US2724069A - Thermionic valves - Google Patents

Description

Nov. 15, 1955 A. J. YOUNG ET AL 2,724,069

THERMIONIC VALVES Filed March 23, 1951 4 Sheets-Sheet 1 Nov. 15, 1955 A. J. YOUNG ET AL THERMIONIC VALVES 4 Sheets-Sheet 5 Filed March 23 1951 Nov. 15, 1955 J, You ETAL 2,724,069

THERMIONIC VALVES Filed March 23, 1951 4 Sheets-Sheet 4 m m-& MW M mmw i Awwwlggt FIGB.

United StatcsPatent Ofiice 2,724,069 Patented Nov. 15, 1955 1 2,724,069 THERMIONIC VALVES Arthur James Young, Danbury, and David Carlton Dehlsen, Chelrnsford, England, assignors to English Electric Valve Company Limited, London, England, a company of Great Britain Application March 23, 1951, Serial No. 217,109 Claims priority, application Great Britain March 3%, 1950 6 Claims. (Cl. 313-293) This invention relates to thermionic valves and has for its object to provide improved thermionic valves suitable for use for so-called power amplification.

Although the invention is not exclusively limited to triodes it is mainly intended for valves of the type in which there is only one control grid electrode between the cathode and the anode. However, as will be apparent later herein, the invention is also applicable to valves having more than one grid between cathode and anode.

The invention is illustrated in and explained in connection with the accompanying drawings in which Figs. 1, 3, 5, 8 and 9 are explanatory graphical and schematic figures, Fig. 2 illustrates a typical known valve and Figs. 4, 6 and 7 illustrate the present invention.

When a triode is employed as a power amplifier the maximum power output practically obtainable is limited by the maximum permissible anode voltage and the maximum permissible peak anode current. Referring to Fig. 1 of curves connecting anode current Ia (ordinates) with anode voltage Ea (abscissae) are drawn in the conventional way for a triode of normal construction the curve DL for the condition in which anode voltage and control grid voltage are equal is a substantially straight line inclined only a small amount to the ordinate line and sloping up from the origin. This line is usually called the diode line for a reason which is obvious. Also the so-called load line LL is a substantially straight line sloping downwards from a point in the ordinate line and terminating in a point in the abscissa line, the positions of these points depending, of course, upon the valve construction. The load line intersects the diode line and in a normal amplifying valve the point of intersection is the point P at which the grid current is greatest and also the point at which the ratio of anode current to grid current is least. In practice, with usual known valve structures, the valve may be driven along the load line to this point of intersection but if the grid becomes more positive to the cathode than the anode the grid current becomes execssive. High grid current is, of course, a serious disadvantage for it imposes load upon the stage driving the valve, causes heat loss in the grid, and takes up part of the total cathode emission current. It is therefore very desirable to reduce grid current as far as possible and indeed the utility or value of a power amplifier valve may be and commonly is expressed as the ratio of anode current to grid voltage at maximum operating anode current i. e. at the point P in Fig. 1. This ratio is commonly of the order of from 2 to 3 in present known valves of usual construction. The. present invention seeks to provide improved valves in which, this ratio is of substantially higher value and by means of the present invention a ratio of fouror even more can be obtained.

According to this invention a thermionic valve comprising a cathode in the form of a plurality of Wires, strips or the like elements, an anode and at least one control grid which is alsoin the form of a plurality of wires, strips or the like elements, interposed between the cathode and the anode'is characterized by the provision, on the side of the cathode remote from the anode, of an additional grid composed of wires, strips or the like elements and adapted to concentrate or direct the electron streams from the cathode elements towards the anode through spaces between the elements of the conrol grid whereby portions of the electron stream which would otherwise reach the control grid elements fall upon the anode.

Preferably the additional grid is so positioned 'as to be adapted to produce the required action when at cathode potential. This enables the additional grid to be directly connected to the cathode, if required, in the structure of the valve itself.

The anode, control grid or grids, cathode and additional grid may all be of concentric cylindrical shapes one within the other, though, as will be seen later, this is not a necessary feature of construction.

The operation of a valve in accordance with this invention will best be understood by considering first what takes place in a known triode of the kind in which the anode, control grid and cathode are of concentric cylindrical shape the control grid and cathode being in the form of cages of wires with the wires of the cathode radially behind the spaces between the wires of the control grid. Thus to take a typical example of this known type of construction and illustrated in Fig. 2 the cathode and the control grid may consist each of a cage of wires all running parallel to the axis of the concentrically'surrounding anode A, the control grid having twice as many wires CGW as the cathode and each cathode wire C W being radially behind the. mid-point of the space between a different pair of, wires CGW of the control grid. With such a valve, if the anode -and control grid are brought to the same potential-that is to say, if the valve is in the diode condition-thcn, considering any one of the cathode wires and the four nearest control grid wires (two to each side of the said cathode wire) it will be seen that the total cathode current may be regarded as made up of seven lobes or streams as shown in Fig. 3. Of these seven lobes three extend from the cathode Wire to the anode through the three spaces which are between the four control grid wires. In Fig. 3 these three lobes are indicated by a single hatched area marked L3. The other four lobes do notterminate in the anode, but are concentrated on the control grid wires themselves. Two of these four lobes, indicated in Fig. 3 by the hatched areas L2 are small and are in the spaces between the three lobes comprised in the area L3 but the other two are large. These two large lobes are indicated by the hatched areas L1 in Fig. 3 and terminate in the two outermost of the four grid wires CGW considered and extend outwardly of and curve to some extent rearwardly of, the two outermost of the three lobes comprised in the area L3. The four lobes L1 and L2 of course contribute to grid current and the present'invention provides what is in eflfect a focussing electrode system which is in the form of a cage of wires behind the cathode wires (that is to say on the side thereof remote from the anode) and which operates to eliminate or at any rate substantially reduce the two large outer lobes L1. This focussing electrode system or grid may consist of a cage of wires concentrically within the cathode cage and with its individual wires behindthe spaces between the individual Wires of the cathode cage.

By suitably positioning the 'focussing grid provided by this invention and suitably choosing thedimensions of its wires it is possible in accordance with known principles to achieve the required action when holding said grid at cathode potential and this is the preferred construction. It is not, however, an essential feature for the desired result may be obtained by putting a suitably designed focussing grid in almost any desired position (within a wide range) behind the cathode, insulating it and, in use applying thereto the appropriate operating or focussing potential. H i

Fig. 4 shows diagrammatically one form of valve in accordance with this invention. Here there are four concentric cylindrically shaped electrodes of which the outermost A is the anode cylinder, the next (proceeding inwardly) electrode is a cage of wires CGW constituting the control grid, the next electrode is a cage of wires CW constituting the cathode and the innermost electrode is a cage of wires FGW constituting the focussing grid provided by this invention. There is the same number of wires FGW-all running parallel or approximately parallel to the axis -in the focussing grid as there is in the cathode, the wires of the focussing grid being radially behind the mid-points of the adjacent spaces between cathode wires CW. The control grid contains twice the number of wires FGW as the cathode, the wires of the cathode being radially behind the mid-points of the alternate spaces between the wires of the control grid. The focussing grid wires, like the cathode wires, are evenly spaced round their respective cylinders, but the spaces between adjacent control grid wires are alternately long and short, the cathode wires being radially behind the middles of the shorter spaces and the focussing grid wires being radially behind the middles of the longer spaces.

. Fig. 5 shows in manner similar to that adopted for Fig. 3 the improved results obtained, or approximately obtained by this invention. In Fig. 5 the same references are used as in the other figures and it will be observed that, as compared to Fig. 3, the lobes L1 have disappeared while the changed shape of the area L3 will be noticed.

Figs. 6 and 7 illustrate an actual practical embodiment of the invention, in mutually perpendicular views, these figures showing only those parts necessary to an understanding of the invention. In these figures the same references'are used as before FGW being the focussing grid wires, CW the cathode wires, CGW the control grid wiresand A the anode (not shown in Fig. 6)

The great practical improvement obtainable by the invention will be seen from a comparison of Fig. 8 and 9 which are to the same scales and in each of which grid current (curve 1) anode current (curve 2) and total current i. e. anode current-l-grid current (curve 3) is plotted against control grid and anode potential, the control grid and anode being strapped together. Fig. 8 shows the actual results obtained from a valve as shown in Figs. 6 and 7 while Fig. 9 is for a known valve which is similar except for the omission of the focussing grid FGW provided by this invention. valve (see Fig. 9) at 1000 v. applied voltage the ratio of anode current to control grid current is only 2.14 whereas, for the same potential on the improved valve (see Fig. 8) the ratio is increased to 3.52.

The invention is not limited to the cylindrical type of construction above described but may be embodied in the flat or flattened elliptical type of construction the grids (focussing and control), the cathode, and the anode all being in parallel planes.

We claim:

1. A thermionic valve comprising a cathode in the' form of a plurality of conductor elements, an anode and at least one control grid which is also in the form of a plurality of conductor elements interposed between the said cathode and the said anode, said control grid extending across the electron stream path from cathode to anode to control the electron flow from cathode to anode through the inter-conductor spaces of said con trol grid and wherein there is provided, an additional grid composed of conductor elements, each said conductor element situated opposite the space between two adjacent cathodeconductor elements and, said additional grid being situated on the side of said cathode remote from said anode and adapted when maintained at a pre-determined potential to concentrate the electron streams emitted from said cathode conductor elements on the It will be seen that, for the known side remote from said anode towards said anode through the spaces between the control grid elements thereby to divert electrons from said control grid elements to said anode.

2. A thermionic valve comprising a cathode in the form of a plurality of conductor elements, an anode and at least one control grid which is also in the form of a plurality of conductor elements interposed between the said cathode and the said anode, said control grid extending across the electron stream pathfrom cathode to anode to control the electron flow from cathode to anode through the inter-conductor spaces of saidcontrol grid and wherein there is provided, an additional grid composed of conductor elements, each conductor element situated opposite the space between two adjacent cathode conductor elements and said additional grid being situated on the side of said cathode remote from said anode and adapted when maintained at substantially cathode potential to concentrate the electron streams emitted from said cathode conductor elements on the side remote from said anode towards said anode through the spaces between the control grid elements thereby to divert electrons from said control grid elements to said anode.

3. A thermionic valve as set forth in claim 1 wherein the anode is formed in a cylinder and wherein the conductor elements forming said grids and the cathode are arranged in concentric cylindrical shapes one within the other and within said anode.

4. A thermionic valve as set forth in claim 2 wherein the anode is formed in a cylinder and wherein the conductor elements forming said grids and the cathode'are arranged in concentric cylindrical shapes one within the other and within said anode.

5. A thermionic valve as set forth in claim 1 wherein the anode is cylindrical and wherein the conductor elements forming the grids surround the cathode conductor elements, said cathode conductor elements being disposed in cylindrical cages, all said electrodes being disposed concentrically within one another, the additional grid conductor elements being equally spaced angularly and each radially opposite the mid-point between adjacent cathode conductor elements which are also equally spaced angularly, the control grid conductor elements being in similarly and closely spaced pairs, each cathode conductor element being radially opposite the mid-point between the conductor elements of a closely spaced pair of control grid conductor elements 6. A thermionic valve as set forth in claim 2 wherein the anode is cylindrical and wherein the conductor elements forming the grids surround the cathode conductor elements, said cathode conductor elements. being disposed in cylindrical cages, all said electrodes being disposed concentrically within one another, the additional grid conductor elements being equally spaced angularly and each radially opposite the mid-point between adjacent cathode conductor elements which are also equally spaced angularly, the control grid conductor elements being in similarly and closely spaced pairs, each cathode conductor element being radially opposite the mid-point between the conductor elements of a closely spaced pair of control grid conductor elements.

References Cited in the file of this patent UNITED STATES PATENTS 1,886,264 Pohlhausen Nov. 1, 1932 2,096,459 Kassner Oct. 19, 1937 2,105,924 Mendenhall Jan. 18, 1938 2,204,306 Harris June 11, 1940 2,224,649 Harris Dec. 10, 1940 2,419,485 Desch et al. Apr. 22, 1947 2,459,792 Chevigny Jan. 25,1949 2,500,574 Rudenberg Mar. 14, 1950 2,512,858 Hegbar June 27, 1950 2,512,859 Smith June 27, 1950

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