US2293387A - Electron discharge device - Google Patents

Description

Aug. H8, w42. A. y. HAEFF 2,293,387

ELECTRON DISCHARGE DEVICE Original Filed Feb. 2, 1959 2 Sheets-Sheet 1 A T TORNEY.

Aug ES H942 A. v. HAEFF ELECTRON DISCHARGE DEVICE original Filed Feb. 2, 1939 2 Sheets-Sheet 2 :g l IEIHHIBIH INVENTOR. ANDREW if. HAEFF A TTORNE Y.

Patente-d ug. i8, 1942 UNM@ STATES PATENT OFFICE ELECTRON DISCHARGE DEVICE Andrew V. Haefi, East Grange, N'. lf., assigner to Radio Corporation of America, a corporation of Delaware 1s claim. (cl. 25o-27.5)

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

The present application is a division of my application which issued as United States Patent 2,237,878 on April 8, 1941.

It is well known that conventional tubes become inoperative at very high frequencies. The principal dimculties which prevent operation at high frequencies are due chiefly to the following factors, that is, the finite electron transit time producing abnormal loading of the input circuit and loss of transconductance of the tube, difficulty 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 emciency, and increased losses in the circuit due to the presence of large circulating currents at high frequencies and due to an increase in eective resistance of the circuit.

The principal object of my invention is to provide an improved electron discharge device particularly suitable for use at high 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 high frequency losses are minimized.

A further object of my invention is to 'provide an electron discharge device particularly suitable for use as an amplifier at very high frequencies.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawings in which Figures 1 to 4 inclusive are schematic diagrams i1- lustrating the principles of my invention, Figure 5 is a simplified diagrammatic representation of an electron discharge device made according to my invention, and Figures 6 to 11 inclusive are longitudinal 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. 1n

Figure 1 is schematically shown the longitudinal 55 schematic section of a quarter wave concentric line tank circuit comprising an inner tubular conductor 20 which may be cylindrical in cross section, and a hollow outer tubular conductor 2| concentric with the inner conductor 20 and electrically connected to the inner conductor 20 by the conducting plate 22. A second tubular conductor 2t which may be referred to as the aperture extension is coaxial with the conductor 29 and spaced axially from the conductor 20 to provide a gap 25. This tubular conductor g4 and the outer conductor 2l 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 ythrough the inner conductor 28 from left to right, the conditions of the charge distribution on the circuit as the body 26 is moved along the interior of conductors 20 and 2d is indicated in' Figures 1 to inclusive. As shown in the gures, there is a positive charge, equal to the nega-` tive charge induced on the inside of the inner conductornear the body. However, initially no charge appears on the outer surface of the inner conductor 20. The induced charge moves with the charged body along the inner surface of conductor 2@ until the end of the inner conductor 29 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 2B and partially on the outer conductor 2B as shown in Figure 2. The passage of the charged body beyond the gap 25 into the conductor 2B causes the induced charge all to appear on the inner surface of the conductor 2t as shown in Figure 3. The induced charge in transferring from the end of the inner conductor to the conductor 26 flows back over the outer surface of the inner conductor 29 and the inner surface of conductor 2i, thus constituting a current iiow in the quarter wave tank circuit. 1f 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 conguration 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 eld distribution and the circles 28 represent the magnetic lines of force. The dashed lines 2! represent the equi-potential surfaces in the gap. Along the major part of the length of the tank circuit the direction of the electric eld is sublstantially radial. However, at the gap 25 the electric eld has an axial component. The electric eld does not penetrate very far inside the open end of the inner-conducting member 20 or inside the conductor 24, but is conilned eiectively to the space dened approximately by the limiting equipotential lines 29 shown in the figures. The space inside the inner conductor 20 and inside the conductor 24 is essentially eld 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 20 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 iield is reversed will be accelerated and absorb energy from the circuit. If, however, the nurnber of charges traversing the gap during the rst 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 2li and 24. The motion of the electrons in the interior ofv the inner conductor 20 has no effect on the current in the tank circuit. Also high frequency electromagnetic'ilelds which will be generated within the resonating space of the tank circuit penetrate but a short distance inside the conductor 2t and conductor 24 which act as a screen electrode so that the electrons will be inuenced circuit including electrodes 20 and 24' and also Y between the collector 32 and cathode 30. 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 freouencv currents between the electrodes 20 and v24'. If the excitation frequency is adjusted to the resonant freouency of the tank circuit a high impedance will exist across the gap-25 at this frequency. The induced currents, therefore, will produce a high radio frequency voltage across the gan 25. The phase of this voltage at or near resonance lwill be such as to decelerate electrons traversing the gap during the half period of maximum intensity oi' the .electron current in the stream.

'I'he energy lost by the electrons is transformed by the tank circuit into the energy oi' the electromagnetic iield within the resonating space between the inner and outer conductors and then may be conveyed to 'the useful load by means o f a coupling loop such as, for example, 33 extending through an aperture inthe outer tubular conductor El of the tank circuit.

'Ihe high yfrequency electromagnetic ileld existing in the resonant space of the tank circuit penetrates only a short distance insidethe tubular electrode 20 and inside the tubular screen electrode 24. Therefore, by positioning the control electrode 3| at a suitable distance from the gap 25 the coupling between the input electrodes 30 and 3| and the output electrodes 2|! 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 lossesv caused by the absorption of radio frequency energy from the tank circuit by the collector. Y

To minimize the transit time effect the electrodes 20 and 24' can be operated at suitable high potentials with 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. 'Ihis is because the electrons are effective in exciting the output circuit only during the short period of time that they pass through the ileld extending through the gap 25. The current collecting electrode 32 can be operated at amuch lower potentialthan the conductors 20 and 24' and in order to obtain a high efflciencyit is usually operated at a potential just suiflcient 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 36 separated axially by a gap 31 and electrically connected to a concentric outer cylinder or tubular member 38 by means of end plates 39 and 40. Mounted within the tubular member 35 is an indirectely 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 36 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 38 an envelope for the electrodes, the cup-shaped member 44 being sealed to the tubular member 35 and the cup-shaped member 45 being sealed to the electrode 36 which will be referred to as a screening electrode. The solenoid 46 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 36. The lelectrodes 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, an aperture 38' is provided in the outer tubularmember 38, surrounded by an extension or collar 38". A reentrant glass portion 53 sup- 'that these electrodes dissipate no energy.v

assess? ported on and sealed to the extension 38" is extended through the aperture Il' in the outer tubular member it to permit the insertion of a coupling loop lll and to seal the tank circuit.

The source oi' voltage lid connected Ibetween the Y grid and' cathode provides o. proper bias on grid di, voltage source till being providedfor applying to the tanh `circuit by means of conductor tt' a voltage higher than that applied to the collecting electrode by the power supply til.

when a high potential de at B is applied between the cathode and the electrodes lill endl@ and a voltage Emu at llt between the cathode and collector G3 a stream of electrons from the cathode li focused by the magnetic eld of the solenoid 4l@ is projected toward the collector 68 without imninsind on either electrode St or 536. Ii a radio frequency voltage is applied betwn control grid l and cathode di by exciting the input circuit the electron stream will be periodically modulated in intensity. Pulses of electrons traversing the gap fil will induce radio frequency currents' in the electrod 8d and 8f3. lli .the encitation frequency is adjusted to the resonance frequency oi the output circuit 35. 39 andllla high impedance will exist across Athe gap 3l at this frequency. Consequently, currents induced' in electrodes @El ond SG by electron puls@ `evill produce a'high radio'ireqluency voltageecrm the gap 8l. The phase oi'this voltage at or near resonance will be such es to decelerate electrons passing during the half period oi maximum intensity oi electron current in the stream. The energy ci the decelerated electrons is converted by the tank circuit into energy oi the electric and magnetic nelds in the resonant space between the inner 85 and outer 88 cylinders and then transferred to the useful load by the coucling loop B2.

The radio frequency nelds penetrate only a short distance inside the tubular electrode d5 and inside the screening electrode 38. a distance el iectively less than their diameter so that by mn tloning the cathode di; control electrode il and the `collector lil at suitable distances trom the sap 3l, the couplins between the output tank circuit and these last three mentioned electrodes can loe made practically negligible. To reduce electron transit time hetweni the control grid dil and the gap, the electrodes t5 and 8S can he operated et suitable nich potentiele to increase the speed oi the electrons past the gesp. Hop ever, to ohtmn edlilency, the collector electrode potentiel can he adjusted to a value lust snmcient to collect lall decelerated electrons md usually has to he only slightly higher than the edective com radio ireouen'cy voltage vcristinay across the gap. The adjustment o? the accelera ating' potential lds@ is not at all crlticel. lt is usually udine-ted m such a value that the time oi electrons across the edectlve length o? the gap (anali-er than the diameter oi the elec trede Sli) is a Erection oi a period so that the lern in trensconductmce due to transit is With proper and a sumcient locusing ideld is no current 'to electrodes 85 and 853 so The correr is supplied only hy the collector 58.

F? is shown on in n the outp ctrodes and tenir are en tornai to tute envelope. 'ln this the inner tuloular menacer or electrode f5@ and ocres".-

Si are joined and electricelly con were@ lo cuter @il ty o! conducting plates B3 and 54. These elements `form the concentricl line output tank circuit.

The resonant frequency oi the tank circuit may be varied by means of the adjustable condenser plate 'I5 movable by insulated rod 'It' toward and from the electrodes and 8i to increase or de'- crease the capacity coupling between these two electrodes. The edges of the electrodes 60 Vand di are thickened and rounded as at te' and Il' to prevent excessive radio frequency elds at the gap with a consequent dielectric loss in the glass envelope t@ housing the cathode and collector electrodes. Tominimize these losses the glass envelope may be provided with Ha 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-eiiect adequate cooling of Ythe glass envelope in the region of maximum-electric eld at the gap a special cooling arrangement can be provided as shown by providing a reentrant portion t5 contacting the glass envelope and forming with the inner tubular members t@ and 6i a hollow tubular casing around the envelope into which air can be forced through tubes t5' and tt", as indicated. The whole external concentric line tank circuit and the glass envelope can be separated at will. mvelope 556 which tits within the concentric tank circuit is provided with an indirectly heated cathode 6l (heater not shown), control grid ed and focusing electrode til, 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 locusins delds from solenoids ld and lll without undesirable current absorption by the accelerating electrodes 'l0 l and li positioned between the cathcde and collector electrode l2 supported from the press i8. The reason lor using the accelerating electrodes l0 and li is to avoid the undesirable -edects ol charges on the glass wall due to bombardment hy stray electrons. The electrodes l@ end li are positioned at a suitable distance from the gap between the electrodes BQ and @i oi the output tenir circuit so that the radio ire quency delds from the space between the tubular members GU and @l do not reach thorn, and thus electrodes l@ end li do not form a part of the output circuit and do not carry circulating currents. The electron stream from the cathode lll modulated py grid S0 focused by the electrode 69 traverses the sap' between electrodes O@ and ci. is in the previous case a high radio lreduency voltage will ce developed across the gap and electrons will he decelerated in the aap and nnslly alter passing accelerating electrode ll will te collected hy means oi electrode il. Radio irenuency energy is transferred from the tenir circuit hy the coupling loop Gl' to the load.

A persllel wire www., on line comprising tubular conductors lli and El@ tuned by e conduct ing bridge Si iorni the input circuit. Conductors 6d' and El connected to the focusing electrode d@ and grid @il entend through tubular member l@ and are connected to the voltage sources 69" and 58' to provide the hissing voltages lor the locusing electrode Si) and the grid Gd. Thetuloular member 8O md the insulated conductor 'JQ rwithin the tubular member iurnish the cathode heating n current from the source oi voltage supply 6l' and bers l and 8l having a diameter just sufficiently large to permit slipping the concentric line unit over the end of the envelope 66 having an outside diameter of 1%". The gap between the inner tubular member 80 and 8l was of the order of The accelerating electrode 'H with a width of t'fwas spaced 2" from the accelerating electrode Il having a width of 1", the focusing electrode being spaced 115" from the edge of the accelerating electrode 10. The collecting electrode 'I2 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 frequencles and. for different power outputs.

The tube was operated under the following con-.- ditlons: At a frequency of 450 megacycles, power output of 110 watts was obtained, the driving power being about watts and the eillciency about 35%. The accelerating voltage applied to electrode 10 and 1I 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. l'I'he extremely low loss in the accelerating electrodes 10 and 1I is shown by the fact that less than .1 milliampere was the current tol these electrodes. This performance which is readily obtained with 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.

Thus in a tube made according to my invention electron transit time effects are minimized by utilizing electrons of high velocity. This is accomplished without increasing dissipation and loss in eiliciency by separating the functions of the output electrode and current collecting electrode and by making use` of electron focusing. 'I'he output-input coupling is reduced to a negligible value by screening and separation of the Y electrodes and circuits. 'I'he high frequency losses due to high frequency voltages are minimized by current carrying electrodes of large periphery.

` In addition to the above advantages high eilieiency results due to collection of the electrons at low velocity and high power output is attained because the collector may be made Iof adequate size without inuencing the performance of the output circuit. A non-regenerative ampliication is made possible through the reduction of the yrmtput-inlrut coupling to a negligible value.

Other uses to `which my invention may be put are for example frequency multiplication an generation of oscillations.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specic 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 J be made in the particular structure used and the se for which it is employed Without depart-n ing from the scope of my invention as set forth in the appended claims.

What I claim as new is:

1. An electron discharge device including a cathode and grid for supplying a modulated stream of electrons anda 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 axially spaced 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 pair of coaxial tubular members, and accelerating means including a pair of electrodes surrounding the path of the beam between the cathode and the collecting electrode.

2. An electron discharge device including an envelope containing a cathode and grid for sup plying amodulated stream of electrons and an electrode for collecting electrons in said stream, a tank`circuit surrounding said envelope and including a pair of coaxial tubular members spaced axially to form a gap therebetween surrounding the discharge path between the cathode and the collecting electrode, and electromagnetic means surrounding said tubular members for focusing the electrons from the cathode to the collecting electrode into a well-defined beam.

3. An electron discharge device including an` envelope containing a cathode and grid for supplying a modulated stream of electrons and an electrode for collecting electrons in said stream, an accelerating means within said envelope and including a pair of electrodes surrounding the path of the electrons between the cathode and collecting electrode, a tank circuit surrounding said envelope and including a pair of coaxial tubular members spaced axially to form a gap therebetween surrounding the discharge path between the cathode and the collecting electrode, and electromagnetic means surrounding said coaxial tubular members for focusing they electrons from the cathode to the collecting electrode into a well-defined beam, and a conductor bridging the gap and overlapping but out of contact with the adjacent ends of the coaxial tubular members and movable transversely of the coaxial tubular members to change the capacity coupling between said coaxial tubular members.

4. An electron discharge device including an envelope having a cathode and grid for supplying a modulated stream of electrons and an electrode for collecting electrons in said stream, and accelerating means within said envelope and including la pair of electrodes surrounding the path of the stream between the cathode and the co1- lecting electrode, 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 tuburlar members intermediate the ends of the tubullas 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 tubular members electrode for collecting said electrons, a hollow tank circuit surrounding said envelope and having a gap lying in a plane transverse to the stream of electrons and between the grid and collecting electrode, said tank circuit being spaced from said envelope to provide a passageway between the envelope and the tank circuit, and means for directing a cooling medium between theenvelope and the tank circuit.

6. An electron discharge device including an envelope containing a cathode and grid for supplying a modulated stream of electrons, and an electrode for collecting the electrons in said stream, an elongated hollow tank circuit surrounding said envelope and including a pair of coamal tubular members spaced axially to form a gap therebetween surrounding the discharge path between the cathode and the collecting electrode, said tubular members being spaced from said envelope to provide a passageway between the envelope and the tubular members, and means for directing a cooling medium between the envelope and the tubular members into the interior of the tank circuit through said gap, said last means including extensions on opposite ends of said tank circuit and enclosing a space around the envelope, said space communicating with the space between the tank circuit and envelope and having inlets for introducing the cooling medium.

7. An electron discharge device including an envelope containing a cathode and a grid for supplying a modul-ated stream of electrons, and an electrode for collecting the electrons in said stream, a hollow tank circuit surrounding said envelope and including a pair of coaxial tubular members spaced axially to form a gap therebetween surrounding the discharge path between the cathode and collecting electrode and a conacr ducting member surrounding said coaxial tubular Y members and secured and electrically connected to each of said coaxial tubular members, said coaxial tubular members being spaced from the envelope to provide an annular passageway between the envelope and the tubular members, inlet means for directing a cooling medium between the envelope and the inner tubular mem- .bers through said gap into the interior oi said tank circuit, said conducting member surrounding said tubular members being provided with an aperture through which the cooling medium can pass to the exterior of the tank circuit.

8. An electron discharge device including an envelope containing a cathode and grid :for supplying a modulated stream of electrons and an electrode ior collecting the electrons in said stream, accelerating means within the envelope and including a pair of electrodes surrounding the path'oi the electrons between the cathode and. the collecting electrodes,- a twk circuit surrounding said envelope and including a pair oi coaxial tubular members spaced axially toform e, gap theretbetween surrounding the discharge path between the cathode and the collecting electrede and .a conducting member surrounding said coamal tubular member and secured and elec2 tricallr connected to each of said coaxial tubular members, and electromagnetic means surround= the conducting member for io cusing electrons from the cathode to the collecting electrode into a welldeiined beam.

9. hn electron discharge device including an envelope a cathode and grid for supplying a modulated stream of electrons and an electrede for collecting electrons in said stream and accelerating means within said envelope and in=1 iti cludin'g a pair of electrodes surrounding the path of the beam between the cathode and the collecting electrode, a tank circuit surrounding said envelope and including a pair oi coaxial tubular members spaced axially to form a gap therebetween surrounding the discharge path between the cathode and the collecting electrode and 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 conductor bridging the gap and overlapping but out of contact with the adjacent ends of the coaxial tubular members and movable transversely of the coaxial members to change the capacity coupling between said mem- :bers to vary the frequency at which the tank circuit will osoillate, and electromagnetic means surrounding each of the coaxial tubular members. 10. An electron discharge device including a cathode and grid for supplying a. modulated stream of electrons, and a collecting electrode for collecting electrons` in said stream, and a hollow tank circuit surrounding said stream of electrons and including a pair of coaxial tubular members spaced axially to form a gap therebetween'surrounding the discharge path between the cathode and collecting electrode and a conducting plate member secured to each of said coamal tubular members intermediate the ends of the tubular members and a conducting member 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, said conducting member electrically connected to the peripheries oi the conducting plate members having an aperture and a reentrant extension of insulating material extending within said aperture and sealingsaid tank circuit, and a conducting loop extending within the reentrant insulating extension for coupling the electron discharge device to an output circuit.

11.. An electron discharge device having a cathode for Supplying a stream or electrons and means for collecting said electrons, a hollow tank circuit having a passageway extending therethrough through which the electrons iromthe cathode pass to the collecting means, said passageway having a gap surrounding the discharge path between the cathpde and the collecting means, an insulating means closing one end of the passageway to provide with the hollow tank circuit an envelope for the cathode, said hollow tank circuit having an aperture extending through the outer surface thereof, and an insulating closure member supported within said aperL ture and sealing said aperture in said hollow tank circuit, and a conducting coupling member extending within the hollow tank circuit through said aperture.

l2. lin electron discharge device having a cathode ior supplying a stream oi electrons and means ior collecting said electrons, a hollow tank circuit having a j.=assagewav extending therethrough through which the electrons from the cathode paas to the collecting means, said pas= sagewar having a gap surrounding the discharge path between the cathode and the collecting means, an insulating means closing one end or the passageway to provide with the hollow tank circuit an envelope for the cathode, said hollow tank circuit having an aperture extending through the outer surace thereoi and ons tension around said aperture, and an insulating closure member supported by said extension and sealing said aperture in said hollow tank circuit, and a conducting coupling member extending through the extension within the hollow tank circuit.

13. An electron discharge device having a cathode and grid for supplying a modulated stream of electrons and means for collecting said electrons, a hollow tank circuit having a passageway extending therethrough through which the electrons from the cathode pass to the collecting means. said passageway having a gap surrounding the. discharge path between the cathode and the collecting electrode, and insulating means closing one end of the passageway to provide with the hollow tank circuit an envelope for the cathode and grid, said hollow tank circuit having an aperture extending through the outer surface thereof and an extension around said aperture and insulating material supported by said extension and sealing said aperture in said tank circuit and a conducting coupling member extending through the extension within the hollow tank circuit.

14. An electron discharge device having a tank circuit comprising a hollow body formed by a surface of revolution and having a resonant frequency and 4having a passageway extending through said hollow body, said passageway having a gap extending entirely around said passageway and in a piane transverse to said passageway, a cathode for supplying electrons axially of said passageway past said gap, and means for collecting theelectrons after the passage of electrons'past said gap, insulating cup-shaped members closing the opposite ends of said passageway and providing with said hollow body an envelope for said cathode and collecting electrode, the outer surface of said hollow body being provided with an aperture and a reentrant extension oi' insulating material extending within said aperture and sealing said hollow body, and a conducting coupling member extending within the er'tmt insulating extension and said hollow 15. An electron discharge device including a hollow output tank circuit having a pair of coaxial tubular members spaced axially to forma gapand a conducting member surrounding said tubular members and conductively' secured to said coaxial tubular members, a cathode and grid positioned adjacent one end of one of said coaxial tubular members for supplying a modulated stream pf electrons axially of said coaxial tubular members across said gap and a collecting electrode adjacent an end of the other tubular member :for receiving the electrons from the cathode after passage across said gap and cupshaped insulating members closing the opposite ends of the coaxial tubular members to form with said hollow output tank circuit an envelope for said cathode, grid and collecting electrode, and a reentrant extension of insulating material extending within said aperture and said hollow output tank circuit and sealing said tank circuit, and conducting coupling means extending within the reentrant insulating extension.

16. An electron discharge device having a cathode for supplying a stream of electrons and means for collecting said electrons, a hollow tank circuit having a passageway extending therethrough through which the electrons from the cathode passto the collecting means, said passageway having a gap surrounding the discharge path between the cathode and the collecting means, means closing one end of the passageway to provide with the hollow tank circuit an envelope for the cathode, said hollow tank circuit having an aperture extending through the outer surface thereof, and a cup-shaped insulating closure member extending within said aperture and sealing said aperture in said hollow tank circuit, and a conducting coupling member withinthe hollow tank circuit extending through saidiaperture.

17. An electron discharge device having a cathode for supplying a stream of electrons and means for collecting said electrons, a hollow tank circuit having a passageway ,extending therethrough through which the electrons from the cathode pass to the collecting means, said passageway having a gap surrounding the discharge path between the cathode and the collecting means, insulating means closing one end of the passageway to provide with the hollow tank circuit an envelope for the cathode, said hollow tank circuit having an aperture extending through the outer surface thereof, and a reentrant insulating closure member extending within said aperture and sealing said aperture to said hollow tank circuit, and a, conducting coupling member within the hollow tank circuit extending through said aperture.

18. An electron discharge device having a cathode and grid for supplying a modulated stream of electrons and an electrode for co1- lecting said electrons, a hollow tank circuit surrounding said stream of electrons and having a gap lying in a plane transverse to the stream of electrons and between the grid and collecting electrode, and a pair of accelerating and screening electrodes positioned between the grid and the collector electrode,l one oi' the accelerating and screening electrodes being positioned on each side oi said gap.

` ANDREW V. HAEFF.

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