US2189358A - Diode oscillator tube construction - Google Patents

Description

Feb, 6, 1940. P. T. FARNSWORTH I DIODE QSCILLATOR TUBE CONSTRUCTION Filed March 22, 1937 INVENTOR, PH/LO 7: FARNSWORTH.

A TTORNEYS.

Patented Feb. 6, i940 U TE ,STATES Philo T. Farnsworth,

1 v I PATENT OFFlRCEi? i] I I 2,189,358 r I I d I a mom:- OSCILLATOR TUBE coNs'rRUow TION "Springfield Township,

Montgomery County, Pa., assignor, by mcsne assignments,

of Delaware A Application March 22, 8 Claims. (01. 250-174) .The tube structure hereinto be describedop crates broadly in accordance with the method described and claimed in myprior application,

Serial No. 692,585,- filed October 7, 1933, since matured into United States Patent No. 2,071,515,

patented February 23, 1937. The present appli-- cation is a continuation in part of my prior ape plication, Serial No. 733,837, filed July 5,- 1934,

since matured into United StatesPatent No.

- 2,071,516, patented February 23,1937, and, in addition, is a continuation'in part of my co- .pendingapplication, Serial No. 51,042, filed January 27, 1936, since maturedintoUnited. States Patent No, 2,137,528, patented November 22, 1938.-

The latter patent refers to various circuitsutilized in combination with the diode multiplier tube herein tobe described and claimed, whereas the present application. refers solely. to the tube structure.

Among the objects of. my invention are: To

provide an electron..multiplier tube having a cathode system wherein electrons emitted from 30 one area thereof will impact an opposite area; to provide an electron multiplier tub e havinga fundamental diode structure which canbe utilizedfor amplification or oscillation generation; to provide a diodestructure capable of self-oscillation when the diode electrodesareproperly energized and connected by aeresonant circuit; to provide a simple and efficient electrode structure capable of producing electron multiplication of a not limitmyself to the embodiment of the invention herein described, as various forms may be adopted within the scope of the claims.

, Referring to the drawing; i

, Figure 1 is ase'ctionalview, partly schematized, of a diode multiplier embodying my invention. FigureZ is a cross-sectional View of the pre-. ferred form Ofll'lVBlllliOlil shown in Figure Ltaken 6Q as indicated by the line 2- 2.v

I y to Farnsworth Television & Radio Corporation, Dover, DeL, a corporation high orderof magnitude; to provideanelectron multiplier tube having electrodes capable of oretion forming a part of this specification, but I do 1937, Serial bid-132,327 I therein claimed, and is fundamentally a diode. l9

, Oscillation generators operating by means of electron stream control,-hitherto known in the art, have all comprised tubes havingat least.

three electrodes. In. other words, prior oscilla? tion generators and thermionic amplifiers vhave, lg as fundamental structure, first, a hot cathode emitting a copious supply of electrons,v when heated; second, acollecting anodeto which the emitted electrons travel; and third, a control electrode, so positioned as to regulate the numberuof electrons reachingthe anode, in accordance with a potential imposed thereon. It is well known in the-art that such a triode is anamplifier, and, in consequence, ifenergy be fed back from the output or anode circuit to the control electrode o circuit in'proper phase, the triode becomeswan oscillation generator. vInasmuch as the genera: tion of oscillations. by this triode is dependent upon thereaction between the input and output circuits and the transfer of energy therebetween, 56 it is obvious that any diode, to gene'rateselfi oscillations, must naturally operate. onan'enf tirely differentprincipler Such a principle was discovered and set forth in my; Unitedjstates Patent No. 2,137,528, and maybe re-stated here .in simple form, as follows: If an. electron beacceIeratedtoward a surface capable of producing secondary electrons uponimpact with said sure face at a ratio greater than unity; electron multi plication will occur, and if repeated similar inn pacts are made, seriatim electron multiplication of exceptionally high value may be secured be: fore saturation limits the action. I have found thatsuch repeated impacts maytake placeli'n a properly arranged diode structure comprising only acathode sensitized to produce. secondary electrons at the required ratio and an accelerate ing anode so positioned as to direct the'electrons into ,the proper paths between impacts. It was further found and described in my United States Patent No. 2,137,528, of which .the present ap cation is a continuation in part,jthat, sucl a H odewill become an efiicient oscillation generator with ,only the connection of a resonant circuit between anode andv cathode, together with ,a steady source of potential imposed upon vthe an:- ode withrelation tothe cathode I I am well aware, or the fact that'th'ereare many diodes existing in the prior art, ,beginning with theelectron valve of Fleming and conting uing to the present day, either in unchanged form, as in hot-cathode rectifier tubes, well known in the art, or, for example, as photoelectric tubes wherein the basic structure is a photoelectric cathode and an anode positioned to collect electrons emitted from the photoelectric cathode under the influence of light or radiant frequencies closely allied thereto. However, none of these prior-art diodes are capable of oscillation generation. The main distinction between my present invention and prior diodes is in the arrangement and structure of the anode with respect to the sensitized surface of an unheated cathode. While such an arrangement of structure may at first glance seem only a trivial departure from the prior art, nevertheless no one has hitherto succeeded in making any diode structure that will self-oscillate. It therefore is obvious that the arrangement of anode structure with relation to an unheated cathode, as herein described and claimed, represents a distinct advance in the art, inasmuch as a new and totally unexpected result has been obtained, namely, a structure which simply needs a steady difference of potential between the anode and cathode and a regulatory resonant circuit to become a highly efficient scillation generator of high power.

The tubes illustrated in the drawing will now be referred to in order that the principles underlying the design necessary for the production of self-oscillations in the diode may be more fully understood.

Referring to Figures 1 and 2, a tubular envelope l is provided at each end with reentrant stems 2 and 3. At one end. stem 2 supports a hollow apertured anode formed, in this embodi ment, of fine refractory wire 4, wound as a spiral on upright supports 5, the wire being welded to the supports at each contact therewith. Surrounding the anode and coaxial therewith is a cylindrical cathode 6, preferably unperforated, and supported by leads 1 from stem 3. Anode lead 8 and cathode lead 9 pass through their respective stems so that outside electrical connection can be made. It is obvious, in this regard, that the anode and cathode may be supported in any convenient manner well known in the art.

The inner surface It of the cathode cylinder 6 may either be treated so that secondary electrons will be emitted therefrom at a ratio greater than unity when impacted by electrons traveling at a proper velocity, or the entire cathode may be made of a material which, itself, has such a secondary-emission characteristic, and I deem the two to be full equivalents. For example, cathode may be made of aluminum. Cathode 6 may also be made of a barium nickel alloy. treated during the processing of the tube so that the inner surface H! is sensitive to electron impact to produce secondary electrons. Or, ma terial having a high secondary emissivity may be evaporated by auxiliary containers within the tube and deposited on the inner surface I B. Barium is a good example of such a material. However, I have found that the maximum sensitivity may be obtained by making cathode 6 of silver. oxidizing it, and condensing caesium thereon until maximum secondary electron sensitivity is obtained. 1 have found that this sensitivity to electron impact does not occur at the point where maximum photoelectric response is obtained, but actually occurs, both with barium and caesium, at the point where maximum thermionic emission occurs, and this point may be found during the processing of the tube by heating the entire tube in an oven and checking the thermionic emission which, with such materials of low work function, will occur far below the red temperature. I wish it to be distinctly understood, however, that the tube structure does not require exceptionally high sensitivity to electron impact to be operative, either as an amplifier or oscillation generator, because of the fact that as the output of the tube is based on multiple impacts to produce a large number of secondaries, an extra impact or two will make up for a decrease in sensitivity of the cathode surface l0.

After the cathode surface has been sensitized or otherwise treated, the tube is evacuated to a high degree and sealed off the pump. It may be made operative simply by connecting a tuned circuit H between anode and cathode, and supplying the anode with a positive potential from anode source !2 through radio-frequency choke coil M. The cathode and the negative end of source I2 may be grounded. The tube will then become a self-oscillator and will oscillate in two different modes, depending, to some extent, on the relative diameters of the anode and cathode.

For example, the anode may be made relatively small, as, for example approximately one-half the diameter of the cathode, and when axially positioned with the anode potential adjusted so that the time of flight of an electron from one point on the cathode through the anode to an opposite point is equal to the period of the tuned circuit H, the tube will oscillate on what I term the time of flight principle, and one secondarygenerating impact will occur per cycle. However,

if the anode is increased in diameter and its pe- I riphery placed closely adjacent the inner surface of the cathode, and the anode potential increased, then the electrons will be accelerated outwardly through the apertures in the anode and will then immediately be returned to the cathode at a point adjacent the point from which they were emitted, several times per cycle. Thus, in the latter case. the electrons are accelerated into the Faraday space produced by the anode and returned to the same side of the cathode, rather than completely crossing the operating space. This mode of operation I term the multiple impact per cycle principle. This latter mode of operation does, of course, produce a higher multiplied current, and for that reason I prefer to utilize it. In either case, however, it will be seen that the anode, when energized, forms a Faraday space in the path of the electrons between impacts, and it will also be seen that the anode is positioned within the cathode so that the electrons are accelerated away from the cathode along perpendiculars erected from the cathode surface. These conditions I find desirable, and they distinguish my present tube from prior diodes not capable of producing oscillations, irrespective of outside connections.

Figures 3, 5 and 6 illustrate, diagrammatically, modifications of the fundamental structure shown in Figures 1 and 2. For example, in Figure 3 each end of the cathode B is provided with an inwardly turned flange or bevel l5, thus greatly reducing the open space at the end of the cathode. Inasmuch as my device does not depend in any way upon light for its fundamental operation, such closure of the ends is unimportant from the point of light exclusion, but it does prevent, to a large extent, the escape of electrons from the operating space on to the walls of the envelope. For example, referring to Figure 1, it will be seen by those skilled in the art that the lines of force of thestatic field at the ends of the cylinder will tend to allow electrons to escape-over the edge of the cathode 6 and impact the envelope wall. Inasmuch as these electrons are moving at a relatively high velocity, heating of the walls may occur adjacent the ends of the cathode to such an extent that, in extremely high-power tubes, puncture of the envelope wall may easily take place, or heat strains may be set up, eventually leading to envelope by means of insulating shields l6 and ii, as

shown in Figure 4. 'Here the shields are mounted on one or other of the electrodes, or both, and serve to position the electrodes, and they form a barrier for the passage of electrons. Inasmuch as any electrons impacting these shields will, in all probability, stick and build up a charge on the inward face of the shields, it is obvious that such a charge will, in itself, tendto divert other electrons away from the shields, thus preventing excessive heating thereof.

Figure 5 shows a modification wherein the cathode is in the form of a sphere, and the anode in the form of an inner apertured sphere concentrically positioned with respect to the cathode. The operation will be the same and, of cou'rse,very few electrons can escape from such a structure.

Figure 6 shows a preferred design for a highpower transmitting diode, whereina major portion of the envelopeis a metal cathode 6, in this case being preferably formed of copper, sealed to envelope l with the well known copper-to-glass ring seal l8. The inner surface of the copper cathode 6 may be sensitized as described in conjunction with the cathode of Figure 1, and the cathode may be cooled during operation, if desired. There are. definite advantages in highpower tubes to be obtained by cooling the cathode, inasmuch as the most efficient secondary emitters are usually materials having a low melting point. Thus an excessive rise in temperature of the cathode might, as can readily be seen, damage the emitting surface.

I claim:

1. An electron discharge device comprising an envelope containing as sole electrodes cooperat-I ing to form an electron multiplier and self-oscillator when energized, an unheated hollow cathode defining and substantially enclosing an operating space, the inner surface of said cathode being capable of emitting secondary electrons at a ratio greater than unity upon electron impact therewith, and a hollow anode permeable to electrons positioned within said space and enclosing a portion thereof common to substantially all perpendiculars erected from the adjacent cathode surface.

2. An electron discharge device comprising an i an equipotential space positioned to be traversed byelectrons following substantially all perpendiculars erectedfrom said inner surface.

3. An electron discharge device comprising an envelope containingassole electrodes cooperating to form an electron multiplier'and self-oscillator when energized, an outer unheated cylinder having an inner surface capable of emitting secondary electronsat a ratio greater than unity upon electron impacttherewith, and an inner cylinder permeable to the majority of secondary electrons generated, and shielding means of insulating material closing the open ends of said outer cylinder, said cylinders being concentric.

4; An electron discharge device comprising an envelope containing as sole electrodes cooperating to form an electron multiplier and self-oscillator when energized, an outer unheated cylinder having an inner surface capable of emitting secondary electrons at'a'ratio greater than unity upon electron impact therewith, and an inner cylinder permeable to the majority of secondary electrons generated, the ends of said outer cylinder being directed inwardly to intercept electrons leaving the space enclosed by said outer cylinder, said cylinders. being concentric.

' 5. An electron dischargedevice comprising an envelope containing as sole electrodes cooperating to form an electron multiplier and self-oscillator when energized, an unheated cathode defining and substantially enclosing an operating space, the inner surface of said cathode being capable of emitting secondary electrons at a rato greater than unity upon electron impact therewith, and an apertured Faraday cylinder positioned Within said space: i i

6. An electron discharge device comprising an envelope containing as sole electrodes cooperating to form an electron multiplier and selfoscillator when energized, an unheated cathode defining and substantially enclosing an operating space, the inner surface of said cathode being greater than unity upon electron impact therewith, and an apertured Faraday cylinder positioned within said space, the walls of said cylinder being at all points substantially equidistant from adjacent points on said cathode.

. capable, of emitting secondary electrons at a ratio 7. An electron discharge device comprising an I envelope containingas sole electrodes cooperating to form an electron multiplier and self-oscillator when energized, .an. unheated cathode defining and substantially enclosing an operatingv space, the inner surface of said cathode being capable of emitting secondary electrons at a ratio greater than unity upon electron impact therewith, and electrode means for producing, when energized, a Faraday space permeable to the secondary electrons emitted from said surface.

8. An electron discharge device comprising an envelope containing as sole electrodes cooperating toform an electron multiplier and self-oscillator when energized, an unheated cathode defining and substantially enclosing an operating space, the inner surface of'said cathode being capable of emitting secondary electrons at a ratio greater than unity upon electron impact therewith, and electrode means for producing, when energized, a Faraday space permeable to the secondary electrons emitted along paths perpendicular to said surface.

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