US2857544A - Electron discharge device anode structure - Google Patents

Description

.Oct. 21, 1958 r J. F. STEPHENS 2,857,544

ELECTRON DISCHARGE DEVICE ANODE STRUCTURE Filed 001:. 21, 1955 L nt E Y S 5 U u U W w 0 0 T 3 D 5V V LO V0 0 AN ER... NA 1 mu T T E i 0 R ES 08 3 ET VO 2T WS NB M 6 0R 0M V H PE CE .0 MU E A 2 v E O 6 H M w l w O .E D ,1 l1 5 J nu l O O O 0 w w M. w 5 l l l 2253.23

INVENTOR JOE F. STEPHEN S United States Patent ELECTRON DISCHARGE DEVICE ANODE STRUCTURE- Joe F. Stephens, Owensboro, Ky., assignor to General Electric Company, a corporation of New York Application October 21, 1955, Serial No. 541,967 3 Claims. (31. 313-299 My invention relates to electron discharge devices and more particularly to beam power tubes and strueturesfor minimizing spurious oscillations within said tubes.

Those electron discharge devices including a cathode, an anode, a control grid, a screen grid and having shaped electrodes for the purpose of concentrating and confining the electrons so that the electrons emerge as defined beams are known as beam power tubes. In addition the grids of said tubes have parallel spacings to further concentrate the electrons in beams. The electron density effects the space charge region existing between the screen grid and the anode to produce a negative voltage gradient near the anode which acts as a virtual cathode and eliminates the necessity of a suppressor grid in reducing secondary emission effects. Beam power tubes have the advantages of high power output, high power sensitivity, high efficiency and are consequently extensively used. However, aproblem associated with the use of beam power tubes is that of spurious oscillations. For example, when using beam power tubes in the horizontal deflection circuitry of television receivers, spurious oscillations emanating from the beam power tubes are radiated, picked up by the signal circuit of the receiver, amplified as picture information and appear as cyclic interference on one side of the picture tube raster as a vertical band or bands, either curved or straight, continuous or broken, depending upon the strength of the oscillations.

Accordingly, it is an object of the present invention to provide improved electron discharge devices of the beam power type in which spurious oscillations are prevented or greatly reduced.

Another object of the invention is to provide an improved anode structure for beam power tubes.

Yet another object is to devise a novel method for suppressing spurious oscillations in a cathode ray tube deflection system.

Further objects and advantages will become apparent from the following description and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of the specification.

In carrying out the objects of the invention, I provide a novel anode structure for a beam power tube for the purposes of suppressing spurious oscillations in said tube.

For a detailed explanation of the invention, reference is made to the accompanying drawings in which:

Figure 1 is an isometric view, partly in cross section, of a beam power tube showing an anode made according to my invention.

Figure 2 is a cross sectional view taken along the line 2--2 of Figure 1.

Figure 3 is a graph of tube current versus voltage characteristic curves showing the comparison and advantages of beam power tubes incorporating my invention.

In Figure 1, there is shown a beam power tube envelope 11, having a cap connection 12, and an electrode assembly 13 within said envelope 11 including an anode "ice 16 rectangular in cross section mounted between two mica plates 14 and 15. Anode 16 surrounds the other elements of electrode assembly 13 and is connected to the outside power source (not shown) through the lead 17 and cap 12. Barium getter assembly 18 is shown mounted above the mica plate 14. The various pin-wire connections to the tube may be of conventional design and are not, per se, a part of this invention and therefore are notshown and will not be further described.

Figure 2 is a cross sectional top view taken along line 2-2 of Figure 1 and better shows my invention. In Figure 2, electrode assembly 13 consists of cathode 21, control grid 22, screen grid 23, and beam confining plates 24 disposed so as to confine oppositely directed electron beams 29 and 29' therebetween.

In accordance with my invention, the anode 16 is formed with similarly shaped embossments 25 and 26 centrally positioned on opposite sides of the rectangular anode 16 and projecting inwardly toward the space- charge regions 20 and 20 where the anode intercepts the electron beams 29 and 29. Embossments 25 and 26 extend along the length of the anode 16, and have a double humped or double U-shaped contour. Anode 16 may be formed of two cup-shaped similar pieces 27 and 28 which are joined at their open ends to form a complete closure. Pieces 27 and 28 may include fins 19 and 19' which extend in opposed directions and perpendicularly to the sides of the rectangular anode; said .fins 19 and 19' are aflixed to each other and serve as a means of heat dissipation.

It is believed that the spurious oscillations in the beam power tube which cause the picture interference are the result of current discontinuities within the tube and further that the current discontinuities are caused by a shift of the virtual cathode during the portion of the operating cycle during which the plate potential islow. This belief appears sound since the eifect is most pronounced when the beam-power tube is employed as a deflection tube and is driven at low values of plate voltage; the current disc'ontinuities of the offending tube appear to be traceable to the portion of the plate characteristic curve (I vs. E

known as the knee, see Figure 3. The frequency of the oscillations is dependent upon the dimensions and po-;

tentials of the tube.

In the graph of Figure 3 curves of the tube current versus voltage characteristics are plotted to show the comparison and advantages obtained when employing beam power tubes incorporating the anode of my invention as in contrast with conventional beam power tubes. In the graph the axis of abscissas represent E anode voltage in volts, and the axis of ordinates represent I plate current in milliamperes; the curves are plotted for constant values of E,,, the grid bias voltage.

Conventional beam power tubes are characterized by having abrupt sharp knees and negative transconductance characteristics, that is, for a constant low value of plate voltage higher values of plate current result when using higher negative values of grid bias. The negative transconductance characteristic region is evident between point A and point .B of the conventional tube characteristic curves, Figure 3. Therefore, if the tube is to be driven into or below the knee the immediate task is to round the sharp knee and to eliminate the negative transconductance characteristics in a manner which will not be deleterious to the aforementioned tube characteristics and quality characteristics which make the tube highly desirable commercially.

I have found that the shape of the knee and the slope of the curve is a function of the electron focusing between the screen or number two grid and the plate. An anode located at too great a distance from the screen adversely affects the power output, sensitivity, and efiiciency of the tube while an anode located too near the screen causes undesired secondary emission.

The anode 16 of my invention is formed with embossments or projectionsZS and 26-for thepurposes oftvary ingthe focusing of" the electron beams and 29 witli out changing the secondary emission suppressing function of' space-charge regions 20' and, ZW'Iocatedbetweenv the anode 16 and'the screen grid23} Contiguous points; on embossments 2'5 and 26 are atvariably spaceddist'ance.

characteristic curves below the knee, is actually increased and indicates that thenegative transconductance operating region is elirnihatedi Figure 3 clearly shows the marked improvement obtained using. a' beam power tube incorporating my invention;

As has been previously stated, when a beam power tubeof thetype heretofore known is used in the horizontal deflection system of a television receiver, the tube will cause transient or spurious oscillations which will result in vertical lines on the'picture tube of a television receiver: Inabeam power tube incorporating my invention by virtue of the embossments 25 and 26'which projectinwardly toward the space charge region20, spurious oscillations-are eliminated or sogreatly reduced that no interfering-lines are apparent on a television receiver. Beam-power tubes-incorporating my invention may also be advantageously used to reduce high-frequency interference/in the o'utput-of aradio receiver;

While specific examples liave beengiven in describing details of this-:invention, it Will be understood'that they have been given merelyby way of illustration and that the invention-is notlimited thereto: Further, while I have-suggested employing the beam power incorporating my invention in a deflection circuit of a' television receiver or in the'output stages of a radioreceiver it'will be understood that the use ofsaid" tube is not limited theretoand that other uses will be apparent to those skilled in the art;

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A beam power tube comprising an anode, a cathode, a screen grid, beam-confining electrodes disposed between said screen grid and said anode, said anode having curved surface portions extending toward the space bounded by said anode, said screen grid, and said beam forming electrodes; and said curved surface portions'having a double U-shaped contour.

2. A beam power tube comprising an anode, a cathode, a screen grid, beam-confining electrodes, saidanode comprising two cup-shaped members joined to" defihejunc- I tions-at-the. open ends thereof and havinginwardly-projecting embossments adjacent said junctions and eXtend-' ing toward the space bounded by said anode, said screen grid and said beam forming electrodes, and said embossments having a double U-shaped contour.

3. In a beam power. tube comprising electron beam producingmeans, a control. grid, a screen: grid, beam confiningelectrodes, and an anode said beam confining electrodes being elongated and defining longitudinally elongated oppositely directed beams, said anode comprisinganelongated box-like member surrounding the other i of said electrode elements and including oppositely dis-v posed portions each intercepting only' one of said beams, and each of said oppositely disposed portions of said anode including, a pair of parallel; longitudinally, inwardly extending' curved' surface poftionsdisposed in the intermediate areaof each of said beam intercepting portions of said anode, each pair of saidcu'rved surface portions havingra double U-shaped' contour and effecting substantiallyvariable interception of the electrons of said beam, whereby undesired oscillations" in said tube are sup pressed.

References Cited in the=filei of this patent UNITED STATES PATENTS France May 9, 1949

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