supports the control grid It in the opening to completely enclose the cathodes. An anode 20 is supported opposite the grid I9. The cathode filaments are heated from the source of voltage 2I and 22 and cathode II maintained at positive potential with respect to cathode I2 by means of voltage supply 23, the value of which is sufliciently high to provide a gaseous discharge between cathodes II and I2 to ionize the space around the cathodes. The input circuit voltage is supplied from a source 24 between the control grid I9 and the cathode l l, the grid being negatively biased by means of battery 25. The output circuit includesa load 26 connected to the output of anode 20, the load voltage being supplied by means of source of low voltage 2? which is preferably less than that necessary to establish ionization between the cathodes and anode 29. Because the ions'generated within the cage cannot leave the cage, only the space within the cage is ionized. The ions, therefore, are used only to neutralize the space charge around the cathodes, permitting a copious flow of electrons to the anode. Since only electrons leave this cage to anode 29 and no appreciable ionization takes place between grid and anode the control grid I9 maintains control over the flow of electrons from the oathodes II and I 2 to the anode 20. There is thus no loss of ions by recombination at surfaces of, for example, the anode and the walls of the tube and a very efficient tube is thereby produced having a high mutual conductance and a low anode drop. Very small positive voltages on the grid permit large numbers of electrons to move to the anode, since largenumbers of electrons released by ionization are close to the grid in the ionized space within the cage.

The gas which may be used within the envelope may be of any of the inert gases, such as neon, helium or argon, or caesium vapor alone or in combination with any of the gases mentioned at relatively low pressures. However, the range of pressure is not critical and may vary from .01 of a micron to 200 microns or more. When using helium I have found that a voltage of approximately 30 volts between the cathodes is sufiicient to produce ionization and that a voltage from 2 to 10 volts between the main cathode and the anode is satisfactory in the load circuit. With this arrangement very small grid voltages and currents of a few milliampereswill control large anode currents of th order of l or 2 amperes. Such tubes can be directly connected to loud speakers.

To further increase the ion life, the modification shown in Figure 2 may be employed. The envelope 359 contains the main cothode 3i surrounded by cage 33, which is electrically connected to one of the legs of the cathode filament in uiatecl from the other by bushing 32. Insulating bushings 32 and 32 may be provided to insulate the cathode leads outside of the cage and thusprevent discharge between these'legs and the auxiliary cathode. The cage has on one side an opening 3t covered with mesh and'at the top an" opening forthe contro-l grid' iii-supported in an insulating ring 36 in the opening in the cage. The auxiliary cathode 31 may be mounted outside of the cage in front of the opening 34, the source of voltages 38 and 39 providing the heating current and the source of voltage 40 providing the voltage necessary for producing a gaseous discharge between the two cathodes. The cathode 3'! is preferably placed close to the shield 33 so that the electrons do not attain sufiicient velocity to cause ionization of the gas outside the cage. The input voltage is applied from the source 4I between the grid 35 and the main cathode 3I. A grid biasing battery 42 may be used. The anode 43 is connected to the load 4'3 and the source of anode voltage 45 of a value considerably less than necessary to cause ionization between cathode and anode.

In Figurefl I show a form of electron current multiplier making use of my invention. Here the envelope contains the thermionic cathode 5| surrounded by a cage 52 electrically connected to one of the legs of the cathode. The other leg is insulated by means of the insulating sleeve 55 which withthe insulating sleeve 58 also protects the-cathode leads extending outside of the cage to prevent undesirable discharges between these leads and other electrodes Within the tube. This cage may be provided with foraminous portions 53 and or openings covered with mesh material through which electrons may pass. An auxiliary cathode 5? is mounted outside of the cage and close to the forarninous portion 53. A control grid 58 is provided between the cage 51 and the ioralninous portion 53. An output anode 59 is positioned opposite the other foraminous portion 54. The heating voltages for the cathodes 5i and 5'! are furnished by the voltage suppliers lit and El, the cathode 5i being maintained at a higher potential with respect to the cathode 5'! by means of the source of voltage 62 which has a value at least as great as that necessary to produce ionization between the two cathodes. An inputcircuit 63 is connected between the control grid 58 and the main cathode BI. The output circuit connected to the anode 59 includes the load 54 and the anode voltage supply 65 which is less than that necessary to produce ionization between the cathodes and the anode.

In operation of the tube when a voltage is applied to the grid 58 so that electrons move from the cathode 57 to cathode 5! to ionize the space around the cathode 5Ielectrons in proportion are released from the space around the cathode 5i and pass through the ioraminous portion 51 of the cage to the anode 59. The degree of ionization and hence the number of electrons from the cathode 55 to anode 59 is dependent upon the voltage applied to the control grid 58, that is the higher the voltage on control grid 58 the greater the ionization in the space surrounding the oathode 5i andthe larger the number of electrons moving to the anode 59.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for which my invention maybe employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that manyvariations may be made in the particular structure used and the purpose for which it is employed without departing frorn the scope of my invention as set forth in the appended claims.

What I claim as new is;

J rin-electron-discharge device having an enanode for receiving electrons from said cathodes imionic cathode electrode within said envelope for emitting electrons, a cage surrounding the thermionic cathode and electrically connected to said cathode and having openings through which electrons can pass,an anode electrode for receiving electrons fromsaid cathode electrode, a second cathode for supplying electrons to ionize only the space surrounding said thermionic cathode, means for applying a voltage above ionization voltage between said second cathode and one of said other electrodes, a grid insulatingly supported within the opening in the cage for continuously controlling the flow of electrons to said anode, an input circuit connected between said thermionic cathode electrode and said grid, and an output circuit connected between said thermionic cathode electrode and said anode electrode and including a source of voltage substantially less than that required to produce a gaseous discharge between said .thermionic cathode electrode and said anode electrode. 2. An electron discharge device having an envelope containing a gas at a low pressure, a ther- ,mionic cathode within said envelope for emitting electrons, a second thermionic cathode within said envelope cooperating with said first thermionic. cathode during operation of the electron discharge device for producing ions in the space surrounding said first thermionic cathode, an

and means within said envelope and positioned between the cathodes for controlling the dischargeirom the second thermionic cathode to said first thermionic cathode to control the ionization around said first thermionic cathode, and the flow of electrons to said anode.

3. An electron discharge device having an envelope containing agas at a low pressure, a thermionic cathode within said envelope for emitting electrons, a second cathode withinsaid envelope cooperating with said thermionic cathode during ope-ration of said-electron discharge device for producing ionization in the space surrounding said thermionic cathode, a conducting cage surrounding said cathodes and electrically connected to the thermionic cathode and having foraminous portions through which electrons can pass, an anode outside said cage for receiving electrons from said thermionic cathode, and a control grid insulatingly supported'by said cage for controlling the flow of electrons from said thermionic cathode to said anode.

4. An electron discharge device having an envelope containing a gas at a low pressure, a thermionic cathode within said envelope for emitting electrons, a conducting cage surrounding and electrically connected to said cathode and having forarninous portions through which electrons can pass, a second cathode within said envelope and a source of voltage connected between said cathodes high enough to cause ionization in the ing and electrically connected to said cathode, an i opening in said cage, a control grid insulatingly supportedin said opening to close saidopening, an anode opposite said opening and means for producing ionization within said cage to neutralize any space charge around said cathode Whensaid tube is in operation. 3

6. An electron discharge device having an envelope containing a gas, a thermionic cathode within said envelope for furnishing electrons, a cage surrounding and electrically connected to said cathode, an opening in said cage, a grid in,-

sulatingly supported in said opening to close said opening, an anode opposite said opening for receiving electrons from said cathode, and a second oathodewithin saidenvelope.

'7. An electrondischarge device having an envelope containing a gas, a pair of spaced therv mionic, cathodes within said envelope, a metallic cage surrounding said cathodes, said cage being electrically connected to one of said cathodes, an opening in said cage, a control grid means, for insulatingly supporting the control rid within said opening to close said opening and an anode positioned opposite said opening a control electrode insulatingly supported-within said opening to close said opening, and an anode opposite said opening and outside of said cage,

and a second cathode within said cage, means for applying a voltage between said cathodes suificient to ionize the gas surrounding said cathodes, and other means for applying a voltage between saidcathodes within said cage andsaid anode for producing a flow of electrons from'the space within said cage to said anode, and an input circuit connected between said control electrode and said cathodes.

9. An electron discharge device having an envelope containing a gas at a low pressure, a thermionic cathode Withinsaid envelope for emitting electrons, a conducting cage v surrounding and electrically connected to said cathode and having foraminous portions through which electronscan pass, a secondcathode within" said envelope out- 1 side of said cage and opposite one of said forarninous portions, and a grid positioned'loetweensaid second cathode and the foraminous portion of said cage, and an anode outside of said cage opposite another of said foraminous, portions of said cage.

10. An electron discharge device having an envelope containing a gas at a low pressure,- a thermionic cathode within said envelope for emitting,

electrons, a conducting cage surrounding said cathode and electrically connected to said cathode and provided with foraminous portions through which electrons can pass, a second cathode within'said envelope cooperating with the thermionic "cathode during operation of the electron discharge device for producing ions in the space surrounding said, thermionic cathode, an anode positioned on the outside of said cage and positioned opposite a ioraminous portion for receiving electrons from the space surrounding the thermionic cathode, and a'control grid for concathode and the anode.

.trOHing the discharge between the thermionic

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