US2559524A - Electron discharge device of the beam deflection type - Google Patents

Description

y 3, 1951 .H. c. THOMPSON ELECTRON DISCHARGE DEVICE OF THE BEAM DEFLECTION TYPE Filed @012. 20, 1948 2 Sheets-Sheet 1 INVENTOR My C 790mm? July 3, 1951 H. c. THOMPSON ELECTRON DISCHARGE DEVICE OF THE BEAM DEFLECTION TYPE Filed Oct. 20, 1948 2 Sheets-Sheet 2 INVENTOR fizzy 6. Eomwv BY Z 71/ ATTORNEY Patented July 3, 1951 ELECTRON DISCHARGE DEVICE OF THE BEAM DEFLECTION TYPE Harry C. Thompson, Chester, Vt., assignor to Radio Corporation of America, a corporation of Delaware Application October 20, 1948, Serial No. 55,501

6 Claims. (01. 313-68) My invention relates to electron discharge devices, particularly to such devices employing electron beams subjected to varying transverse electric fields and employing secondary emission amplification.

In a beam deflection tube of the type described and claimed in a patent of William H. Warren No. 2,427,888, dated September 23, 1947, assigned to the same assignee as the present application, there is provided at one end of an elongated metal envelope a cathode assembly comprising a cathode and a cathode shield, both mounted be tween a pair of spaced insulators, preferably of mica, for providing a directed beam of electrons toward the other end of the envelope in which is positioned an anode or collector for receiving electrons. Between the cathode and the collector are provided a beam defining and deflecting electrode assembly, comprising a pair of spaced flat plate members having aperture-defining portions and a pair of oppositely disposed deflecting electrodes, and an intercepting electrode, the beam passing between the plate members and the deflecting electrodes and being directed on to the intercepting electrode and through an apertured secondary emission supperssor electrode to the anode. Electrons from the cathode are deflected across the intercepting electrode to produce an output current in the anode having an output frequency twice that of the alternating foltage applied to the deflecting electrodes. The entire electrode assembly is supported on a fiat metal closure memper sealing the metal enfelope and having an insulating insert through which leads from the. deflecting electrodes extend. It has been suggested that the anode be coated with emitting material to serve as a dynode for supplying secondary electrons when struck by the beam, and that these secondaries be collected by a separate apertured collector electrode provided in front of the anode for this purpose. The surface of the anode in said Warren patent is normal to the beam path.

In arrangements of the kind just described, secondaries often return to the vicinity of the intercepting wire or electrode and cause noise. In order to obtain greater emission of secondaries the usual practice has been to raise the accelerating voltages. and, hence, the speed of the electrons which strike the secondary emitting surface. This, however, reduces the life of the emitting surface. The described device is also subject to the objection that the degree of saturation of secondary current at all points of impact is not uniform due to non-uniformity of the elec- 2. tric field along the emitter and between the emitter and the collector. Where micas are used as the locators for the collector, space potential variations occur near the intercepting wire throughout its length which afiect the transit time of the components of the beam and thereby the effective transconductance of the device at high frequencies.

It is, therefore, an object of my invention to provide an improved form of electron discharge device of the type described.

Another object of my invention is to provide such a device utilizing secondary emission in which noise due to secondary electrons is minimized.

Another object of my invention is to provide such a device depending upon secondary emission amplification in which greater emission of secondaries is accomplished but at the same time favorable life is obtained.

A still further object of my invention is to provide such a device employing secondary emission amplification in which the degree of saturation of secondary current at all points of impact is made substantially uniform.

Another object of my invention is to provide such a device in which surface potential variations on insulating locators or spacers are substantially eliminated.

A still further object of my invention is to provide such a device in which the space potential near the intercepting wire is substantially constant throughout its length, thus improving the uniformity of the transit time of the components of the beam and thereby the effective transconductance of the device at high frequencies.

A principal object of my invention is to provide such an improved device in which the transconductance is increased several fold.

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 drawing, in which Fig. 1 is a side elevation with part of the envelope removed to show details of the mount construction; Fig. 2 is a section taken along the line 22 of Fig. 1; Fig. 3 is a transverse section taken along the line 33 of Fig. 1; Fig. 4 is an exploded perspective of the mount assembly shown and the method of assembly; and Fig. 5 is a diagrammatic longitudinal section and associated circuit of an electron discharge device made according to my invention.

Referring first to Figs. 4 and 5, particularly Fig. 5, the tube consists essentially of an elongated metallic envelope within which are mounted in order a cathode l heated by a heater I an apertured cathode shield l2, an accelerating and beam-forming electrode |3 comprising an apertured accelerating plate I4 and apertureforming plates l and I6, opposite deflecting plates l1 and I8 and an intercepting electrode I9, and an anode assembly comprising an apertured collector electrode and a secondary emitting electrode or dynode 2|. These elements are aligned along the longitudinal axis of the envelope I to define a thin beam path of rectangular section.

In accordance with my invention, the dynode 2| is inclined with respect to the beam path at a relatively small acute angle, preferably at an angle of about 30, and the collector electrode 20 is positioned closely adjacent the electrode 2| and parallel thereto. With the electrodes 20 and 2| inclined to the beam path at an acute angle. electrons passing through the aperture of the electrode 20 and striking the electrode 2| produce a greater amount of secondary these electrodes were arranged perpendicular to the beam path,and noise due to stray secondary electrons is minimized because the field between the inclined electrodes 2| and 20 is favorable to the collection of said secondary electrons by elec- 1 trode 20 rather than by electrode l9. secondaries which could otherwise return to the small interceptor wire |9 would perform orbits around it and, by. their presence in its vicinity, react upon the oscillating beam to produce an increment of noise.

The various electrodes of the tube are associated together and mounted within the envelope I in three connected assemblies, namely, a cathode assembly, a beam-defining electrode assembly, and an anode assembly, in a manner somewhat similar to that described in the aforesaid Warren patent.

Referring to Figs. 1 to 4, the cathode assembly includes the indirectly heated cathode ID, the cathode shield I2 having an elongated vertical aperture l2 and provided with positioning lugs l2". The accelerating plate |4 having an elongated vertical aperture l4 and positioning tabs or lugs I4" is also a part of the cathode assembly. These elements are spaced and supported between a pair of upper and lower insulating plates and 26, preferably of mica, and having appropriate apertures for receiving the ends of the oathode ||l and the positioning lugs l2" on the shield l2. The micas 25 and 26 are provided with deep notches 25' and 26 and notches 25" and 26 for purposes to be described.

The beam-defining and deflecting electrode assembly comprises the flanged aperture plates I5 and I6 of U-shape disposed on opposite sides of the beam path, the legs l5 and I6 of the plates extend parallel to the beam path. These aperture plates are separated by a pair of elongated conducting elements 21 and 28. The closed ends of the plates l5 and I6 are provided with outwardly directed deformations l5" and I6" to produce in effect a pair of apertures on either side of the deformed portions. The vertically-extendw ing deflecting electrodes l1 and I8 are supported between the legs of the plates l5 and I6. Each deflecting electrode assembly includes an insulating strip 30, preferably of mica, around which is folded a gold foil providing the deflecting electrode. A tab such as 3| receives the ends of each 75 sembly w th emission than if deflecting electrode for retaining the same in position and forproviding means to which terminals such as 32 and 33 may be attached. The deflecting electrode assemblies are secured to the legs l5 and |5' of the U-shaped plates l5 and I6 by straps 34 (see Figs. 1 and 4). The intercepting wire I! is supported between thelegs l5 and I6 and maintained in tension by means of a spring l9.

, The, anode assembly includes a pair of upper and lower metal locator plates 40 and 4| between which are mounted the vertically-extending collector 20 and dynode 2|. The collector 20 is preferably. an L-shaped sheet metal member the longer leg of which is provided with an elongated rectangular slot or aperture 20' near the base of the leg and with end flanges having notches 20".

The collector 20 is assembled between the locator plates 40 and 4| with the notches 20" registering with similar notches 40' and 4 therein as shown in the drawing and the flanges are welded to the plates. The dynode 2| and its insulating mounting is formed by assembling two channel-shaped elongated sheet metal members 36 and 31 with a mica strip 38 therebetween and welding the flanges together. The outer surface of the member 36 is coated with a good secondary emitting material. The mica strip 38 is longer than the members 36.and 31 and each end is made in the shape of a cross to provide means for positioning the members thereon and to'provide mounting lugs 33'. The dynode unit is mounted on the collector 20 with the secondary emitting surface facing the aperture 20' and the wall adjacent thereto and the lugs 38' extending through the notches 20", 40', and 4|, and is secured in place by strips 39 welded to the plates 40 and 4| across the notches 40' and 4|.

As stated above, the dynode 2| and preferably also the collector 20 are mounted at an acute angle of about to the electron beam path. For this reason, the plates and 4| are formed with the edges containing the notches 40' and 4| extending at the desired angle to the longitudinal axis of the plates. The opposite edges of the plates 40 and 4| are provided with deep notches 40" and 4|" adapted to receive the ends of the legs I5 and I6.

The cathode assembly and the anode assembly are assembled with the beam forming and deflecting electrode assembly, which last assembly may be referred to as the aperture frame, by inserting the ends of the frame into the notches 25' and 26' in the cathode assembly and the notches 40" and 4|" in the anode assembly. This automatically aligns all of the elements, that the cathode, the apertured elements, the apertures formed in the beam formingv assembly, the deflecting electrodes, intercepting wire, and the anode, since the elements in each assembly are positively fixed in definite spaced relation to each other and the notches automatically align the elements of the various assemblies. The assemblies are then looked together by means of an inverted U-shaped strap element which is welded to the top of the aperture frame, the legs of the U -shaped element 45 passing down through the notches 25" and 26" in the micas 25 and 28, and by welding the plates 40 and 4| to the legs I5 and I8 of the aperture plates. The legs of the U-shaped element are welded to the header 23 of the envelope thereby fixing the relative height of the mount assembly with respect to the header and the longitudinal position of the asrespect to the leads extending auaoas through the header. The anode assembly is secured to the header 23 by a pair of straps 46 and 41 welded to the header and to the lower plate 4| and leg 20" of the collector 20, respectively.

The cathode heater (not shown) is provided with a pair of leads 50 and 5|, the cathode I. with'a lead 52, and the cathode shield 12 with a lead 53, the leads being connected to terminals passing through the header 23 and sealed as shown by internal glass beads 54, 55, and 56. The shield I4 is welded to the strap 45 and thus electrically connected with the aperture frame, which is electrically connected to the intercepting wire I! and collector 20 and also to the metallic envelope l and header 23. The deflecting electrodes l1 and I8 are provided with leads 64 and 55 connected between the terminals 32 and 33 and terminals passing through the header 23 and sealed by glass beads 66 and 61. The dynode 2i is provided with a lead 68 and a terminal seal 69.

In Fig. 5 is shown a circuit including an electron discharge device made according to my invention. An input signal voltage may be introduced between the deflecting plates i1 and I8 by means of an input transformer and a local oscillator voltage by means of a transformer II. The output is taken by means of an intermediate frequency transformer 12. In the arrangement shown, the electrode l2, aperture plates I 5 and I6 and deflecting electrodes l1 and I8 provide an electron lens system for focusing the beam on the intercepting wire l9.

By placing the dynode at a relatively small acute angle to the beam rather than at right angles thereto, greater emission of secondaries is produced, noise due to stray secondaries is minimized, and the concentration of current at the region of impact is lowered thereby increasing the life of the emitting surface. Moreover, by grounding the collector to the intercepting electrode, aperture plates and envelope, and by placing the collector parallel and close to the emitter, the electric field along the emitter and between the emitter and collector is made substantially uniform resulting in the same degree of saturation of secondary current at all points of impact, and space potential variations near the intercepting electrode along its length and resulting transit time effects are substantially eliminated, thereby increasing the effective transconductance of the tube at high frequencies. An increase in transconductance of from 3 to 5 fold due to multiplication of the current delivered to the output electrode by use of secondary emission has been produced. Tubes have been made with transconductances from 2000 to 4000 micromhos.

The angle between the output electrodes and the beam is not critical but must be considerably less than 90 to produce the desired results described above, the 30 angle being a practical compromise. If the angle is made more acute the useful range of potentials is decreased, while if it is made less acute there is a loss in the advantages due to greater emission of secondaries and lower concentration of current at the region of impact. The plane of the aperture of the collector need not be the same as the collector surface, but instead, may be at right angles to the beam path.

In my co-pending application entitled Electron Discharge Devices of The Beam Deflection Type, Serial No. 55,502, filed October 20, 1948, concurrently herewith, I have disclosed and claimed several embodiments of a beam deflection tube having electrode structure similar in some respects to the electrode structure of the instant .application.

While I have indicated a preferred embodiment of my invention, it will be apparent that my invention is by no means limited to the exact form 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.

I claim:

1. An electron discharge device having electron gun means for supplying and directing a beam of electrons along a beam path, electrode means toward which said electrons are directed and including a first electrode having a secondary emissive surface extending across said beam path at a relatively small acute angle thereto, and. a second electrode positioned adjacent said first electrode and having an aperture through which said path lies, said second electrode having a collector surface facing and parallel to said secondary emissive surface, and means for deflecting said beam across said aperture.

2. An electron discharge device having electron gun means for supplying and directing a beam of electrons along a beam path, a first electrode having a surface extending across said beam path at an acute angle thereto, said surface having a coating of secondary emitting material thereon, a second electrode positioned adjacent said first electrode and having an aperture through which the beam path lies, said apertured electrode having a collector surface facing and parallel to the secondary emitting surface of said first electrode and an intercepting electrode having a transverse dimension less than that of said aperture and positioned in the path of said beam between said electron gun means and said second electrode, and 3 means for deflecting the electron beam across said intercepting electrode and said aperture.

3. An electron discharge device having electron gun means for providing a beam of electrons along a beam path, electrode means for receiving said electrons, and electrode means positioned between said electron gun means and said electron receiving means and through which the beam of electrons passes during operation of said electron discharge device and including a pair of oppositely disposed plate-like members spaced apart to provide a passageway therebetween, means on said plate-like members extending toward each other for restricting said passageway. said plate-like members having oppositely disposed arms extending therefrom toward said electron receiving means and deflecting electrodes supported from said arms on opposite sides of the beam path, said electron receiving means including an electrode having a plane surface extending across said beam path at an acute angle thereto and having a secondary emitting coating thereon, and a collector electrode adjacent the secondary emitting electrode and having an aperture through which the beam path lies, and means including conducting and insulating elements supporting said secondary emitting and collector electrodes, said supporting elements being secured tosaid arms at the free ends thereof.

4. An electron discharge device having electron gun means for supplying a beam of electrons along a beam path, a deflecting electrode assembly through which the beam path lies and including a pair of oppositely disposed plate-like members having oppositely disposed arms lying parallel to the beam path and deflecting electrodes supported by said arms on opposite sides of the beam path, and an output electrode assembly including conducting metal plate locators supported at the ends of said arms remote from said electron gun means, a collector electrode supported on said locators and comprising a sheet metal member having an L-shaped transverse section, said collector member having an aperture registering with the beam path, an electrode supported on said locators and having a plane surface of secondary 'emitting material registering with said aperture and said beam path, said secondary emitting surface lying at an acute angle to the beam path, said collector electrode having a plane collector surface parallel to said secondary emitting surface and closely spaced thereto, and an intercepting electrode positioned between said arms between said defleeting electrodes and said collector electrode. said intercepting electrode lying in the path of a the beam of electrons whereby the beam of electrons is deflected across said intercepting electrode and said aperture when operating voltages are applied to said deflecting electrodes.

5. An electron discharge device having an electrode assembly comprising a pair of oppositely disposed spaced members of insulating material, said members having a plurality of registering apertures therein, a first electrode supported between said pair of insulating members, the ends of said electrodes extending within said apertures, said members of insulating material having registering slots in one edge thereof, an electrode assembly comprising a pair of oppositely disposed substantially flat U-shaped elements, the closed endsof said u-shaped elements being received within said registering slots, an electrode assembly supported at the free ends of the legs of said U-shaped elements and comprising a pair of spaced parallel conducting locator plates secured to the free ends of said legs at each side of the U, a second electrode supported between said locator plates and having an elongated aperparallel to the secondary emitting surface of said third electrode.

6. An electron discharge device having electron gun means for supplying and directing a beam of electrons along a beam path, electrode means toward which said electrons are directed and including a first electrode having a secondary emissive surface extending across said beam path at an acute angle of about 30 thereto, and a second electrode positioned adjacent said first electrode and having an aperture through which said path lies, said second electrode having a collector surface facing and parallel to said secondary emissive surface, and means for deflecting said beam across said aperture.

1 HARRY C. THOMPSON.

REFERENCES crrnn The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,146,607 Van Overbeek Feb. 7, 1939 2,164,892 Banks July 4, 1939 2,205,055 ,Zworykin et al. June 18, 1940 2,323,729 Ryan July 6, 1943 2,390,701 Ferris Dec. 11, 1945 2,393,803 Nelson Jan. 29, 1946 2,427,888 Warren Sept. 23, 1947 2,434,713 Mueller Jan. 20, 1948

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