US2909690A - Beam type tube - Google Patents

Description

IMIHHHH BEAM TYPE TUBE M. E. LEVIN ETAL Filed Oct. 25, 1957 Oct. 20, 1959 niteci States Patent BEAM TYPE TUBE Martin E. Levin, Millbrae, Anthony S. Wolfson, Palo Alto, and James I. Young, Burlingame, Calif., assignors to Eitel-McCullough, Inc., San Bruno, Calif., a corporation of California Application October 23, 1957, Serial No. 691,819

9 Claims. (Cl. 313-82) This invention relates generally to a beam-type tube, and more particularly to a beam switching tube.

It is a general object of the present invention to provide a beam-type tube suitable for operation at relatively high voltages and currents.

It is another object of the present invention to provide a beam tube for switching high voltages and passing relatively high currents.

It is another object of the present invention to provide a tube of the above character which has relatively low tube drop and low drive power. v

It is another object of the present invention to provide a tube of the above character in which the various electrodes are so arranged that the tube is capable of withstanding relatively high voltages.

It is another object of the present invention to provide a tube of the above character which is of stacked metal and ceramic construction and in which the parts are symmetrically arranged.

It is another object of the present invention to provide a beam tube of stacked metal and ceramic construction in which the metal terminal assemblies are formed to present smooth surfaces to one another.

The invention possesses other objects and features` of advantage, some of which with the foregoing will be set forth in the following description of the invention. It is to be understood, of course, that the inventionis not to be limited to the disclosure of a particular species of the invention, as other embodiments thereof may be adapted within the scope of the claims.

Referring to the drawing:

Figure 1 is an elevational view, partly in section, of a beam tube in accordance with the invention;

Figure 2 is an end view of the tube of Figure 1; and

Figure 3 shows the constant voltage characteristics of a tube constructed in accordance with the invention.

The tube has an evacuated gas-tight envelope of generally cylindrical stacked metal and ceramic construction.

The tube (Figure 1) includes an electron gun 11 which serves to project a beam of electrons which are collected by the collector 12.

The electron gun 11 illustrated includes a cathode vwhich is in the shape of an oxide coated nickel dish `14 prepared for emission in a well known manner. The dish 14 is indirectly heated by the filament 15. A cylindrical focus electrode y16 surrounds the dish and shapes the electronvbeam. An anode 13 is interposed between the cathode and the collector 12 and serves to laccelerate and modulate or control the electron beam.

Terminal ring 17 forms a portion of the base of the tube and provides a lead-in to the focus electrode of the electron gun 11. A seal 18 is made between the ring 17 and `an adjacent ceramic ring (not shown). Terminal ring 19 provides a lead-in lto the cathode. Terminal ring 21 provides a lead-in to one filament (heater) terminal. The other filament terminal is connected to the cathode. j

The lower wall portion of the cylindrical envelope in- ICC cludes the stacked ceramic rings 22 and 23, and terminal assemblies 24, 26 and 27. The ceramic rings are preferably of high refractory material such as alumina and are metallized at both ends by suitable metallizing procedures such as by molybdenum manganesev powder sintering process. The terminal assembly portions have high electrical conductivity. For example, the terminal assembly may be made of copper. The sandwiched parts are brazed together using high temperature brazing alloys. The metal bonds at the brazed joints form strong mechanical connections and provides a vacuum seal so that the side alls of the envelope form a solid impervious cylinder of rugged construction. The terminal assemblies provide desired lead-in conductors through the'envelope to the interior electrodes.

One end of the cylindrical ceramic ring 22 is suitably sealed to the terminal assembly 24 which makes electrical connection ywith the collector 12. The terminal assembly includes a terminal 28 which is suitably brazed to the portions 29 and 31 of the collector. A sealing ring 32 is brazed at one end to the terminal ring 28. A sealing ring 33 is brazed at one end to the ceramic ring 22 and to the ceramic backing ring 34. The sealing rings 32 and 33 are curved outwardly and have their ends curved back toward the associated terminal 28. The adjacent ends of the sealing ring are bonded 36 to form a vacuum tight seal. The curved configuration provides a seal which does not occupy substantial axial distance, and presents a smooth surface to adjacent terminal assemblies, as will presently become apparent. An opening 37 is formed in the terminal ring 28. rThe opening serves to connect the space between the sealing rings to the interior of the tube envelope. This relieves pressure which might be built up in this space when the tube'is placed in an oven to braze together the various parts forming the envelope. A terminal ring 43 is provided for making electrical connection to the anode 13. The ring is supported be tween the ceramic rings 22 and 23 by a pair of terminal Vassemblies 26 similar to that previously described. Thus, the seal includes sealing rings 38 and 39 each having one end brazedto the adjacent ceramic rings 22 and 23, respectively, and to the ceramic backing rings 41 and 42, respectively. One end of the sealing 4rings 44 and 46 is brazed to the terminal ling 43. Again, the sealing rings are curved outwardly and their ends are bent back toward the associated terminal. The free ends are bonded as indicated at 47 and 48. An opening 49 is provided in the .terminal ring 43 to connect the space between sealing rings with the interior of the envelope whereby pressure is not built up lwhen the various parts are brazed together.

A suitable seal assembly 27 is secured to the other end of the ceramic ring 23 and serves to form another seal. The seal assembly 27 is similar to those previously described and includes a terminal member 17, previously described, a sealing ring 51 which has one end brazed to the ceramic ring 23 and to the backing ring 52, and a sealing ring 53 which is brazed to the terminal ring 17. The sealing rings 51 and 53 are curved outwardly and towards the terminal and bonded at 54. An opening 56 connects the space between rings with the interior of the envelope for purposes previously described.

The sealing rings for each of the terminal assemblies are curved outwardly and toward the associated terminal. This curved configuration occupies a minimum axial space, thereby increasing the separation between the sealing rings of adjacent assemblies for a tube of given are curved outwardly and towards the associated terminal present smooth surfaces to adjacent terminal rings. This eliminates the possibility of field concentrations at sharp corners and reduces the likelihood of corona and arcing. The increased spacing and reduction of eld conccntration provides a tube in which relatively high voltages can be applied between electrodes.

The collector illustrated has a cylindrical envelope portion 29 previously described, and a bell shaped portion 3l. The two portions 29 and T11 are suitably brazed to the terminal ring 2S. The portion 3i has a planar portion 6l which is provided with an opening e2 through which the electron beam passes. The opening 62 is tapered outwardly as indicated at 63 and polished.

A plate 64 is secured to the other end of the cylindrical portion 29 of the envelope and carries the tubulation 66 which is protected by a cap 67. lt is to be noted that the tubulation is placed olf center whereby the electron stream does not bombard the tubulation to damage the same.

The collector which completes the electronic circuit is the fly-trap type comprising a large cylindrically enclosed volume presenting a relatively small escape aperture 62 to secondary electrons.

The anode i3, wbch comprises an annular metallic member 7i and a cup-shaped skirt 72, serves the function which is normally performed by a grid in a conventional tube, but is not a grid. ln fact, there is nothing in the tube which resembles the normal mechanical configuration of a grid. There are several advantages accruing from this feature. The propensity of fine gri wires towards mechanical instability is completely eliminated by the heavy construction used here. The large radius aperture lips 73 prevent field concentrations which might lead to arcing within the tube to a much greater extent than would a grid wire. The mass of this electrode is capable of dissipating large amounts of heat created by overload circuit, misadjustment, or improper operation, without detrimental effects.

ln operation the electrons from the cathode i4 are focused into a beam which is of smaller diameter than the diameter of the opening of the annular member 7l of the modulating anode i3. The length of the annular member' 7l is such that the modulating anode acts as an electrostatic shield between the collector l2 and the cathode i4. Thus, the electrons at the cathode surface are substantially unaffected by the potential difference between the cathode and the collector. lf a slight positive potential is applied to the modulating anode i3 with respect to the cathode la the electrons at the cathode surface will be accelerated toward the modulating anode. However, such electrons will be prevented from reaching the modulating anode i3 due to the focusing action of the gun il, and will pass through the opening in the annular member 71 of the modulating anode and through the aperture o2 and into the collector 12. Thus, the beam current between the cathode M and the collector l2 may be controlled by varying the potential difference between the modulating anode i3 and the cathode, maximum beam current being obtained when the potential of the modulating anode approaches a potential more positive than the potential of the collector with respect to the cathode, and minimum beam current being obtained as the potential of the modulating anode approaches zero with respect to the cathode. The focusing action of the gun 1i iS such that essentially no electrons are intercepted bythe modulating anode unless the potential between the modulating anode and the cathode exceeds the potential between the collector and the cathode as will be explained hereinafter. Thus, not only are there no grid wires, but also there is essentially no grid current in normal operation. In addition, the modulating electrode protects the cathode surface from reverse ion bombardment and arcing under most operating conditions.

The shapes of both the annular metallic member 71 f the modulat"ry anode and the aperture 62 of the collector are determined by their respective functions in the operation of the electron tube. Since Ithe operation of the tube requires high voltages between the collector 12 and the anode f3 the problem which then arises is that of mounting the electron active portions 62 and '7l thereof and insulating such portions from each other so that the highest possible breakdown voltage therebetween is obtained. The problem resolves itself into first, the shape of the support members for each of such electron active portions 62 and 7l and, second, the positioning of the insulating member between such supports.

It is known that, given any two electrodes regardless of their shape with a potential difference therebetween, an electric field will be distributed between the two electrodes and that such distribution is usually represented by equal potential lines, each representing in cross section a piane or surface at which a certain percent of potential between the two electrodes will appear. For example, a line may be plotted which will represent in cross-section that surface at which 50 percent of the voltage between the two electrodes will appear. in order for the maximum voltage breakdown to be exhibited in a structure comprising two electrodes separated by an insulating member, the 5() ercent of the voltage between the two electrodes will appear. In order for the maximum voltage breakdown to be exhibited in a structure comprising two electrodes separated by an insulating member, the 5G percent equal potential surface mentioned above should coincide with the center plane of such insulating member at least at outer surface of such insulating m er and the voltage gradient between the ends of the in ulating member should be uniform. lf the surface of SO percent equal potential is not a flat plane but rather an irregular surface it may be extremely' difficult to accomplish these objectives. However, if the two electrodes and their supports are mirror images of each other'the 50 percent equal potential surface will be a flat plane and will occur half way between the electrodes. Thus, when one electrode and its support are a mirror image of the other' electrode and its support, the matching of the 5t) percent equal potential surface to the center plane of an insulating member which separates the electrodes is comparatively simple. Referring to Figure l it will be seen that an effort has been made in the structure of a tube according to the subject invention to provide electrodes and supports which are mirror images of each other. Obviously the symmetry is somewhat marred by the fact that the shape of the electron active portion 71 of the anode i3, in order for it to perform its function as a control member, is somewhat different from the shape of the electron active portion of the collector electrode 12 comprising generally the aperture 62. Therefore, only the skirt 72 of the anode 13 and the portion 31 of the collector 12 can be mirror images of each other. However, it has been found that with the structure shown the 50 percent equi-potential surface will intersect the outer periphery of cylinder 22 midway between the ends of the cylinder.

The above mentioned structural considerations coupled with the arcuate shape of the seals hereinabove described makes possible the high voltage stand-off characteristics of the tube constructed in accordance with the subject application. Since the Voltage gradient is substantially equally distributed along the length of the ceramic cylinder 22 arcing will occur only when the voltage has reached a value capable of ionizing the medium exteriorally of the envelope between terminals 33 and 38 and thus producing an arc therebetween.

The tube described and illustrated is preferably operated by immersing the same in an oil bath, thereby increasing the breakdown voltages. Generally, the tube may be operated in oil at about two times the voltage rating for air.

Figure 3 illustrates the characteristics of a typical electron tube according to subject invention which make it desirable for use as a switch tube. In the graph shown in Figure 3 the beam or collector current is plotted along the vertical axis and the collector voltage is plotted along the horizontal axis, the cathode voltage being zero. Curves are shown for several different values of modulating anode voltage. It will be seen that with a given voltage on the modulating anode the beam' or collector current remains substantially constant over a Wide range of collector voltages (eg. from 1 kv. to 60 kv. on the graph). In other words, for a given voltage on the modulating anode with respect to the cathode the current passing through the tube will remain substantially constant regardless of the voltage drop across the tube. y Thus an electron tube according to the subject invention has an advantage over other types of switch devices in that it is capable of controlling the amount of current which Will flow through it substantially independently of the voltage applied across it. For example, if 1.25 amperes are required in a particular circuit, approximately 6 kv. should be applied to the anode 13. rWhen the 6 kv. is applied to the anode, the tube will conduct approximately 1.25 amperes regardless of the voltage between the collector and cathode over a wide range (e.g, 1 kv. to -60 kv.). However, if the voltage between the collector and the cathode becomes too low (e.g. below 1 kv.) so that the collector becomes too negative with respect to the anode, electrons'will begin to be attracted away from the collector and will be collected by the anode instead. If this happens the voltage on the anode will be reduced resulting in a corresponding reduction in current ow to the collector which in turn tends to cause an increase in collector voltage. An increase in collector voltage will reduce the number' of electrons which return to the anode which will tend to produce an increase in anode voltage. Thus, it will be seen that an equilibrium point will be reached which point will be determined by the circuit in which the tube is to operate. Therefore, a tube according to this invention has the still further advantage of being capable of automatically adjusting the current flow in a circuit to lmeet the requirements of the circuit.

For example, let us assume that it is desired to charge a given capacitance to approximately 60 kv. in a particular time interval and to maintain such charge constant for a given time interval regardless of leakage losses in the capacitance. A tube according to the subject invention is connected in series with the capacitance across a 60 kv. supply and the proper voltage is applied to the anode to provide the current ow required to charge the capacitance in such selected time interval. `The current ilow will remain substantially constant regardless of the fact that the voltage across the tube will decrease as the charge on the capacitance increases. Furthermore, when the charge on the capacitance has reached substantially full value, electrons will not reach the collector but will return to the anode, lowering the voltage thereon and decreasing the current ilow to the collector. This action will continue until the current ow through the tube matches the leakage current ow through the capacitance thus maintaining the charge on the capacitance constant regardless of the leakage current low.

Thus, it is seen that a beam switch tube capable of widely diversified applications lhas been provided. 'The constant current characteristics and the ability of the tube to reach current ow equilibrium for a given circuit are particularly desirable. In addition the tube is especially desirable where mechanical and thermal endurance, simplicity, high voltage capacity and low tube drop are required characteristics. As pointed out hereinabove, very little power is required to control the tube since a minimum of electrons are intercepted by the anode due to the beam nature of the current flow through the tube.

It is to be understood, of course, that the invention is not limited to a switch tube. For example, the tube may bel operated as an ampliler in which the modulating anode serves to modulate the electron beam in accordance with an input signal.

.Having thus described the invention what is claimed as new and desired to be secured by Letters Patent is:

1. A beam-type tube comprising an electron gun serving to project a beam of electrons, said gun including a cathode and an anode structure, a collector disposed to receive said beam, said collector comprising an enclosed volume having an opening slightly larger than the electron beam through which the beam passes to be collected, a terminal assembly for making electrical connection to the collector, a terminal assembly for making electrical connection to the anode, and an insulating cylinder coaxially surrounding said collector and said anode, one end of said insulating cylinder being hermetically sealed to said terminal for said anode and the other end of rsaidrinsulating cylinder being hermetically sealed to said terminal for said collector, the center plane of said insulating cylinder coinciding with the fifty percent equipotential plane between said anode and collector at the outer boundary of said insulating cylinder.

2. A beam type tube comprising an electron gun serving to project a beam of electrons, said gun including a cathode, focusing electrode, and anode, said anode comprising an annular member through which said beam is projected, a collector disposed adjacent said anode to receive said beam, said collector comprising an enclosed volume having an opening slightly larger than the electron beam and through which the beam passes to be c0-llected, a terminal assembly for making electrical connection to said collector, a terminal assembly and support for making electrical connection to said anode, said support and terminal for said anode having a surface which is substantially a mirror image of the adjacent surface and terminal of said collector.

3. A beam-type tube comprising an electron gun serving 'Ato project a beam of electrons, said gun including a cathode and an anode structure, a collector disposed to receive said beam, said collector comprising an enclosed volume having an opening slightly larger than the electron beam through which the beam passes to be collected, a terminal assembly for making electrical connection to the collector, a cylindrical envelope portion secured to said terminal assembly, a second terminal assembly secured to the opposite end of said cylindrical envelope portion and serving to support the anode, adjacent portions of the anode support and collector being shaped substantially symmetrical with respect to opposite sides of a plane intersecting the envelope portion at its center and perpendicular to the longitudinal axis of the tube.

4. A beam-type tube comprising an electron gun serving to project a beam of electrons, said gun including a cathode and an anode structure, a collector disposed to receive said beam, said collector comprising an enclosed volume having an opening slightly larger than the electron beam through which the beam passes to be collected, a terminal assembly for making electrical connection to the collector, a cylindrical envelope portion secured to said terminal assembly, a second terminal assembly secured to the opposite end of said cylindrical envelope portion and serving to support the anode, said modulating anode terminal assembly and adjacent portions of the collector being so shaped that the fields which intersect the envelope portion are relatively uniform, said anode and collector being arranged substantially symmetrical with respect to opposite sides of a plane intersecting the envelope portion at its center and perpendicular to the longitudinal axis of the tube.

5. A beam-type tube comprising an electron gun serving to project a beam of electrons, said gun including a cathode and an anode structure, a collector disposed to receive said beam, a cylindrical envelope portion, a terminal assembly for making electrical connection to the collector sealed to one end of said envelope portion, said terminal assembly including a terminal ring connected to said collector and sealing rings serving to form a seal between said envelope portion and said terminal ring, a second terminal assembly secured to the opposite end of said envelope, said second terminal assembly including a second terminal ring connected to said anode and sealing rings forming a seal between said envelope portion and said Second terminal ring, said sealing rings associated with said first and second sealing assemblies being curved outwardly and having their end portions curved back towards the associated terminal whereby they occupy a minimal axial space and present curved surfaces to adjacent terminal assemblies.

6. Apparatus as in claim wherein said anode and adjacent portions of the collector are arranged substantially symmetrical with respect to opposite sides of a plane intersecting the envelope portion at its center and lying perpendicular to the longitudinal axis of the tube.

7. A beam-type electron tube comprising an electron gun serving to project a beam of electrons, said gun including a cathode, a focus electrode, and an anode structure, said anode structure comprising an annular member mounted in an aperture at the bottom of a cupshaped support member, said cup-shaped support member opening toward said cathode, a terminal assembly for said anode electrically connected to the edge of said cup, a collector for receiving said beam of electrons, said collector including a cup-shaped portion having an aperture in the bottom thereof, and a terminal assembly connected to the edge of said cup-shaped portion, said cupshaped anode support member and said cup-shaped collector portion being mounted adjacent each other in reverse orientation with said aperture in said collector portion aligned with said annular member of said anode structure, the adjacent surfaces of said cup-shaped support member and said collector portion having substantially the same shape, and a cylindrical envelope member of insulating material coaxially surrounding said cupshaped support member and said cup-shaped collector portion and having its ends sealed to said terminal assemblies.

S l 8. A beam-type tube comprising an electron gun serving to project a beam of electrons, said gun including a cathode and an anode structure, a collector disposed to receive said beam, a terminal assembly for making electrical connection to the collector, a cylindrical insulating envelope portion secured to said terminal assembly, a second terminal assembly secured to the opposite end of said cylindrical envelope portion, a supporting member attached to said second terminal assembly and making electrical connection to the modulating anode, said anode supporting member and terminal assembly forming sub,- stantially a mirror image of the adjacent surface of said collector and said collector terminal assembly.

9. An electron tube comprising a plurality of electrodes contained within an evacuated envelope, said envelope comprising a ceramic cylinder forming a portion of the side wall thereof, a iirst terminal ring assembly sealed to one end of said ceramic cylinder and electrically connected to one of said electrodes, a second terminal ring assembly sealed to the other end of said cylinder and electrically connected to another of said electrodes, said terminal assemblies each comprising a terminal ring and a pair of sealing rings, one ring of each of said pairs being sealed to said cylinder and the other ring of each of said pairs being sealed to its respective terminal ring, said sealing rings being curved outwardly away from the cylinder and having their ends bent back towards the associated terminal ring whereby said sealing rings occupy a minimal axial space, said pairs of sealing rings presenting curved surfaces toward each other, and the rings of each pair being tted into each other and hermetically bonded together.

References Cited in the file of this patent UNITED STATES PATENTS 1,074,449 Myers Sept. 30, 1913 2,464,229 Hansen Mar. 15, 1949 2,480,133 Hansen Aug. 30, 1949 2,538,267 Pierce Ian. 16, 1951 UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No, 2,909,690 October 20, 1959 Martin Ea Levin et al.

It is hereby certified that error of the above numbered patent requiring Patent should read as corrected below.

appears in the printed specification correct-ion and that thesaid Letters Column 2, line ll, for nprovidesn read provide mi; line' l2, for "alle" read -fwalls uw; column 4, line 2l, beginning with "In order for the maximum voltage" strike out all to and including "appear," in line 25, same eolumn Signed and seal-ed this 19th day of April 1960.

(SEAL) Attest:

KARL Hf, AXLINE ROBERT C. WATSON Attesting Ufficer Commissioner of Patents

Images