US2038927A - Vapor filled thermionic tube - Google Patents

Description

April 1936. W. EITEL ET AL 2 ,038,927

VAPOR FILLED THERMIONIC TUBE Ori ginal Filed May 27, 1933 W ll INVENTORS,

WILL/AM W. ITEL.

JACK McCUL LOUGH.

. I I IIIIIIHIIYIIII Patented Apr. 28, 1936 UNITED STATES PATENT OFFICE VAPOR FILLED THERMIONIC TUBE William W. Eitel and Jack McCullough, San Bruno, Calif., assig'nors to Heintz & Kaufman, Ltd., San Francisco, Calif., a corporation of Nevada 4 Claims.

This application is a division of our application, Serial No. 673,234, filed May 27, 1933.

Our invention relates to thermionic tubes having a control electrode, and more particularly to 5 such tubes having a filling of conductive gas, and in which output currents are substantially of a wave form corresponding to that of the input voltages supplied to the control electrode.

Among the objects of our invention are: to

provide a gaseous filling in a thermionic tube while retaining control of the output; to provide a means for increasing the current flow through a thermionic tube; to provide a highly eflicient gas filled amplifier and oscillator tube in which the de-ionization time of the gas is relatively unimportant, and not detrimental to proper operation; to provide a gas filled thermionic tube having portions of differing pressure therein, and to utilize these differences of pressure to provide a more efiicient tube; to provide a means ior preventing a positive ion sheath around a control electrode in a gas filled thermionic tube; and to provide a simple, low impedance, high power amplifier and oscillator tube, and means for gencrating a profuse number of electrons to be used in such a device.

Other objects of our invention will be apparent or will be specifically pointed out in the description forming a part of this specification, but we do not limit ourselves to the embodiment of the invention herein described, as various forms may be adopted within the scope of the claims.

In the drawing which illustrates one preferred form of our invention embodying the methods described herein:

Figure 1 is a longitudinal sectional view of a vertically positioned tube, and a diagram, schematic and reduced to lowest terms, of a circuit in which the device may be utilized.

40 Figure 2 is a cross sectional view taken as indicated by the line 22 in Figure 1.

In high power thermionic tubes of the pure electron discharge type, the cathode is the sole source of electrons, and as such is subject to deterioration, particularly as high anode voltages are customarily necessary due to relatively high resistances between cathode and anode. In addition'to life limitation due to filamentary impairment and eventual breakdown, associated apparatus necessary to produce the needed high anode voltages, together with means to smooth the supply to a substantially pure direct current, is highly expensive, cumbersome, dangerous and inefiicient. Low anode voltages are desirable and 55 relatively easy to obtain.

Considering devices having anode and cathode alone, large reductions in resistance therebetween may be obtained by gas filling the tubes, with resultant and consequent lower anode voltage, and lower anode resistance, due to ionization by 5 impact or collision, the space charge being materially reduced or entirely eliminated. Electron discharge devices of this kind are exemplified by vapor filled rectifiers, particularly those of the mercury vapor type; The gaseous filling'greatly adds to the life of the filament or cathode, particularly when oxide coated heatable conductors are used as a cathode.

Such vapor filled tubes, however, are not subject to electrostatic control of anode current, as are pure electron discharge tubes. Space charge is absent, and a positive ion sheath forms around the control electrode, these factors preventing wave formamplification;

Certainvapo-r tubes have been developed using 20 a type of control, which, however, is that of switching rather than wave form reproduction. In this'type of tube known under the trade-name of Thyratron the anode current may be started by application of a positive potential to the 25 grid, but which cannot be stopped by grid infiuence alone as a sheath, formed from positive ions presentin the ionized gas around the grid structure effectively prevents a negative potential applied to the grid from affecting the anode flow. Such devices are, therefore, not adapted to be used as amplifiers or oscillation generators.

The device employing the methods and construction of our invention is gas filled, and derives from that filling the inherent advantages thereof, the anode flow may be controlled, both started and stopped, in substantial conformity with the voltage applied to a control electrode.

Broadly considered, the novel methods utilized by us to accomplish full grid control in a vapor filled tube comprise one or more of the steps of creating a difference of vapor pressure within the device, providing a conductive path between portions of the gas having different pressures, 45 ionizing the gas in the high pressure portion, abstracting a substantial number of positive ions from the path to leave a remainder composed substantially of electrons, directing the electrons into a low pressure portion of the gas where further ionization by collision is negligible, and controlling and collecting the electrons in .the low pressure portion. We also prefer to make the controlling field subject to a potential gradient such as will tend to prevent the formation of 5 a positive ion sheath around the end of the controlling field.

It has been stated that an envelope containing a condensable gas such as mercury in vapor phase, has a uniform pressure throughout corresponding to the vapor pressure of the coldest portion. Such a statement while generally correct is not specifically true, and does not apply to many envelopes wherein differences of pressure may be developed. An example is the well known mercury vapor vacuum pump wherein mercury in liquid phase is boiled in one portion of a container, cooled and condensed in another, thus building up pressure differences sumcient to cause vapor circulation, and consequent pumping action utilizing the injector principle. This general method of obtaining a pressure difference is used in our invention to create a difference in vapor pressure between the anode end and the cathode end of our envelope. We allow the cathode end to become heated, while cooling the anode end. The difference in pressure may be regulated by the actual temperature difference, and practically all mercury vapor may be removed from the anode end, if desired, by cooling in liquid air.

The apparatus of our invention, in broad terms, may be described as an envelope having therein an anode at one end, a cathode at the other, to provide a path therebetween. A control electrode or grid is placed adjacent the anode between the anode and cathode. The tube is provided with a a gaseous filling, preferably mercury vapor. Means are provided for cooling the anode end of the envelope, the cathode preferably serving to heat the cathode end, although additional heating means may be supplied.

When the anode is energized heavy ionization takes place around the cathode, and means are provided between the cathode and the grid to abstract positive ions from the ionized portion. The remaining electrons pass into the cooled portion of the envelope, and, the mean free path of the gas particles being greater than at the heated end, these electrons do not there cause any substantial ionization. Here they are acted on by the grid, and collected by the anode. The means for collecting the ions is preferably a screen surrounding the cathode and path to the grid, the screen being connected to a source of negative potential.

Referring to the drawing, a cylindrical envelope I is provided with a cathode stem 2 at one end, through which cathode leads 4 are sealed. The leads, extending into the interior of the envelope, support a cathode 5, preferably of oxide coated metallic ribbon. The opposite end of the envelope is provided with an electrode stem 1 through which is sealed a central anode lead 8 and a grid lead 9. .A dummy l0, together with the grid lead 9, support a grid ll of metal gauze l2 mounted on a ring I4, placed between an anode I5 mounted on the anode lead 8, and the cathode. It is preferable that the grid H and the anode be relatively close, leaving a relatively long path between the anode-grid assembly and the cathode. Surrounding the cathode and extending almost to the grid is a mesh screen collector [6 applied in the form of a cylinder to the inner walls of the envelope. It is often preferable to extend the collector to include the grid, and it may, if desired, be shortened to avoid surrounding the cathode. It should, however, be adjacent the portion of the the tube, and when thoroughly freed from gases other than mercury vapor, is sealed from the pumps. Other gases capable of assuming liquid phase within the temperature range available may be used if desired.

Cooling means, in this case a cooling jacket 2!, is then applied to the upper portion of the envelope, surrounding the anode and control electrode and extending to a point above the cathode. Water or other cooling agents may be circulated through the jacket by use of the connections 22.

Figure 1 also shows diagrammatically a circuit in which the tube is operable. A cathode source 23 is connected to the cathode leads 4. A biasing source 24 is connected to one cathode lead and to the screen lead I! to place on the screen a negative potential. An anode source 25 is connected through output posts 26 to the anode lead 8, and one of the cathode leads 4 is connected to the grid lead 9 through input posts 21. As the tube is adapted to be used as either an amplifier or oscillator the remainder of the input and output circuits are not shown, as they will not differ from circuits well known in the art, and as such are no part of our invention.

In operation, the cathode is heated, and cooling liquid circulated through the jacket. The heat of the cathode vaporizes a portion of the mercury and the vapor pressure rises in the lower end of the envelope adjacent the cathode. The cooling jacket, however, causes a condensation to take place before the vapor can reach the anode end of the tube, it being preferable to completely remove all mercury in liquid phase from the upper portion of the tube. A difference in pressure is built up, the pressure being highest adjacent the cathode, and lowest adjacent the anode and control electrode.

In the tube referred to, 500 volts was impressed on the anode, from the anode source 25 through the proper circuit. The region around the cathode became highly ionized, the ionization decreasing towards the anode. 150 volts negative potential was placed on the collector from the biasing source 24, and positive ions from the portion of the path between the oathode and control electrode are attracted to the collector, leaving in addition to the electrons emitted directly from the cathode, those caused by impact in the ionized gas. The augmented stream of electrons passes on to the control electrode through gas having a longer mean free path, collision ionization becomes less and less, more ions are abstracted by the collector, until in the vicinity of the grid, the stream is substantially all electrons, with few ions remaining. This stream passes through the meshes of the grid to the anode, and with other voltages as specified 20 volts negative on the grid will stop the stream, the stream immediately restarting upon removal of the negative charge. Positive grid voltages increase the current to the anode and the characteristic control curve greatly resembles the usual curve of high vacuum tubes.

While it is possible in this manner to create a controllable low resistance path between cathode and anode which will be entirely free from ions in the vicinity of the control electrode and anode, we prefer to utilize an additional feature to prevent a positive ion sheath from forming around the control electrode. We may desire to extend the collector screen to a point closely adjacent the grid. We may in certain tubes enclose the grid as well as the cathode.

With volts negative on the screen and the grid at zero, the screen is 150 volts negative to the grid, tending to draw away from the grid all positive ions approaching it. At 20 volts negative on the grid the screen is still 130 volts negative to the grid, at 20 volts positive on the grid the screen is volts negative to it, so that at all times during the operation of the grid between 20 volts negative and 20 volts positive, there is a gradient between the grid and the screen tending to draw all positive ions approaching the grid to the screen, thus effectively preventing the formation of a positive ion sheath on the grid.

The tube is an effective amplifier and oscillator at high frequencies, the anode resistance is ex-'- ceedingly low due to the electrons caused by impact ionization, wave forms are not substantially distorted, and large power outputs have been obtained without excessive deterioration of the cathode, with low anode voltages.

We claim:

1. A vapor tube comprising an envelope, a cathode at one end of said envelope, an anode and a control electrode-in the other end of said envelope, a filling of conductive gas, a biasing electrode surrounding the path between said cathode and said control electrode, and means for cooling the envelope adjacent said anode, control electrode and a portion of said biasing electrode adjacent said anode and control electrode.

2. A vapor tube comprising a cylindrical envelope, a cathode at one end of said envelope, an anode and a control electrode in the other end of said envelope, said control electrode positioned between said anode and cathode closer to said anode than to said cathode, a cylindrical biasing electrode adjacent the inner wall of said envelope positioned to enclose the greater part of the path between said cathode and said control electrode, and means for cooling the envelope adjacent said anode, said control electrode and a portion of said biasing electrode adjacent said control electrode.

3. A vapor tube comprising a cylindrical envelope, a cathode at one end of said envelope, an anode and a control electrode in the other end of said envelope, said control electrode positioned between said anode and cathode closer to said anode than to said cathode, a cylindrical biasing electrode adjacent the inner wall of said envelope positioned to enclose the cathode and the greater part of the path between said cathode and said control electrode, and means for cooling the envelope adjacent said anode, said control electrode and a portion of said biasing electrode adjacent said control electrode.

4. A vapor tube comprising a vertically positioned cylindrical envelope, a cathode in the lower end of said envelope, an anode in the upper end of said envelope, a control electrode positioned adjacent said anode between said anode and said cathode, a biasing electrode between said control electrode and said cathode, a quantity of mercury in liquid phase in said envelope, and means for cooling the upper part of said envelope to create a lower vapor pressure adjacent said control electrode and said anode than that adjacent said cathode.

WILLIAM W. EITEL. JACK MCCULLOUGH.

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