US2848636A - Anode structure - Google Patents

Description

Aug., 19, 1958 Filed Feb. 15. 1954 R. L. NORTON 2,848,636

ANODE STRUCTURE 2 Sheets-Sheet l INVENTGR. ROBERT L. MORTO .ATTORNEY Aug. 19, 195s Filed Feb. l5, 1954 R. L. NORTON ANODE STRUCTURE 2 Sheets-Sheet 2 INVENTOR. ROBERT L. NORTON l ATTRMEY United Sftates Patent C ANODE STRUCTURE Robert L. Norton, Santa Barbara, Calif., assignor to Penta Laboratories, Inc., Santa Barbara, Calif., a corporation of California Application February 15, 1954, Serial No. 410,126

4 Claims. (Cl. 313-40) This invention relates to an anode for electron discharge devices and more particularly to an anode having a large radiating surface with minimum heat transfer by conduction.

In the operation of a vacuum tube, the difference between power input and power output appears primarily as heat energy at the plate or anode of the tube. Since unduly high temperatures shorten tube life, it is of utmost importance that the heat energy thus formed be eciently radiated away from the anode in order to obtain high power output with long tube life.

An expedient adopted in the prior art for increasing the heat radiating area of radiation cooled anodes involves adding ns or projections to the outer surfaces thereof. The heat energy, however, is actually produced by the action of the electronics arriving at the inner surface of the anode, so that the heat must pass through and along the anode by conduction and thence to the fins, also by conduction, before any radiation can take place from the fins. Unfortunately, most of the metals in common use as anode materials, such as molybdenum and. tantalum, for example, have relatively poor heat conduction properties, and as a consequence, the fins must be spaced close together to minimize the occurrence of hot spots on the anode surface itself. Even with closely spaced ns the anode surface temperature is.invariably higher than that of the ns. Anodes with closely spaced tins are difficult and costly to fabricate.

In the instant invention, a simple, easy to manufacture anode is described in which the effective area for heat radiation is large, and in which the distance for the heat to travel by conduction before it is radiated away is small at all points on the anode.

In one embodiment the anode comprises a corrugated or otherwise distorted sheet as an electron collector and heat radiating surface for use in conjunction with other tube elements in a tube in which the distortion of the electric field in the proximity of the corrugated anode surface either is not detrimental to the proper operation of the tube or can be employed to obtain improved tube characteristics such as remote cutoff. Typical cases in which the field shape immediately in front of the anode is of little consequence are diodes withV relatively large anode-cathode spacing, and high mu triodes. In multigrid tubes, such as tetrodes and pentodes, the distortion of the field immediately in front of the anode may readily be made of no consequence by proper tube design.

In another embodiment of the invention the anode comprises a corrugated or otherwise distorted sheet for electron collection and heat radiation and having an equipotential surface provided on the side of the anode facing the cathode by a fine mesh, or grid, mechanically secured to portions of the anode and forming an electrical surface of desired shape. The mesh establishes an equipotential surface and at the same time functions as a sieve with respect to electrons, letting them pass through to the anode. This type of construction is advantageous in tubes in which an anode potential surface firice different than that which can be provided by a distorted anode surface is required for proper tube operation.

An object of this invention is to provide an electron tube having improved anode electrode with a large, uniformly heated radiating area.

A further object of the invention is to provide a rigid, easily fabricated anode having uniform heat transfer over an extended area.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following description.

Fig. l is a perspective view, partly in cut-away section, of a vacuum tube having an anode embodying the invention and shown in relation to the elements with which it is used;

Fig. 2 is a perspective View of an anode showing details of construction;

Fig. 3 is a perspective view of a form of anode embodying the invention and adapted for use in -assemblies wherein the uncorrected distortion of the potential resulting from the distorted anode shape can not be tolerated for proper tube operation; and

Fig. 4 is a perspective view of the elements of a vacuum tube having an anode adapted for use in a tube of plane,

rather than cylindrical, geometry.

The tube shown in Fig. l includes a glass envelope 10, a base l2, and mounting prongs 14. Anode 16, which is cut away to show other tube electrodes, is secured to lead 18 by means of bracket 20, and the anode lead is sealed through the envelope to make a connection with anode connector 22. Screen grid can 26 supports an elongated screen grid 28, and is connected to one of the mounting prongs 14. The screen grid is centered around a control grid 29 which in turn surrounds a cathode 30. Hat 31 is secured to the top of the anode to protect the dome of envelope 10.

In the operation of the tube, electrons are emitted by the cathode and start toward the anode. The control grid exerts a control action in the normal manner and the screen grid, being positive, attracts the electrons. The screen grid, however, has a small frontal area, and the wires forming it are customarily aligned with the wires of the control grid so that most of the electrons pass through the screen grid and are collectedl on the anode. Over the range in which a tetrode is designed to operate, the current to the anode is determined almost entirely by the grid and screen voltages. Changes in anode voltage or changes in the location of the anode will bring about practically no change in anode current. Similarly.A changes in the anode shape have little effect on the anode current. Electrons moving through the screen grid pass in relatively straight lines to the anode, causing the sides and bottoms of the anode recesses to be heated as much as the innermost projections of the anode thus bringing about nearly uniform heating of the entire anode surface.

Anodes constructed according to the present invention show a uniform color over the entire surface when in operation. Generally similar tubes operated under the same conditions and having the same cooling area but including tubular anodes with radial cooling ns Iconstructed in accordance with methods known in the prior art exhibit areas having temperature differences; areas between ns glow brightly while the ns and immediately adjacent areas thereto are much darker. The advantages of having uniformly cooled anodes with large radiating areas are obvious since tubes incorporating such anodes can be safely operated at much higher output levels than tubes constructed in accordance with previously known techniques,

The configuration of the pleated Ianodes provides an additional benefit in the operation of tetrodes in that secthe recessed portions of a corrugated anode, on the other.

hand, many of the secondary electrons knocked off the surface do not escape from the recesses formed by the pleating and they are eventuallyY collected by the anode. This reduction in the number of secondary electrons which are collected by the screen grid is demonstrable on measuring equipment and, has the effect of displacing thek region in which the plate current levels .olf in curves prepared by plotting plateV current`Y against plateI voltage. Since the bend or knee in the curves thus obtained occurs atlower plate voltages, tubes having'anodes constructed in accordance with the teachings of this disclosure may be operated with lower plate voltages'than tubes including tubular anodes. y

The anode shown in Fig. 2 is preferably constructed from a strip of refractory metal such as molybdenum or tantalum. The material may be corrugated or pleated between mating rolls, or stamped out by dies, ,or the crimps may be made individually. The two ends of the stripV are preferably joined by welding as shown at point 32..' Ring 34, which is made of a refractory metal, is joinedv to the inner points of -the crimped anode by welding; the structure is very stiff and rigid since the individual projections or radially extending serrations function as reinforcing members which vresist distortion in any plane. A second ring is similarly 'secured to the other end of the anode.Y In a typical anode, about 13 inches of molybdenum one and one-half inches wide and about 5 mils thick is crimped or folded to have 1'6 pleats ofV about one and three-fourths inches and a minimum diameter across inner points of opposing pleats of about one inch. Anodes constructed according to the above dimensions have been found to easily handle a plate dissipation of over 400 Wattsin radiation cooled tetrodes. While the structure shownin Fig. 2 has many advantages such as extended surface area,rrigidity, ease of construction, and good heat dissipation properties, itwill be understood that anodes having corrugations in other directions or having, for example, dimpled surfaces, function in the same manner and for the same reasons as the illustrated form of the invention.

'I'he assembly shown in Fig. 3 comprises a crimped anode similarv to that shown in Fig'. 2 but with the addition vof a Wire mesh cylinder 40 in the interior of the anode. The mesh establishes an equipotential surface which at the same time functions as a sieve with respect to electrons, letting them pass through yto the anode. Since all surfaces of the anode are at exactly the same potential as the mesh, the voltage gradients in the areas between the mesh and the recesses in the anode are extremely slight land the electronsshow no tendency to focus on any particular contour or point. The sizes of the -openings in the mesh should be as large as possible, but must not be so large as to fail to produce the desired electrical surface. The maximuntmesh size -is dictated by the electrode spacings and the size of the recesses in the anode. In general, the required mesh opening size is decreased by close electrode spacings or large anode recesses. The wires forming the mesh must be small so they will intercept a -minimum number of electrons. It has triode of cylindrical geometery having a corrugated anode with an inside diameter of about one inch "and with about 16 corrugations, each three-eighths of an inch deep. The assembly may be fabricated by forming a corrugated or crimpedv anode in any desired manner and welding the wire mesh to the inner projecting points of the anode.

The structure shown in Fig. 4 includes an electrode support 44 which maintains plane cathode 46 in position,

and support 48 which similarly positions control grid 50.`

Anode 56 consists of an inverted V-shaped metal .strip having a grid 58 consisting of a series of parallel wires bridging the open end of lthe V-shaped strip. Grid V58 across the anode opening establishes an effective plane electrical anode surface at the desired vpoint whileat the same time allowingmost of the electrons to pass through and give up their energy in the form of heat at the large heat radiating anode surface. The advantages of this type of tube in which large radiating surfaces are obtainable while keeping the direct capacitance fromrthe anode. to other electrodes at a minimum are obvious. Grid 58V across the anode opening may be either bars, as shown, or a mesh; in special purpose tubes wherein a curved potential field in front of the anode Lis desirable, the grid or mesh maybe eliminated entirely. Anode 56 is supported by lead 60.

' Obviously, many modifications and variations of the present invention are possible in the light of the above been found that a mesh comprising 0.001 to 0.005 inch teachings.

the scope of the appended claims the invention may be practiced otherwise than as specifically described.

Whatis claimed is: .A 1. A thin walled extended area anode for a triode comprising akmetallic endless corrugated strip,k and a wire mesh secured to and in electrical contact with the innermost points of the corrugations in said strip. K

2. An electron tubecomprising an evacuated envelope, a planar cathode mounted in said envelope, a planar control grid disposed adjacent and parallel to said cathode, a Vnonplanar anode positioned adjacent said screen grid, and a planar anode-grid secured to and in electrical contact with said anode and establishing a planar effective anode parallel to said control grid.

3. In a vacuumtube having at least a cathode and an anode thecombination of: said anode formed of corrugated conductive material to form first portions of the anode closer to the cathode of the tube than second portions of the anode; and a conductive wire mesh connected to said first portions of the anode and positioned and arranged between the second portions of the anode `and th cathode.

Y 4. In a vacuum tube having yat least a cathode and an anode the combination of: said 4anode formed of corrugated conductive material to form lirst portions of the yanode closer to the cathode of the tube than second portions of the anode; and a cylindrical conductive wire mesh connected to the inside edge of each of the first portions of the anode and positioned and arranged to circumscribe the cathode.

References Cited in the le of this patent UNITED STATES PATENTS 1,437,607 Mueller Dec. 5, 1922 1,704,155 Thomas Mar. 5, 1929 1,920,649 Lederer Aug. 1, 1933 2,042,951 Marden June 2, 1936 2,071,696V lonas Feb. 23, 1937 2,081,714 Rotheet al. May 25, 1937 2,115,934 Smith May 3, 1938 2,136,610 Colby Nov. 15, 1938 2,648,793 Wihtol Aug. 11, 1953 It is therefore to be understood that within

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