US2459072A - Beam power tube - Google Patents

Description

Jan. l1, 1949.

D. G. HAINES BEAM POWER TUBE Filed Jan, 8. 1946 /QTTO/P/VE Y Patented Jan. 11, 1949 BEAM POWER TUBE Donald G. Haines, Elmhurst, Ill., assignor to National Union Radio Cor poration, Newark, N. J.,

a corporation of Delaware v Application January 8, 1946, Serial No. 639,848 3 Claims.4 (Cl. 25u-27.5)

This invention relates to electron discharge devices, and more particularly to electron tubes of the so-called beam power type.

A principal object of the invention is to provide a beam power tube having a plurality of separate emitting cathodes with a special construction of beam forming electrode for improving the operating characteristics of the tube.

Another object is to provide a duplex cathode beam power tube having an improved beam forming electrode construction which acts to confine with greater uniformity the secondary electron beams from the plate or output electrode.

A feature of the invention relates to a novel beam forming electrode for electron tubes of the screen grid type whereby the screen grid potential is rendered substantially independent of secondary emission from the plate.

Another feature relates to a beam power tube having a series of parallel linearly extending cathodes with a common control grid, a common shield grid, and a common beam forming electrode, the beam forming electrode being constructed so that the l-ow or zero potential zone between the screen grid and plate is maintained uniform without substantially affecting the mutual conductance of the tube.

A still further feature relates to the novel organization, arrangement, .and relative location of parts which provide an improved beam type tube capable of handling relatively large power outputs with a, minimum of distortion,

Fig. 1 is a schematic plan View of a tube embodying the invention.

Fig. 2 is a vertical sectional view of a tube according to Fig. 1.

Fig. 3 is a modification of Fig. 1.

Referring to Fig, 1, there is shown in schematic form an evacuated and enclosing envelope I, within which are mounted two elongated electron emitting cathodes 2, 3, each preferably in the form of a flattened metal sleeve whose external peripheral surface is coated with electron emissive material. These cathodes when in use are raised to electron emitting temperature by any well-known heating means (not shown). Preferably the cathode sleeves have opposite flat and substantially parallel faces 4, 5, and 6, 1. Surrounding both cathodes is a common foraminous control grid 8 which may be in the form of a ne wirel helically wound around the usual metal uprights or side rods 9, I0, to which the individual grid turns are fastened. These individual grid turns are usually referred to as grid laterals. Likewise surrounding the cathodes, is

e a common screen grid I I, which may be of a construction similar to the grid 8 and having side rods I2, I3. Preferably, and as is usual in beam power tubes, the grid laterals of screen grid I I are aligned with the corresponding grid laterals of control grid 8 so as to form the electrons from the respective cathodes into a series of parallel layers extending towards the common plate or outputA anode I4. Anode I4 may be supported on suitable metal uprights l5 and I6.

In order to` achieve `the desired beam characteristics', preferably the grids 8 and Il should be in the form of flattenedA helices so that the grid rlaterals lie in respective planes which are substantially parallel to the at faces of the cathodes. In order that the tube may have the desired mutual conductance characteristics, it is important that the space between the screen grid II and the'plate or anode I4 be as free from obstruction as possible. At the same time, in order to control any undesired secondary electron emission from the surface of the plate I4, it is important that a uniformly low or even zero potential zone be established at the appropriate location between the screen grid and the plate. This is particularlytrue where the beams from the cathodes are to be confined to certain restricted areas ofA the plate. Accordingly, there is provided a beam confining or forming electrode system comprising two sections I 'I, I8, each of which is suitably supported on its respective metal upright or side rods I9, 20. These beam forming electrodes may be of any suitable crosssectional shape, and each has fins 2 I-22, 23-24, extending partially into the space between screen grid II and plate I4 so as to provide the necessary 10W potential Zone at the desired region therebetween. i

With the construction as described, the side rods 9, II), I2, I3, are mounted in a common plane so that there is an electron shadow in the vicinity of these siderods. However, when the beam plates I1, I8, are connected to ground cr some other suitable low base potential, they provide a shield against the return of secondary electrons from the plate to the screen grid I I or to the control grid 8. At the same time, these beam plates act to conne the desired electron beams from the cathodes to the desired restricted areas of the plate I4.V In other words, by suitable shaping of the beam plates, the primary electron beams are shaped as indicated by the dotted outlines in Fig. 1, and at the same time the space lying outside the boundaries of` these conned beams are protectedagainst returning secondary 3 electrons to the shield grid or control grid. However, since two separate cathodes are employed, it is not entirely feasible to make sure that the respective beams therefrom overlap suciently to protect the entire active space between the screen grid and the plate against returning secondary electrons. Thisunprotected spacesis indicated schematicallyrin the drawing bythe dotdash outline. In accordance with the invention, there are provided additional rods or metal strips 25, 26, which extend parallel to the length of the cathodes and each of these strips or rodsis .preferably located in substantially the same vrplane as the corresponding fins 2l-22, 223-224, .and are electrically connected thereto by suitable metal strips or the like. With this arrangement, it is possible thereioreftohave eachfcathode produce its individual coniined beam which is acted upon in common by the respective common grids 8 and Il, and these individual beams reach the plate t4 without any substantial Voverlap. `Howeverjthegpresence of the'inembers'25 VandZ- introduces in the unprotected space above- Vmentioned-a suitable Apotential `so that there is provided a `substantiallyuniform zone extending transversely to the electron beams, whichzone is of suiciently lowpotential gradient tofprevent return of substantially Aall secondary electrons from; the plate Id lto anysection of the grid ll or the grid 8. It will be understood of coursethat whenthe tube is in use, Athe screen-grid Il' is operated at a suiciently high positive potential with respect to the ycathode so that this high "potential does not have any eiect beyond the plane defined by the ns 2l-22 and 23-24.

With the Yforegoing described' arrangement the control of the primary electron'beams emanating from the respective cathodes is materially increased, and results in higher `plate impedance and a higher amplification factor. One possible explanation for this is that the effectiveplate `area or zones 27, 28, 29, 3S, on whichA the'primary electrons impinge are not aiected by the presence of the additional rods or-strips 25, 26. lConsequently, these rods or strips may be made 'so thin, considered transversely to the electron beam, that the mutual conductance of the tubeis not appreciably `reduced thereby. On the other hand ythe relatively high positive potential of the plate .26. Therefore, `the plate impedance-of the'tube is increased since the 'distance from "each 'cathode o.; 'to the equivalent triode plate is increased, land Athe,.amplification factor is increased because the equivalent triode is also further removed-from the control grid 'Referring to Fig. 2, there is shown in vertical 60 sectional view a typical construction of electrode mount embodying the principles explained in connection with Fig. 1. The parts of Fig. 2 which correspond structurally and functionally to those of Fig. 1 are designated by the `same. numerals. n Fig. 2, the electrodes are n'supported Ifrom-a common glass header or base 3l which vis-sealed into the bottom of the bulb l but `in the usual manner. Sealed through the header-3i are suitable contact prongs and lead-in members'32-39 llto `which:areiastened as `by-.welding the respec- Vnected by a short metal strap'to the lead-in 34,

'which may also be connectedrto"therbeam'forming electrode system. As shown in Fig. 2, the beam forming electrode system is in the form of a rectangular metal box having rectangular windows in its sides facing the flat surfaces of the 5 cathodes, these Windows being sufficiently large so that the side ns 2l-22, 23-2l5, extend inwardly .towards the longitudinal axis of the "mount, a .distance slightly beyond the ends of the screen grid Il. The horizontal upper mar- .lo gins 40 and the corresponding horizontal lower `margins 4I of each window therefore constitute :inzeiect braces between the two beam forming sections l'l and I8. This type of beam forming platemay therefore be readily stamped out of a mffsingle Ysheet of strip metal and the necessary rigidity and fixed dimensions of the windows are thereby assured. '.The members 25 and 25 above described might then be readily welded at their opposite ends to the horizontal straps 40 and 4I of each window, and these members 25 and '25 in `accordance 'with the inventionV are located mid-waybetweenthe cathodes 2 ari-d3.

While there has been* described a duplex lcath- `ode beam power tube, it will 'be understood that 35 'the-invention' isnot limited to suchA a tube,'com

"prising `only 'two separate cathodes and a corresponding 'singlexpair of members v25, 25. As shown in Fig. Sythe same'principle may be embodied in a larger 'output tube by employing more than ntwo separate cathodes. Thus, as shown 1n this figure, the' tube'has a series of four electron-emitting . cathodes 42, 43, 44, $5, and located .mid-way 'between 'each adjacent pair of cathodes are'located a corresponding pair of space 3;,.shie'1dingro'ds or strips'46-ll, ll8-9f50-5l, corresponding to .the members .25 and 26 of Fig. l. "In this embodiment-fthe remaining parts of the electrode .system Y which correspond` structuruall'yland.functionally to those of Fig. l and.2, bear 4U .the same. designation numerals.

`While certain particular embodiments have been described herein, various changes and modi- ,cations-.maybe made therein, without departing i :fromtthe spiritaandrscope'of the invention. l V`What is claimed is:

l. An amplifier tubeof the beam power type Uconfiprfising "a pair of substantially parallel and :spaced-Y linearY cathodes; a control Vgrid .surroundo =ing said cathodesa shield .grid Asurrounding'isaid 4controlwgridganv output anode for said `cathodes, a pair of beam=formingfelements mounted {adjacent `.the end sections Yoisaid grids, and a conductive member mounted inr said. region and con- -inectedto zsaidaelements to 'provide a fl'etarding potential gradient in said region with'i'espectto electrons tending .to movefrom the anodev toward fthe control fgrid, said "beam-forming elements cooperating with said cathodes to'forin the elec- Y`tron .streams tinto respective rand substantially :non-.overlappingiibeams diverging towards said anode :andwith a .region between said beams havingy low electron density.

:linnn electron discharge tube of the beam :power '.typecomprising a pair of substantially `linearand f parallel Lspaced l cathodes, a `control gr-idsurrounding said cathodes, a shield grid surrounding the control grid, an output anode surrounding-the shi-eid grid, means surrounding-the shield -gri'd "and 'having end Aportions which cooperate with said cathodes to form the electrons finto separater and substantially non-overlapping beams, said means having `Loppositely disposed v`windows facing'the'cat'hodes and each kwindow Lhaving a" transverse 'metal strip electrically -connected thereto and located midway between said cathodes.

3. An amplier tube of the beam power type, comprising, a pair ofsubstantially palallelrand spaced linear cathodes, a controlgrid surrounding said cathodes, a shield `grid ,snrxjonnding said control grid, an voutput VUanqdesurrounding said shield grid, a box-likelmetal member having two of its opposite wallsfacing said cathodes and each provided with a respective window for the passage of electrons from said cathodes to said anode, the Walls of said box-like member constituting a pair of electron beam-forming' plates, and a narrow metal strip extending acrossv each of said windows parallel to said cathodes and located symmetrically with respect to'said cathodes, said beam-forming plates co-aetingY with said cathodes to form the electrons from' said eathodes into respective and substantially non-overlapping beams with a region between the beams of relatively low electron density wherein said narrow metal strips are located, said strips serving to provide a retarding potential gradient in said region with respect to electrons tending to move from the anode toward the con- Great Britain Aug. 30, 1937

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