US2005257A - Vacuum tube grid - Google Patents

Description

June 1935. w. w. EITEL Er). 2,005,257

VACUUM TUBE GRID Filed April 26, 1933 2 Sheets-Sheet} INVENTORS, WILL/AM W. E/TEL a JAcvr MQC'ULLOUGHI BY i ATTORNEY I June 18, 1935'. w. w. ElTEL El AL VACUUM TUBE GRID 2 Sheets-Sheet 2 Filed April 26, 1933 I INVENTORS, WILL/AIM W. E7721 8 JACK McCULLCJl/GH.

/;f ATTORNEY Patented June 18, 1935 VACUUM TUBE GRID I William w. and

Bruno, Calif assignors to Heintz Ltd, San Francisco,

Nevada Application April 26,

2 Claims. (o1,- est-+215) Our-invention relates to vacuum tube grids, and more particularly to grids of the heavy duty type to. be used in high power radio transmitting tubes or power oscillation generators and amplifiers.

Among the objects'of our invention are: To provide a, grid, suitable tor high power vacuum tubes; to provide a gridwhich will not'change its;,control characteristics under load; to provide a grid in whichthe individual control elements remain parallel under varying temperatures; toprovide agrid having a'constant' control characteristic particularly adapted to a vac uum tube. oscillation generator or amplifier op-' cratingv at, high; frequencies; and to provide a simple means and method of preventing physi-' cal expansion of grid control elements from changing the control characteristic ofa vacuum tube.

Other objects of our invention will be apparent or will be specifically pointed'outin the description forming a part'ofthis specification, but we do not limit ourselves to the embodiment of our invention herein described, as various forms may be adopted within the scope of the claims. l

Referring to the drawings:

. Figure 1 is a view in elevation of avacuum tube embodying our invention, theenvelope and the'anode being cut away. to disclose the elements. q

Figure 2 is a sectional view of the tube shown in Figure 1, taken at a plane of section indicated by the line 2-1 in Figure 1. 4

Figure 3 is a view partly in elevation and partly in section taken along the line 3-3 in Fig-' ure 2.

In vacuum tubes of high power outputpused,

as oscillation generators or amplifiers or for like purposes, it is usually necessary to form the grid control wires of metal having a relatively large section, due to the amount of heat generated in operation. The metals used for such control wires almost always have considerable heated, and we have found that when such wires are assembled parallel to each other, asisthe usual custom, and fixed at both ends, that expansion due to the heat of operation will cause a departure from parallelism. This departure causes a change in the control characteristic of the tube, which while producing variation at the higher wave lengths, will create such an alteration of the tube characteristics only a small amount of output and Jack McCullough, San

. &.'Kaufman, Oalifl, fa corporation of 1933, serial no. 668,073

at the low and extremelow frequencies as to render the tube useless for such purposes. I Furthermore, when a tube having @fixed, ex pansible control rodsis used, for example, as a modulated oscillator, or. as an amplifier of high frequencies, modulated, in particular, with. an audio frequency, .the power output and consequent heating of the grid elements is constantly changing, and thevarying physical displacemerits of. the control rods laterally, awayfrom parallelism, introduce a definiteand continuous wave form distortion into the output.

Broadly speaking, forming a grid having a plurality of spaced parallel control elements positioned inv the. electron stream and free to expand longitudinally; A pair' of positioning members are preferably provided to space the ends of the rods, these members being ,fastenedtogether by support elements preferablyasimilar in size and spacing to the control elements. It is desirable to locate the positioning ,membersand the support elements out of the electron stream in a location of low and relativelysteady heat, and to fasten one end of the spaced parallel control elements alternately to each positioning member, allowing the other end to be free as to longitudinal extension, but retaining said end in spaced relation to the other control elements to maintain the elements parallel and free from buckle during-expansion.

Referringto the drawings, which illustrate a preferred embodiment of our invention as applied -,to a-high power vacuum tube oscillation generatorand "amplifier, a vitreous'envelopel is provided at one end with a reentrant stem 2' through which'are sealed cathode leads ,4. An M-type filamentary cathode 5 is mounted on these leads, the two upper bights of the cathode being supported by spring hooks 6 carried bya spring frame! mounted on, a dummy stem 8 which is sealed in the. opposite end of the em; velope. The lower bight of the filament/is posisupported by a pair of anode struts H sealed intothe sideof the envelope, and connected to flanges 12 on- The anode struts pass through the envelope wall and are connected to anode caps l5 mounted-on anode projections l6.

current, supply.

Interposed between the anode and the cathode, is a composite grid structure comprising a pair I of spacing members I! having a series of equally tioned by a cathodelhook 9 sealed into the stem. v An anode '|fl' Sll11'OllI1dS the cathode,:and is the anode by means of a yoke l4,

These caps serve as the exterior contacts for connection to the anode our invention. comprises rod is welded, the opposite grid cage spaced apertures I9 therein, through which the various grid elements may pass to form a cylindrical grid cage. These elements, particularly in tubes of high power, are preferably stiff rods rather than flexible wires, and are customarily made from a refractorymetal such as tantalum, tungsten or molybdenum.

As the legs of..the M:filarnent are all in thesame plane, theshape of the anode and grid is preferably that of a flattened cylinder so that the fiat faces of the anode and grid are exposed to the" electron stream. Few electrons are drawn to the rounded lateral surfaces ofthe anode and the grid wires between these surfaces and the cathode are not effective in the control of the electrons, the main heating of the anode and grid taking place on the flat faces. This action is well known in the art and can be visuallytdemonstrated in tubes having elements of this shape by overloading the tube until the anode glows at a red heat. The glowing will appear on :the anode .faces parallel tOthBflDlEiIlG of .the filament.

We prefer therefore to solidly connect and separate the two spacing members I! by welding the ends of certain of the grid elementsito bothof :the members to 'forma supporting frameworkfor the remainder. These grid support elements 2| are placed substantially in :the plane of thefilament, out of the electron stream and in the type of tube shown,.in the rounded corners on each side of .the grid structure.

We then weldtheends of the remainder of the grid elements, hereafter called grid control elements 22, alternately to the spacing members in staggered relation so that only one end of each end passing freely through ;the.opposed aperture in the other spacing member. There is thus formed a complete cylindrical made up of the parallel control elements, the spacing members, and the support elements. Thiscage is placed in 'the 'tube between the anode and cathode so that the freely expansible control elements are the only'ones in the electron stream and subject to extensive variationsof'heat.

The entiregrid structure maybe-supported in any welleknown manner, but-we prefer-toweld an elbow 24 toithe top andbottom spacing members i and connect :the outer ends of these elbows to grid struts 25 sealed through-the envelope in lateral envelope projections 26 opposite theanode projections 15, and "then provide these projectionsnwith gridlconnection capsfl connected to the grid struts. I

i In operation the tube is energized, and the support elements 2l' -will thereupon expand slightly duev to heat #from the filament and general operating temperatures. If these support elements should depart from parallelismslightly no harm willbedoneas they haveno substantial control'over the electrons. As one end of all :the control elements is :free in an aperture ofv one :of .the spacing members, this original expansion will .not disturb their. relationship to each other.

other. however, 'in that it makes for During Ifurther operation, power' peaks, and heavy loads may-be imposed on *the tube, but the control elements are free to expand through the apertures of the spacing members and do so, thus preventing buckling. Any buckle would open a wider gap between two of the elements, and reduce the effective control of the grid as a whole.

It is, of course, not necessary that the control elements be alternately welded to ,the spacing members. They may all be welded toone memher, and extend through the apertures in the The alternate construction is preferable, ease of assembly, and there is more room for welding. Furthermore, the welding operation virtually closes the apertures and .a support member having alternate apertures closed by welding is stronger than one in which all the apertures remain open.

"While we :have shown the grid as constructed of vertical ,parallel grid elements, it may be desira'ble to place the spacing members I! on the sides of :the cathodelwith the control elements extending horizontally. In this case, the support elements 21 of the gridmay be separated for the cathode leads 4 and :the spring hooks 6, placing the support members above and below the electron stream. The'operation is the same although the horizontal positioning is not preferred in tubes of extreme high power due to the tendency of the control elements to sag under the influence of gravity, when heated above a red heat.

In the structure here shown and described the support elements 2! which connect the two spacing members I] are identical with the control elements 2-2 both in dimensions and spacing. It is obvious however that as they are removed fromthe direct electron stream, that a single larger r'od may be substituted, or like connection, :without violating the spirit of'our invention.

-We claim:

1. A vacuum tube grid comprising a pair of conductive support members having a series of apertures therein, conductive means for spacing said support members, and a-plurality of parallel grid wires extending between said support members through said apertures, said wires being solidly fastened in alternate apertures of one of said support members and free" to expand through the remaining apertures, said support members providing the sole electrical connection between said wires.

2. In combination a vacuum tube comprising an envelope, a cathode lying in a plane, a plural ity of vertical 'wires-surroundingsaid cathode and arranged to form a grid of substantially rectangular cross'section, upper and lower conductive supports for said wires said supports having a series'of apertures therein, the vertical wires located at :the;narrow edges of-said grid "being solidly fastened to-both of said supports and the wires locatedinthe broad surfaces of said grid parallel to .the plane of saidcathoderbeingsob'

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