US2237878A - Electron discharge device - Google Patents

Description

April 1941. v. HAEFF ELECTRON DISCHARGE DEVICE' s Sheets-Sheet 1 Filed Feb. 2, 1939 INVENTOR.

ANDREW v. HAEFF BY 4 W ATTORNEY.

s, 1941. A. v. HAEFF 2.237.878

ELECTRON DISCHARGE DEVICE Filed FelS. 2, 1939 s Sheets-Sheet 2 ATTORNEY.

April 1941- A. v. HAEFF 2.237.878

- ELECTRON DISCHARGE DEVICE Filed Feb. 2, 1959 s Sheet-Sheat a I INVEN TOR. ANDRE W M HAEFF ATTORNEY.

Patented Apr. 8, 1941 amaze ELECTRON DISCHARGE DEVICE Andrew V. Haeff, East Orange, N. 3., assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation oi Delaware Application February 2, 1939, Serial No. 254,239

v tion, and a hollow outer tubular'conductor 2! con- 18 Claims.

My invention relates to electron discharge devices, particularly to such devices suitable for use at high frequencies.

It is well known that conventional tubes become inoperative at very high frequencies. The principal difiiculties which prevent operation at high frequencies are due chiefly to the following factorsgthat is, the finite electron transit time producing abnormal loading of the input circuit andloss of trans-conductance of the tube, difiiculty in obtaining necessary small coupling between the output electrode and the input electrode which results in regeneration or excessive loading of the output circuit due to the reflected input losses and the consequent loss of power output and efficiency, and increased losses in the circuit due to the presence of large circulating currents at high frequencies and due to an increase in efiective resistance of the circuit.

The principal object of my invention is to provide an improved electron discharge device particularly suitable for use athigh frequencies.

More particularly it is an object of my invention to provide an electron discharge device in which electron transit time is not critically related to the period of oscillation, which will function satisfactorily at frequencies at which conventional tubes fail to operate, and in which -The novel features which I believe to be char- I tudinal sections of electron discharge devices.

made according to my invention, the associated voltage sources being shown in Figures 6 and '7.

A better understanding of my invention can be had by discussing the principle involved. To illustrate the principle involved in electron discharge devices made according to my invention reference is had to Figures 1 to 4 inclusive. In Figure 1 is schematically shown the longitudinal schematic section of a quarter wave concentric line tank circuit comprising an inner tubular conductor 20 which may be cylindrical in cross seccentric with the inner conductor 20 and electrically connected to the inner conductor 29 by the conducting plate 22. A second tubular conductor 24 which may be referred to as the aperture extension is coaxial with the conductor 2d and spaced axially from the conductor 20 to provide a gap 25. .This tubular conductor 24 and the outer conductor 2| are connected by the conducting plate 23. This arrangement provides a quarter wave concentric tank circuit. If a negatively charged body 26 is projected axially through the inner conductor 20 from left to right, the conditions of the charge distribution on the circuit as the body 25 is moved along the interior of conductors 2B and 25 is indicated in Figures 1 to 4 inclusive. As shown in the figures, there is a positive charge, equal to the negative charge, m. duced on the inside of the inner conductor 'near the body. However, initially no charge appears on the outer surface of the inner conductor 2d. The induced charge moves with the charged body along the inner surface of conductor 20 until the end of the inner conductor 28 is reached. During the passage of the charged body across the gap 25, the charge is partially imaged on the end of the inner conductor 20 and partially on the outer conductor 24 as shown in Figure 2. The passage of the-charged body beyond the gap 25 into the conductor 24 causes the induced charge all to appear on the inner surface of the conductor 25 as shown in Figure 3. The induced charge in transferring from the end of the inner conductor to the conductor 2d flows back over the outer surface of the inner conductor 20 and the inner surface of conductor 2!, thus constituting .a current flow in the quarter wave tank circuit. Ii charged bodies are projected past the gap in proper phase and frequency relationship with respect to the resonant frequency of the tank circuit, the circuit may be made to oscillate vigorously merely by the passage of the charged bodies past the gap.

' Figure 4 illustrates the configuration of the "electric and magnetic fields within the resonant space of the tank circuit when the latter is excited.

' The solid lines 21 represent the electric field distribution and the circles 28 represent the magnetic lines of force; 'The dashed lines 29 represent the equi-potential surfaces in the gap. Along the major part of the length of the tank circuit the direction of the electric field is substantially radial. However, at the gap 25 the electric field has an axial component. The electric field does not penetrate very far inside the open end of the inner conducting member 20 or inside the conductor 24, but is confined effectively to the space defined approximately by the limiting equipotential lines 25 shown in the figures. The space inside the inner conductor 20 and inside the conductor 24 is essentially field free, therefore no work will be done on a charge moving inside the inner conductor 20 by the electric field until the charge reaches the gap 25. If the charge traverses the gap at the instant when the electric force is in the direction from 2| to 24, the charge will be decelerated, its energy being given up to the tank circuit. A charge crossing the gap during the opposite half cycle when the field is reversed will be accelerated and absorb energy from the circuit. If,' however, the number of charges traversing the gap duringthe first half cycle is greater than during the second, the net effect.

will be that energy is supplied to the tank circuit.

Thus, the tank circuit may be excited by passing groups of electrons at the proper frequency across the gap between the conductors 25 and 24. The motion of the electrons in the interior of the inner conductor has no effect on the current in the tank circuit. Also high frequency electromagnetic fields which will be generated within the resonating space of the tank circuit penetrate. but a short distance inside the conductor 20 and conductor 24 which act as a screen electrode so that the electrons will be influenced by these fields only during their the gap.

In Figure 5 is shown schematically in section passage 8,01'055 I an electrode arrangement of a tube embodying rid II, which supply the pulses of electrons in the proper phase relation necessary to excite the tank circuit.- A collector electrode 22 may be placed beyond the screening electrode or aperture extension 24'. If now a high potential is applied between the cathode and the tank circuit including the electrodes 20 and 24' and also between the collector I2 and cathode 10, a stream of electrons from. the cathode will flow toward the collector. If a high frequency voltage is applied between the control grid and the cathode the electron stream will be periodically modulated in intensity. Pulses of electrons traversing the gap 25 will induce high frequency currents between the electrodes 20 and 24'. if the'excitation frequency is adjusted to the resonant frequency of the tank circuit a high imby the tank circuit into the energy of the electromagnetic field within the resonating space between the inner and outer conductors and then may be conveyed to the useful load by means of a coupling loop such as, for example, 33 extending-through an aperture in the outer tubular conductor 2| of the tank circuit.

The high frequency electromagnetic field exgap 25 the coupling between the input electrodes II and 3| and the output electrodes 20 and 24' can be reduced to a negligible value. The collector electrode is also placed at an adequate distance from the gap to minimize coupling between it and the tank-circuit. This results in a reduction of the losses caused by the absorption of radio frequency energy from the tank circuit by the collector.

To minimize the transit time effects the electrodes 20 and-24' can be operated at suitable high potentials with v respect to the cathode. The adjustment of these potentials is not critical because the functioning of the tube does not depend critically upon the electron transit time. This is because the electrons are effective in exciting the output circuit only during the short period of time that they pass through the field extending through the gap-'25. The current collecting electrode 32 can be operated at a much lower potential than the conductors 20 and 24 and in order to obtain a high eillclency it is usually operated at a potentialjust sufficient to collect all decelerated electrons." To improve the functioning of the device an electrostatic or magnetic focusing of the electron stream can be utilized to prevent electrons from impinging on the high potential electrodes 20 or 24. Thus these electrodes will not dissipate energy and all of the power generated in the tube will be supplied by the low voltage collector power supply.

In Figure 6 is shown a tube in longitudinal section and made according to my invention. The main body of the tube, which constitutes a quarter wave concentric line output tank circuit includes a pair of tubular coaxial members or electrodes 35 and 35 separated axially by a gap 31 and electrically connected to a concentric outer cylinder or tubularmember 38 by means of end plates 39 and 40. Mounted within the tubular member 35 is an indirectly heated cathode 4|, the heater of which is not shown, and a grid 42. These electrodes may be disc or rectangular shaped. Electrons supplied by the cathode 4| are projected axially within the cylinders 35 and 35 to a collecting electrode 43 preferably of carbon. -The glass cup members 44 and 45 close the ends of the tubular members 35 and 36 to provide with the member 28 an envelope for the electrodes, the cup-shaped member 44 belng sealed to the tubular member 35 and the cup-shaped member 45 being sealed to the electrode 56 which will be referred to as a screening electrode. The solenoid 45 may be provided for focusing the electrons from the cathode 4| into a well defined beam along the axis of the tubular electrodes 35 and 55. The electrodes 4| and 42 are suitably supported by means of the conductors 41 and 48. A parallel wire transmission line is attached to these conductors. This line forms the input circuit which is tuned by the bridging member 49 provided with the by-passing condenser 50. A loop 5| serves to couple the input circuit to a driver. To permit the tank circuit to be coupled to a load, a reentrant glass portion 53 is extended through an aperture in the outer tubular member 38 to permit the insertion of a. coupling loop 52. The source ofvoltage 54 connected between isting in the resonant space of the tank circuit netrates only a short distance inside the tubur electrode 20 and inside the tubular screen electrode 24. Therefore, by positioning the control electrode 3| at a suitable distance from the the grid and cathode provides a proper bias on grid 42, voltage source 55 being provided for applying to the tank circuit by means of conductor 56' a voltage higher than that applied to the collecting electrode by the power supply 55.

When a high potential Eac at 55 is applied between the cathode and the electrodes 35 and 36 and a voltage'Ecou at 56 between the cathode and collector 43 a stream of electrons from the cathode 4| focused by the magnetic field of the solenoid 46 is projected toward the collector 43 withfrequency of the output circuit 35, .38 and 36, a

high impedance will exist across the gap 31 at this frequency. Consequently, currents induced in electrodes 35 and 36 by electron pulses will produce a high radio frequency voltage across the gap 31. The phase of this voltage at or near resonance will be such as to decelerate electrons passing during the half period of maximum intensity of electron current in the stream. The energy of the decelerated -electrons is converted by the tank circuit into energy of the electric and magnetic fields in the resonant space between the inner 35 and outer-38 cylinders and then transferred to the useful load by the coupling loop 52.

The radio frequency fields penetrate only a short distance inside the tubular electrode 35 and inside the screening electrode 38, a distance effectively less than their diameter so that by positionin the cathode 4!, control electrode 42 and the collector .43 at suitable distances from the gap 31, the coupling between the output tank circuit and these last three mentioned electrodes can be made practically negligible. To reduce electron transit time between the control grid 42 and the gap, the electrodes 35 and 36 can be operated at suitably high potentials to increase the speed of the electrons past the gap. However, to obtain high efficiency, the collector electrode potential can be adjusted to a value just sufllcient to collect all decelerated electrons and usually has to be only slightly higher than the effective peak radio frequency voltage existing across the gap. The adjustment of the accelerating potential Eat: is not at all critical. It is usually adjusted to such a value that the transit time of electrons across the effective length of the gap (smaller than the diameter of the electrode 35) is a fraction of a period so that the loss in transconductance due to transit time is small. With proper design and a sufficient focusing field there is no current to electrodes 35 and 36, so that these electrodes dissipate no energy. The power is supplied only by the collector power supply 56.

In Figure 7 is shown an arrangement in which the output electrodes and tank circuit are external to the tube envelope. In this case the inner tubular member or electrode 60 and screening eelctrode Bl are joined and electrically connected to the outer tubular member 62 by means of conducting plates 53 and 56. These-elements form the concentric line output tank circuit. The resonant frequency of the tank circuit may be varied by means of the adjustable condenser plate 16 movable by insulated rod 16 toward and from the electrodes Gil and SI to increase or decrease the capacity coupling between these two electrodes. The edges of the electrodes 60 and iii are thickened and rounded as at 60 and 6| to prevent excessive radio frequency fields at ,ferred from the tank circuit by the gap with a consequent dielectric loss in the glass envelope 66 housing the cathode and collector electrodes. To minimize these losses the glass envelope may be provided with a short section near the gap made of low loss dielectric such as special glass, quartz or ceramic. To provide cooling for the tube and'particularly to effect adequate cooling of the glass envelope in the region of maximum electric field at the gap 9. special cooling arrangement can be provided as shown by providing a reentrant portion contacting the glass envelope and forming with the inner tubular members 60 and GI a hollow tubular casing around the envelope into which air can be forced through tubes 65 and 65", as indicated. The whole external concentric line tank circuit-and the glass envelope can be separated at will. Envelope 66 which fits within the concentrictank circuit is provided with an indirectly heated cathode 6! (heater not shown). control grid 68 and focusing electrode 69,, which can be maintained at either control grid potential or any suitable potential serving -to concentrate the electron stream at the start and making it possible to use considerably weaker magnetic foucusing fields from solenoids M and 15 without undesirable current absorption-by-the acceelrating electrodes I0 and H positioned between the cathode and collector electrode 12 supported from the press 13. The reason for using the accelerating electrodes 10 and- II is to avoid the undesirable effects of charges on the glass wall due to bombardment by stray electrons. at a suitable distance from. the gap between the electrodes 60 and BI of the output tank circuit so that the radio frequency fields from the space between the tubular members 60 and 62 do not reach them, and thus electrodes 70 and H do not form a part of the output circuit and do not carry circulating currents. The electron stream from the cathode 61 modulated by grid 68 focused by the electrode 69 traverses the gap between electrodes 60 and BI. As in the previous case a high radio frequency voltage will be de' veloped across the gap and electrons will be decelerated in the gap and finally after passing accelerating electrode H will be collected by means of electrode 12. Radio frequency energy is transthe coupling loop 62' to the load.

A parallel wire transmission line comprising tubular conductors 19 and tuned by a conducting bridge 8| form the input circuit. Conductors 69' and 11 connected to the focusing electrode 69 and grid 68 extend through tubular member 79 and are connected to, the voltage sources 59" and 68' to provide the biasing volt- 68. The tubular member 80 and the insulated conductor I8 within the tubular member furnish the cathode heating current from the source of voltage supply 61' and the conductor 80 at the same time acts as the cathode lead. Adequate by-passing for high frequency currents is provided by the condenser 80'. preferably placed ins de the glass envelope and connected between the heater and cathode leads. Radio frequency coupling between the transmission line conductor 19 and 80 and the grid and the focusing electrodes is due to the inherent capacity-between these conductors and the insulated leads within the hollow conductor tubes. If necessary, additional condensers for capacity The electrodes=""l0 and H are positioned ages for the focusing electrode 69 and the grid coupling can be provided between the conductor tubes and the leads. I

One sample of a tube made according to my invention has an external member 82 of a length .of 6" and diameter of 2", the inner tubular the edge ofthe accelerating electrode II. The

collecting electrode 12 has an outside diameter of 2" and a depth of 2". It is of course understood that these dimensions could be changed or varied for different frequencies and for different power outputs.

The tube was operated under the following conditions: At a frequency of 450 megacycles, power output of 110 watts was obtained, the driving power being about watts and the emciency about 35%. The accelerating voltage applied to electrode is and II was of the order of 6000 volts and the collector electrode voltage of the order of 2000 volts. The collector current. was approximately 150 milliamperes. The.

extremely low loss in the accelerating electrodes 10 and ll is shown by the fact that less than .1

milliamperes was the current to these electrodes.'

This performance which is readily'obtained with r a tube made according to my invention contrasts sharply with tubes and circuits of conventional design when an attempt is made to operate them at the higher frequencies.

A modified form of my invention is shown in longitudinal section in Figure 8. Here the cathode 4i and grid 42' are outside of the tubular conductor and the collector 0' inside the tubular electrode 36'. The glass cup members 44' and 45' seal the ends of the-tubular members which with the outer tubular member 3| are electrically connected by plates 39' and 40' thus forming the tube envelope. The solenoids 46' and I1 furnish a magnetic field and coupling to an output circuit is obtained by means of loop 52' suitably sealed in plate ll by means of the glass cup-shaped member ll.

A further modification showing a symmetrical type of circuit is shown in longitudinal section in Figure 9. The tubular electrode members II and 80 are electrically connected to the conducting discs or plates 88 and IQ, which with the cylindrical short'circuiting member 00 form the tank circuit. The member 01 is sealed to gap between the two electrodes. The diameter; of the space defined by the circular disc shaped conductors l8 .and 8! and the, cylindrical short circuiting member I! determine the resonant frequency of the output circuit. A. condenser of the type shown in Figure 7 could be used to vary the resonant frequency. Because the tank circuit members SI, 30 and II are outside the tube envelope proper, they can be -changed'to provide a tank circuit having a different, resonant frequency.

In Figure 10 is shown a modification of the symmetrical type shown in Figure 9 in'which a coupling condenser plate so is supported by bel-- lows seal 81. The coupling can be adjusted by means of screw member 98. Collector electrode 43" is hollow to provide for water cooling as indicated. Cup shaped members ll, ll" and IS,- the last sealed to the extension 94, provide the necessary insulating supports for the various electrodes and coupling loop.

Figure 11 diflers from Figures 9 and 10 in that the tubular electrodes 85' and 86' along with the remainder of the tank circuit and tuning condenser 96 are mounted on the exterior of the glass envelope 60', at one end of which is mounted a cathode ll and grid 41', and in the other end collector electrodes If; accelerating electrode 60' and 13' being provided between the cathode ll and collector Is". This construction permits separation of the envelope and tank circuit at will.

Thus in a tube made according to my inven tion electron transit time effects are minimized by utilizing electrons of high velocity. This is accomplished without increasing dissipation and loss in eillciency by separating the'functions of the output electrode and current collecting electrode and by making use of electron focusing. The output-input coupling is reduced to a negligible value by screening and separation of the electrodes and. circuits. The high frequency losses due to high frequency voltages are minimized by current; carrying electrodes of large ments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in'the appended claims.

What I claim as new is:

1. An electron discharge device having a tank circuitincluding a pair of concentric tubular members and another tubular member coaxial 'with and spaced axially from the inner of the circuit includingan inner tubular member and 4 a concentric outer tubular member. said members being-spaced from each other and connected at one end by a conducting member, a third tubular member coaxial with the inner tubular member and spaced from the inner tubular member to provide a gap, a conducting member connecting the other end of the outer tubular member to said third tubular member, means for projecting a stream of electrons axially of said inner tubular member across said gap, means for modulating said stream of electrons prior to the passage of the stream across said gap, and means for collecting the electrons in said stream after passage of the electrons across the gap.

3. An electron discharge device having a cathode for supplying electrons, a collector electrode spaced from said cathode for receiving said electrons, means including an oscillating tank circuit having a pair of coaxial tubular members spaced axially to provide a gap between said coaxial tubular members and a concentric outer tubular member surrounding said coaxial tubular members and electrically connected'at each end to a different one of said tubular members, said tubular members being positioned between the cathode and collector electrode whereby electrons moving from the cathode to the collector electrode will pass axially through the tubular members across said gap.

4. An electron discharge device having a cathode for supplying electrons and a collector electrode spaced from said cathode for receiving said electrons, an oscillating tank circuit including a pair of coaxial tubular electrodes spaced axially to provide a gap between said tubular electrodes provide an envelope for said cathode and collectr ing electrodes.

5. An electron discharge device including a quarter wave-concentric line output tankcircuithaving a pair of coaxial tubular members spaced axially to form a gap and a concentric outer tubular member conductively secured at each end to one of said coaxial tubular members, a cathode and grid' positioned adjacent one end of one of -said pair of coaxial tubular members for supplying electrons axially of said coaxial tubular members across said gap and a collecting electrode adjacent an end of the other coaxial tubular member for receiving the electrons from the cathode. r

6. An, electron discharge device including a quarter wave concentric line output tank circuit having a pair of coaxial tubular members spaced axially to form a gap, and a concentric outer tubular member conductively secured at each end to one of said coaxial tubular members, a cathode and grid positioned adjacent one end of one of said pair of coaxial tubular members for supplying electrons axially of said coaxial tubular members across said gap and a collectingelectrode adjacent an end of the other coaxial tubular member for receiving the electrons from the cathode, and insulation means closing the opposite ends of the coaxial tubular members to form an envelope for said cathode, grid and collecting electrode.

'7. An electron discharge device including a quarter wave concentric line output tank circuit having a pair of coaxial tubular members spaced axially to form a gap and a concentric outer tubular member electrically connected at each end to one of said coaxial tubular members, a cathode and grid positioned adjacent one end of one'of said pair of coaxial tubular members for supplying electrons axially of said coaxial tubular members across said gap and a collecting electrode adjacent an end of the other of said pair of coaxial tubular members for receiving theel'ectrons from the cathode, and insulation means closing the opposite ends of the pair of coaxial tubular'members to form an envelope for said cathode, grid and collecting electrode, and means including an electromagnetic coil for focusing the electrons projected through said coaxialtubular membersfrom said cathode to said collectin electrode into a well defined beam.

8. An electron discharge device including a quarter wave concentric line output tank circuit having a' pair of coaxial tubular members spaced axially to form a gap and a concentric outer tubular member electrically connected at each end to one. of said coaxial tubular members, a

cathode and grid positioned in one of said pair of coaxial tubular members for supplying electrons axially of said coaxial tubular members across said gap and a collecting electrode adjacent an end of the other coaxial tubular member for receiving the electrons from the cathode, insulation means closing the opposite ends of the pair of coaxial tubular members to form an envelope for said cathode, .grid and collecting electrode, means including an electromagnetic coil for focusing the electrons projected through said coaxial members from said cathode to said collecting electrode into a well defined beam, and a loop conductor extending through the outer tubular member for inductively coupling the concentric line tank circuit to an output circuit.'

9. An electron discharge device including a quarter wave concentric line output tank circuit having a pair of coaxial tubular members spaced axially to form a gap and a concentric outer tubular member connected bya conducting plate at each end to one of said coaxial tubular members, a cathode and grid positioned in one of said pair of coaxial tubular members for supplying electrons axially of said coaxial tubular members across said gap and a collecting electrode adjacent an end of the other coaxial tubular member for receiving the electrons from the cathode, and

insulation means closing the opposite ends of the coaxial tubular members to form an envelope for said cathode, grid and collecting electrode, means including anelectromagnetic coil for focusing the electrons projected through said coaxial members from said cathode to said collecting electrode into a well defined beam, a loop conductor extending through the outer tubular member for inductively coupling the concentric line tank circuit to an output circuit, and a transmission line having one end connected to the grid and the other end connected to said cathode for coupling said electron discharge device to a driving circuit.

10. An electron discharge device including a cathode and grid for supplying a modulated stream of electrons and a collecting electrode for receiving said modulated stream of electrons, and a quarter wave concentric line output tank circuit having a pair of coaxial tubular members spaced axially to provide a gap and surrounding the-discharge path between the cathode and anode whereby electrons from the cathode to the anode traverse the gap between said tubular members, and means including a conductor extending across the gap between said coaxial members but spaced from said coaxial members and movable transversely with respect to said costream of electrons and anelectrode for collecting electrons in said stream, a pair of coaxial tubular members spaced axially to form a gap therebetween surrounding the discharge path be- 7 tween the cathode and the collecting electrode, a conducting plate member secured to each of said coaxial tubular members intermediate the ends of the tubular members and electrically connected at theirperipheries by a conducting cylindrical member to form with said tubular members a closed compartment.

12. An electron discharge device including'a cathode and grid for supplying a modulated stream of electrons and an electrode for collecting electrons in said stream, a pair of coaxial tubular members spaced axially to form a gap therebetween surrounding the discharge path between the cathode and the collecting electrode, a conducting plate member secured to each of said coaxial tubular members intermediate the ends of the tubular members and electrically connected at their peripheries by a conducting cylindrical member and electromagnetic means surrounding each of said tubular members for focusing the electrons from the cathode to the collecting electrode into a well defined beam.

13. An electron discharge device including a cathode and grid for supplying a modulated stream of electrons and an electrode for collecting electrons in said stream, a pair of coaxial tubular members spaced axially to form a gap therebetween surrounding the discharge path between the cathode and the collecting electrode, a conducting plate member secured to each of said coaxial tubular members intermediate the ends of the tubular members and electrically connected at their peripheries by a conducting cylindrical member, and a solenoid surrounding each of said tubular members spaced axially to form a gap therebetween surrounding the discharge Path between the cathode and the collecting electrode, a conducting plate member secured to each of said coaxial tubular members intermediate the ends of the tubular members and electrically connected at their peripheries by a conducting cylindrical member to form a tank circuit and a conductor bridging the gap and overlapping but out of contact with the adjacent ends of the coaxial members and movable transversely to the coaxial members to change the capacity coupling between said members to vary the frequency at which the tank circuit will oscillate, and a conducting loop extending through an aperture in said conducting cylindrical member to couple the tank circuit to a load.

15. An electron discharge device having a tank circuit comprising a unitary hollow body with a passageway extending through said hollow body and having a gap within said passageway extending entirely around said passageway in a plane transverse to said passageway, a cathode for supplying electrons axially of said passageway past said gap, a grid for modulating said electrons prior to said passage past said gap, and means forfcollecting the electrons after the passage of electrons past said gap.

16. An electron discharge device including a quarter-wave concentric line output tank circuit having a pair of coaxial tubular members spaced axially and forming a gap, and a concentric outer tubular member connected by conducting plates at each end to one of said coaxial tubular memthe outer tubular member for inductively ,cou-- pling the tank circuit to an output circuit and a transmission line having one end connected to a grid and the other end connected to said cathode for coupling said electron discharge device to a driving circuit.

17.'An electron discharge device including a cathode and grid for supplying a modulated stream of electrons, and an electrode for collecting electrons in said stream, a pair of coaxial tubular members spaced axially and forming a gap therebetween surrounding the discharge path between the cathode and collecting electrode, a conducting plate member secured to each of said coaxial tubular members intermediate the ends of the tubular members and a conducting mem ber electrically connecting said plates at their peripheries, and electromagnetic means surrounding said tubular members for focusing the electrons projected from the cathode to the collecting electrode in a well defined beam.

- 18. An electron discharge device having a tank a circuit comprising a hollow body formed by the surface of revolution of a geometric figure and having a resonant frequency and having a passageway extending through said hollow body,

said passageway having a gap extending entirely" around said passageway in a plane transverse to said passageway, a cathode for supplying electrons axially of said passageway past said gap, 11

grid for modulating said electrons prior :to said passage past said gap, and means for collecting the electrons after the passage of electrons past said gap.

ANDREW V. HAEFF.

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