US2573397A - Mount for electron discharge devices - Google Patents

Description

1951 D. G. BURNSIDE 2,573,397

MOUNT FOR ELECTRON DISCHARGE DEVICES Filed June 9, 1949 2 SHEETSSHEET 1 INVENTOR N G BURNSIDE WMKK Oct. 30, BURNSIDE v MOUNT FOR ELECTRON DISCHARGE DEVICES Filed June 9, 1949 2 SHEETS-SHEET 2 INVENTOR DON G. BURNSIDE Patented Oct. 30, 1951 DEVICES Don G. Burnside, Princeton, N. 1., assignor to Radio Corporation of America, a corporation of Delaware Application June 9, 1949, Serial N0. 97,936 11 Claims. (c1. 313 -296) The present invention relates to electron discharge devices, and more particularly to mounts for such devices suitable for use .at ultra high frequencies.

Some ultra high frequency electron discharge devices include four electrodes comprising a cathode, a control grid surrounding the cathode, a screen grid surrounding the control grid, and a tubular anode surrounding the screen grid. In some .instances beam forming plates have been employed between the screen grid and the anode. When electron discharge devices are operated at ultra high frequencies, the grid-plate trans.- conductance is usually reduced because of what has heretofore been regarded as unavoidably high input and output capacitances.

Factors which have been recognized as contributing to high input and output capacitances of such devices include spacings between the electrodes, the magnitude of the surface areas of the cathode and anode, and the cross sectional size of the leads.

It has been recognized that the employment of a cathode having a relatively large emitting area in association with a control grid spaced very closely with respect thereto, contributes to an increase in grid-plate transconductance with consequent high amplifications at high frequencies. But attempts heretofore made to closely space conventional control grids and cathodes have resulted in increasing the input capacitance of the device, with consequent low input impedance and low amplification at high frequencies. It has also been recognized that a relatively close spacing between the control and screen grids is advantageous in securing high grid-plate transconductance. But here again the use of conventional grids has defeated the object sought. One major cause for failure to secure good results with conventional grids is the fact that temperature changes in the grids cause some displacement thereof which is sometimes suflicient to bridge the spacing between the grids and between the control grid and the cathode. Another reason for failure of conventional grids to contribute to high grid-plate transconductance is the fact that the grid side rods usually used to support the grid wires, produce objectionable capacity effects.

A further contributing factor to a reduction in grid-plate transconductance is capacity effects between portions of the electrodes extending through and beyond insulating spacers sometimes used to space the electrodes from each other. Where such spacers are employed it is customary to support the electrode assembly between two of such spacers and it is extremely diflicult to prevent portions of the electrodes from projecting from the outer surfaces of the spacers and at the same time secure a firm mounting of the electrodes on the spacers. The capacity effects between such projecting portions are a serious deterrent to high grid-plate transconductance at ultra-high frequency.

Another consideration affecting high transconductance is the output capacity between the plate and other electrodes of the device. This capacitance is a function of the surface area o the anode.

The transconductance of the device when used at ultra-high frequencies is also adversely affected when the leads used to connect the electrodes to essential circuit elements are relatively long and thin. Such leads introduce substantial reactance which reduces the transomductance.

It is sometimes desirable to include in a common envelope a dual electrode assembly for use in push-pull amplification applications. A device employing a .dual electrode assembly is characterized by more serious reactance effects and, consequently, a greater sacrifice in transconductance than a device employing one electrode assembly. because of the increased number of elements used.

Accordingly, it is the object of the invention to provide an electron discharge device useful at ultra-high frequencies and characterized by a relatively high grid-plate transconductance.

A further object is to .provide a multi-grid electron discharge device wherein the grids are relatively closely spaced and the control grid is relatively close to the cathode without increasing objectionable reactance of the device.

Another object is to provide a control grid and a screen grid that will be characterized by a relatively small displacement towards adjacent electrodes, when heated, that is insufficient to bridge the space between any one grid and its adjacent electrodes.

A further object is to provide a control grid and a screen grid having side rods displaced from the active portions of the grids and of the cathode for a reduction of the capacity effects between said side rods and the cathode.

Another object is to provide a mount for an actance thereof including leads of relatively large cross section.

Another object is to provide a dual electrode assembly for push-pull operation at ultra-high frequency and in which the grid-plate transconductance is relatively high.

A further object is to provide an electron discharge device having two electrode assemblies serviceable selectively as one or two electrode units and characterized by a relatively high gridplate transconductance at ultra-high frequencies.

The foregoing objects are attained in accordance with the invention by the provision of a control grid and screen grid of novel construction, each including two grid side rods havin transverse grid wires extending to one side of the plane of the rods. The grid wires are formed to have two relatively sharp bends for absorbing expansion of the grid wires when heated in operation. The grid wires are flattened out between the bends referred to and serve as the active portion of the grid. The grids are preferably mounted with the grid side rods spaced farther from the plane of the cathode than the intermediate active portions thereof, to reduce capacity effects between the cathode and the side rods.

One of the grids referred to, serving as the control grid is disposed relatively close to the cathode. The cathode is provided with a relatively large emitting area for producing a copious supply of electrons and having plane surfaces to provide equality in spacing to the grids. Another of the grids serves as a screen grid and is closely spaced with respect to the control grid.

This structure of the grids and their spacings with respect to each other and the cathode contribute to reduction in input capacitance in a device in which they are employed. A further contribution to a reduction of both input and output lead impedances is afforded by the relatively thick leads provided for according to the invention.

A reduction in the output capacitance according to the invention is accomplished by providing an anode having relatively small surface area in combination with beam forming means to assure receipt by the anode of substantially the entire space current.

These features of the invention are particularly advantageous where the device includes a dual electrode assembly, and permits such device to be used selectively as a single assembly device or as a dual assembly tube.

Further objects and advantages of the invention will become apparent as the description continues.

Referring to the drawing for a better understanding of the invention:

Fig. 1 shows a sectional elevation of an acorn type of electron discharge device utilizing my invention;

Fig. 2 is a cross-section along the line 2-2 of Fi l and indicates the structure and relationship of the electrodes with respect to each other;

Fig. 3 is a transverse view partly in section along the line 33 of Fig. 1;

Fig. 4 is a sectional elevation of a miniature type of electron discharge device having a flat stem, that incorporates the invention;

Fig. 5 is a transverse view partly in section along the line 5-5 of Fig. 4; and

Fig. 6 is a perspective view of the shield employed in the device shown in Fig. 4.

Referring more in detail to the drawing, the several figures thereof show electron discharge devices which may either constitute a single or double pentode, the electrodes of each device 4 being constructed and related to each other in such a manner that the device may be utilized in girauits requiring either a single or double pen- The term "pentode is employed in this specification to denote a tube having a cathode, a control grid, a screen grid and a beam forming grid, as shown in Figures 1 to 5, inclusive, of the drawing. In some of its aspects the invention is not limited in usefulness to pentodes only. For example, a tubeemploying a cathode, an anode and two wound grids between the cathode and anode, may with advantage include the features of the invention comprising close spacing between the cathode and control grid and between the two grids. In addition, it is known that certain tetrodes have pentode characteristics and the invention is also useful in these types of tetrodcs.

According to the invention a mount structure is provided that contributes to increased gridplate transconductance in a device in which it is used. This result is accomplished according to one aspect of the invention by the use of a pentode type of electron discharge device, having a cathode of relatively large emitting area, a control grid and screen grid of novel construction, a beam forming electrode, suitable shields for shielding portions of the electrodes projecting beyond the insulating spacers, and leads of relatively large cross section.

The device illustrated in Figures 1, 2 and 3 is an acorn type of electron tube including an envelope l0 closed at one end by a stem 1 l. The stem and envelope are joined in a radial flange I2 through which a plurality of lead-ins [3 to 2i, inclusive, radially extend. Within the envelope I0 is included a dual electrode assembly comprising a common cathode 22, a common suppressor or shielding grid comprising slotted plates 23, 24 connected together by a closed box-type shield 25 disposed above an upper insulatin spacer 2B, and by an open box-type shield 21 disposed below a lower insulating spacer 28. The anodes 29, 30 as well as the control grids 3|, 32 and screen grids 33, 34 may be independently and insulatingly supported within the envelope and connected to separate lead-ins.

. As shown in Fig. 2, a dual assembly electron discharge device according to the invention includes the cathode 22, comprising a sleeve that is relatively flat in cross section and provided with two opposite emitting surfaces of relatively large area. The sleeve is heated indirectly by a heater-35 insulated therefrom. A copious supply of electrons is provided by the large emitting areas of the cathode.

Control grids 3|, 32 of novel construction are positioned relatively close to the emitting surface of the cathode. While the combination of a large area cathode with a closely spaced grid has heretofore resulted in prohibitive input capacitance, this is avoided according to the invention by a novel structure of the control grids 3!, 32 to be more fully described below.

Screen grids 33, 34 are relatively closely spaced with respect to the control grids 31, 32' and are disposed to the sides thereof remote from the cathode 22.

The control grids and screen grids referred to are substantially similar in structure except that the control grids have greater transverse extent. In view of this similarity in structure a description of one of the grids, for example, the control grid 3 I, will be sufiicient, it is believed, for a clear understanding of each of the several grids referred to.

Control grid 3| constitutes substantially onehalf of a tubular grid with certain modifications,

or a conventional "flat grid formed by a stretching and flattening jig or tool (not shown) to suitable flatness, with the unwanted wires of one side subsequently removed. It comprises what may be called a longitudinal half of a tubular grid and is consequently of semi-tubular form. It includes grid side rods 36, 36a and a plurality of transversegrid wires 3|, fixed to the side rods. Intermediate the side rods 36, 36a the grid wires 3| are given two spaced and relatively sharp bends 36, 39. The sharp bends referred to result in the displacement of a portion of the grid wires intermediate the bends fromthe plane of side rods 36, 36a. This intermediate portion of the grid wires is preferably flat with all the strands of the wires lying'in one plane.

A grid of this construction may be made by winding grid wire on two pairs of adjacent grid side rods to form a tubular grid having four side rods. A suitable forming tool (not shown) may be employed for shaping the transverse grid wires on the tubular grid to provide between each pair of said side rods a grid wire formation having the relatively sharp bends and the planar portion referred to above. The grid wire between adjacent side rods may then be cut to provide two identical semi-tubular grid structures.

Where a control grid and a screen grid of this type are utilized in an electron discharge device, the control grid may be formed with its side rods 36, 36a farther spaced from each other than the side rods 31, 31a of the screen grid 33, for a purpose to be described below.

As has been indicated before herein it is desirable for several reasons to have two independent sets of control and screen grids, one set disposed on each side of a common cathode. This is advantageous in that it permits the same device to be used at will as a dual electrode assembly device for push-pull operation or as a single electrode assembly device. It also permits each of the grids to be connected to independent lead-ins which may be associated with different or similar circuit elements for double or single electrode unit operation. The use of independent lead-ins, whether the device is employed in pushpull or other applications is advantageous in that it reduces the length of paths of energy travel and consequently lessens capacity effects and increases the transconductance of the device.

when two pairs of independent control grids and screen grids are included in one device it is desirable that each pair of cooperating grids, such as the control grid 3| and the screen grid 33, have a portion intermediate their side rods that constitutes the only active portions of the grids. To accomplish this end it is necessary that the active portion of the grids be spaced relatively closely for reducing capacity effects. The grid side rods 36, 36a of the control grid and the portions of the control grid between the side rods and the bends 38, 39, should be spaced as far as possible from the side rods 31, 31a of the screen grid and analogous portions of the screen grid 33 to contribute to a further reduction in capacity effects. This desired spacing is accomplished according to the invention by forming each of grids 3|, 33 so that grid side rods 36, 36a. of, the control grid are farther spaced from each other than the side rods 31, 31a. of the screen grid. The grid side rods 36, 36a, 31, 31a, may be disposed in anysuitable array and the invention therefore permits a close spacing between the active portions thereof, and disposes inactive portions thereof in relatively widely spaced locations where their capacity effects are negligible.

To further reduce the capacitance of the device particularly in the output thereof, the anodes 28, 30 are provided with a relatively small surface area and are connected to independent leadins. A suitable shield comprising plates 23, 23 electrically connected together and preferably tied to the cathode 22 is provided for shielding the anode from the inactive portions of the grids and for forming the spaced current into a beam for assuring its travel to the relatively small anodes 26, 36.

The shield 23, 23 preferably extends above the upper mica spacer 26, and may be integral with or electrically connected to the closed box-type shield 26 disposed above this spacer. This boxtype shield effectively, shields the projection tabs 33, of anodes 26, 30 from the input electrodes of the device, as shown in Fig. 1. Another but open shield 21 is provided below the lower spacer 28 as shown in Fig. 3 and is electrically connected to shield 29, 33. It serves to shield the tabs 31, 33 of the anodes 29, 36, from portions of the input electrodes such as the cathode 22 and the side rods of the several grids extending below the lower spacer.

The leads l3 to 2|, inclusive, as shown in Fig.

3 are relatively large in cross section, and the connectors connecting them to electrodes of the device, for example, connector 33, are made of relatively heavy sheet metal of relatively large width. Thiscontributes to a further reduction in the reactance of the device. I

A modification of the invention is shown in Figures 4, 5 and 6. In this modification the invention is embodied in a miniature type of electron discharge device. This device includes a dual electrode assembly having a common cathode 22 and two sets of control grids 31, 32, screen grids 33, 33 and anodes 29, 36. These electrodes are similar in structure and function to those previously referred to in connection with Figures 1 to 3. The electrode assembly presently discussed diflers from that previously described solely in the structure of the shield or suppressor grid which comprises two slotted plates each having legs 5|, 5Ia and 52, 52a and transverse portions 53, 63a and 53b, as shown in Fig. 6. The legs 5|, 51a, 52, 52a are threaded through slots in the upper and lower spacers 26, 28 shown in Fig. 4 and the transverse portions 53, 53a, 53b are positioned above the upper spacer 26 to form a shield between the anode tabs 33, 35 extending above spacer 26, and portions of the input electrodes projecting above this spacer. The legs of the shield extend below the lower spacer 23 and are electrically connected to a lower shield 53 shown in Fig. 4 which may be similar to the lower shield 36 shown in Fig. 3. The shield may be connected electrically to the cathode 22. The shield structure shown in Fig. 6 is advantageous .in that it is easily mounted on the spacers 26,

28 by merely being threaded through slots provided therein and the one threading operation results in a shield for the electrodes between the spacers referred to, as well as a shield for portions of the electrodes projecting above the upper spacer 26.

The leads 55 shown in Fig. 4 are of relatively large cross section and the connectors, not shown, between the leads and their associated electrodes within the device are'made of relatively wide sheet metal to contribute to a reduction in reactance.

It will be noted from the foregoing that an electron discharge device having reduced capacitance and increased grid-plate transconductance is provided that is particularly suited for ultra high frequency operation. A major contribution to good operation of the device is represented by the novel structure of the control and screen grids and the use of two independent sets of such grids. The two independent sets of grids not only serve to reduce capacitance of the device but render the device selectively suitable for push-pull operation or as a single unit electron discharge device by merely changing external circuit elements.

Various modifications may be made in the embodiment described without departing from the invention and it is desired to include such modifications within the spirit and scope of the appended claims.

I claim:

1. An ultra high frequency electron discharge device including a cathode and control and screen grids, said grids having side rod and wire strands afllxed thereto, a portion of said wire strands intermediate said side rods on each.of said grids lying in a common plane, said portion of said wire strands on said grids being in registry with said cathode and relatively closely spaced with respect to each other and said cathode, said side rods being spaced farther from the plane of said cathode than said portion of said grids, a surface of said cathode and said side rods lying in two spaced planes.

2. An ultra high frequency electron discharge device including a cathode, a plurality of grids including a control and a screen grid, side rods for said grids, said grids including planar portions intermediate said side rods, said planar portions being in registry with said cathode and relatively closely spaced with respect to each other and said cathode, the side rods for said grids lying in a common plane, said side rods and said cathode lying in two spaced planes.

3. An ultra high frequency electron discharge device including a cathode and a plurality of grids comprising a, control and screen grid, side rods for said grids, wire strands fixed to said side rods, said strands including planar portions in registry with said cathode and relatively closely spaced with respect to each other and said cathode, said side rods being spaced farther from said cathode than said planar portions, two of said side rods supporting the screen grid, two others of said side rods supporting said control grid, said first mentioned two of said side rods being more closely spaced with respect to each other than the other two of said side rods.

a. An ultra high frequency electron discharge device comprising a cathode, a control grid adjacent said cathode, an anode, and a screen grid between said control grid and anode, said control grid and screen grid including side rods,

.the side rods of said control grid being farther spaced from each other than the side rods of said screen grid, grid wires on said side rods, said grid wires being closer to said cathode than said side rods, said grid wires on one rid being relatively closely spaced with respect to the grid wires on the other grid and having relatively sharp bends therein parallel to said rods, whereby expansions of said grid wires are absorbed by said bends to prevent shorts across the grid wires of the two grids and across the grid wires of the control grid and the cathode, said grid wires including portions intermediate said bends lying in two spaced parallel planes, said portions being in registry with said cathode and said anode.

5. An ultra high frequency electron discharge device having a relatively low input capacitance, comprisin two control grids, two screen grids and two anodes, independent leads-ins for said grids and anodes having relatively large cross section, and a common cathode having rela tively large emitting surface area, said control grids having planar portions closely spaced with respect to opposite sides of said cathode, said screen grids being disposed between said anodes and said control grids and closely spaced with respect to said control grids, side rods for each of said grids lying in planes spaced from the plane of said cathode, the side I'Ods of said control grids being farther spaced from said cathode than the side rods of said screen grids and shielding means between said side rods and said anodes.

6. An ultra high frequency electron discharge device having relatively high grid-plate transconductance, comprising a plurality of electrodes including a cathode of relatively large surface area, a control grid having a plurality of grid wires, a portion of said grid wires lying in a common plane relatively closely spaced with respect to said cathode, a screen grid on the side of said control grid remote from said cathode and including a plurality of grid wires, a portion of said last-mentioned grid wires lying in a common plane parallel to and relatively closely spaced with respect to said first-mentioned plane, said portions of said control grid and screen grid being in registry with an emitting surface of said cathode, an anode of relatively small surface area in registry with said cathode and said portions,'a shield intermediate said anode and said screen grid for concentrating the space current on said anode, said control grid and screen grid having side rods, the side rods of said control grid being farther spaced from said cathode than the side rods of said screen grid, said shield extending intermediate said side rods and said anode, whereby the input and output capacitances of the device are reduced.

7. An ultra high frequency electron discharge device having a relatively high grid-plate transconductance comprising a plurality of electrodes including a control grid, 2. screen grid and a cathode, said cathode having a relatively large planar emitting surface, side rods for said control grid and screen grid, said side rods being parallel to said emittingsurface and disposed one side of said surface and lying in a common plane, said control grid and screen grid each including a plurality of strands of grid wire supported on two of said rods, said strands being disposed to one side of the plane of said two of said rods, a portion of said strands intermediate said rods lying in a common plane parallel to the plane of said emitting surface, other portions of said strands adjacent said rods lying in planes angularly disposed with respect to said emitting surface and extending away from said common plane and the plane of said cathode, whereby bends are provided in said strands for absorbing expansions thereof during operation of the device, said first-named portion of said control grid being relatively closely spaced with respect to said cathode, said other portions of said control grid being relatively distantly spaced from said cathode and fixed to said two of said rods, an anode of relatively small surface area in registry with said emitting surface of said cathode and said first-mentioned portion of said control grid and screen grid, and a shield electrode intermediate said anode and said other portions of said strands of said control grid and screen grid whereby input and output capacitances of said device are reduced.

8. An ultra high freqi'ency electron discharge device having a relatively high grid-plate transconductance comprising a pentode electrode assembly including a cathode having a relatively large fiat emitting surface, a control grid including a plurality of wire strands, two spaced grid side rods for supporting the ends of said strands, said strands including portions intermediate said rods lying in a plane parallel and closely spaced with respect to said emitting surface, the side edges of said portion joining other portions of said strands angularly disposed with respect to the plane of said emitting surface and receding from said plane to absorb expansions of said portion during operation of the device to prevent shorts between said portion and said emitting surface, and a screen grid having side rods and strands of wire fixed at their ends to said rods, the last named side rods lying in the plane of the first named side rods, said strands including a portion lying in a plane parallel to and relatively closely spaced with respect to said I device having a relatively high transconductance first-named portion, said last-named portion terminating in opposite sides formed by relatively sharp bends in said strands extending parallel to said rods for absorbing expansions of said strands during operation to thereby prevent shorts between said control grid and said screen grid.

9. An ultra high frequency electron discharge device having a relatively high transconductance and including a plurality of electrodes comprising a cathode having a relatively large planar emitting surface, a control grid relatively closely spaced with respect to said emitting surface, means for preventing shorts between said control grid and said surface in response to expansion of said grid during operation, said means including relatively sharp bends in said grid in portions thereof out of registry with said emitting surface and extending parallel to said surface, and a screen grid relatively closely spaced with respect to said control grid and disposed on the side of said control grid remote from said emitting surface, said screen grid having relatively sharp bends therein parallel to the firstmentioned bends for absorbin expansions of the screen grid during operation to thereby prevent shorts between the screen grid and the control grid, said control grid and screen grid each having two side rods, the side rods of the control grid being farther spaced from said emitting surface than the side rods of the screen grid.

10. An ultra high frequency electron discharge and including a plurality of electrodes comprising a cathode having a relatively large planar emitting surface, a control grid relatively closely spaced with respect to said emitting surface, means for preventing shorts between said control grid and said surface in response to expansion of said grid during operation, said'means including relatively sharp bends in said grid in portions thereof out of registry with said emitting surface and extending parallel to said surface, and a screen grid relatively closely spaced with respect to said control grid and disposed on the side of said control grid remote from said emitting surface, said screen grid having relatively sharp bends therein parallel to the firstmentioned bends for absorbing expansions of the screening grids during operation to thereby prevent shorts between the screen grid and the control grid, said control grid and screen grid each having two side rods, the side rods of the con trol grid being farther spaced from said emitting surface than the side rods of the screen grid, an anode of relatively small surface area for receiving the space current traversing said screen grid, and means for concentrating said space current in registry with said anode.

11. An ultra high frequency electron discharge device having a relatively high transconductance and including a plurality of electrodes comprising an anode, a cathode having a relatively large p anar emitting surface, a control grid relatively closely spaced with respect to said emitting surface, means for preventing shorts between said control grid and said surface in response to expansion of said grid during operation, said means including relatively sharp bends in saidgrid in portions thereof out of registry with said emitting surface and extending parallel to said surface, and a screen grid relatively closely spaced with respect to said control grid and disposed on the side of said control grid remote from said emitting surface, said screen grid having relatively sharp bends therein parallel to the first-mentioned bends for absorbing expansions of the screen grids during operation to thereby prevent shorts between the screen grid and the control grid, said control grid and screen grid each having two side rods, the side rods of the control grid being farther spaced from said emitting surface than the side rods of the screen grid, parallel insulating spacer plates between which said. electrodes are supported, a portion of said electrodes projectin beyond the outer faces of said plates, and means for shielding the projecting portions of the anode from the projecting portions of the other electrodes.

DON G. BURNSIDE.

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

UNITED STATES PATENTS

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