US2015327A - Electron discharge device - Google Patents

Description

Sept. 24, 1935. H. A. WHEELER ELECTRON DISCHARGE DEVICE Filed Jan. 30, 1935 TTo RNEY5 Patented Sept. 24, 1935 ELECTRON DISCHARGE DEVICE Harold A. Wheeler, Great Neck, N. Y., assignor to Hazeltine Corporation, a corporation of Delaware Application January 30, 1933, -Serial No. 654,327

Claims. (Cl. Z50- 27) UNITED STATES PATENT oFFicE This invention relates to electron discharge Y devices, and more particularly to devices of this character having five or more electrodes.

It is an object of this invention to provide a device which is particularly well-adapted to perform the function of modulation. A related object is to provide a modulator valvewhich can be readily controlled by means of a grid bias voltage.

In a preferred embodiment for carrying out the above objects, there is provided a vacuum tube having six electrodes, namely, an electronemitting cathode and a plate, or anode element, in the space path between which are located four other electrodes. These four latter electrodes are in the form of screens and grids and are located at successively increasing distances from the electron-emitting element, the rst of these screens and grids being designated as closest to the said emitting element.

The term grid or grid-like electrode", as used in the specification and claims, denotes an electrode by which, or through which, electrons may pass. The term screen denotes a form of grid-like electrode by which, or through which, electrons may pass and which ordinarily is maintained at a substantial positive potential with respect to the actual cathode.

A feature which makes the device according to this invention particularly well suited as a modulator is the construction of the grid which is the third of these screens and grids in point of distance from the cathode; this grid is formed of a mesh having a variable spacing or pitch. It is preferable that the greater portion of this third grid be of relatively fine mesh, or pitch, although a substantial portion may be of much coarser' mesh.

The second of these interposed electrodes in point of distance from the cathode is a screen preferably constructed with a ne mesh or pitch.

The fourth of these interposed screens is incorporated for use as an ordinary screen-grid; and it is found that the device is operative when this fourth screen is omitted.

In the drawing:

Figure l illustrates an electron discharge device in accordance with this invention, a portion of the glass-enclosing vessel being cut away to show more clearly the position of the electrodes within;

Fig. 2 is a vertical sectional view of the device showing in detail its construction and the'positions of the elements;

Fig. 3 is a broken diagram showing in perspective the construction of the elements and also indicating the manner of connecting operating voltages which place the device in an operative condition; v

Fig. 4 is a plan View, in section, of the electrode 5 construction; and

Fig. 5 is an enlarged illustration, partially in section, of the cathode electrode and the means for heating the same.

Referring to Figure 1, the device comprises an l0 evacuated glass bulb I0, the stem end of which is fitted into a bakelite base II in which are embedded seven projecting terminal lugs, numbered I2 to I8, respectively, adapted to fit into a suitable socket. An eighth terminal I9 is situated l5 at the top of the bulb in the form of a metallic cap cemented to the glass. The electrodes of the device are supported by a number of Vertical supporting wires embedded in a glass stem 20 formed on a reentrant portion 2I at the stem end of the 20 bulb (see Fig. 2). For the purpose of maintaining the supporting wires rigidly in their upright position, there are provided two flat guides 22 and 23 of an insulating material, such as mica. through which the supporting wires project. The upper 25 guide 22 is constructed to snugly iit within the dome-like end of the glass bulb.

The following electrode construction is employed: A cathode I in the form of a sleeve of very small diameter is centrally located within the bulb. This sleeve is preferably constructed of nickel coated with strontium and barium oxides for the purpose of causing it to copiously emitelectrons when heated. For the purpose of heating the cathode sleeve, there is located within the sleeve a heater filament 38 of ne wire, preferably of tungsten, coated with ceramic insulation and threaded back and forth within the sleeve in the form of a W as shown in Fig. 5. The ends of the heater filament are connected to the large- 4o diameter terminal lugs I2 and I3 at the base.

vgrid-electrode 2 and also of the remaining electrodes about to be described. The major axis of each ellipse is only slightly greater than the minor axis. v

A second grid-like electrode 3, here called an inner screen, is constructed in the form of an elliptical cylinder by winding a helix of wire which surrounds the first grid.2, the second gridlike electrode being supported on the two supporting wires 26 and 21. This second helix is of fine mesh, that is, has a small pitch, which is preferably uniform throughout.

A third grid electrode 4, here called an outer grid, surrounds the electrode 3, and is likewise formed by a helix of wire in the shape of an elliptical cylinder supported on supporting wires 28 and 29; but the pitch or mesh of this electrode is not uniform throughout its extent. Throughout the greater portion, the pitch is very fine, but in one or more small ranges, thepitch is substantially increased. A construction of this third grid which has been found very satisfactory is one in which fifty turns of .004-inch diameter wire are wound so that the major axis is 0.360 inch and the minor axis 0.316 inch, the component turns, numbered from one end to the other, having the pitch indicated in the following table:

Turn Pitch 1-18 014 inch 10-20 018 2l O26 22-23 018 24 012 2526 0l8 27 050 28-29 018 30 034 31-32 01B 33-50 014 Surrounding this third grid, and supported on supporting wires 30 and 3I, is a fourth grid-like electrode 5, here called an outer screen, also constructed of a helix in the form of an elliptical cylinder. 'I'his fourth grid-like electrode preferably has a relatively fine mesh which is uniform throughout.

Finally, a plate 6, in the form of an elliptical cylinder, is provided which surrounds the entire grid-electrode structure, this plate being supported on supporting wires 32 and 33. The plate is preferably constructed of carbonized nickel and its axial length is not as great as that of the other electrodes.

From the foregoing description, it is observed that the first, second, third and fourth grid-like electrodes, designated 2, 3, 4 and 5, respectively, are located at succeedingly increasing distances, in the order named, from the cathode in the 'space path between the actual cathode and the Constructional data for the electrodes other than the third grid electrode, or outer grid 3, which have been found very satisfactory, are as follows:

Inner grid 2 major axis, 0.121 inch; minor axis, 0.96 inch; wound with25 turns of .004 inch diameter wire with a .033 inch uniform pitch.

Inner screen l-major axis, 0.236 inch; minor axis, 0.167 inch; wound with 33 turns of .005 inch wire with a .025 inch uniform pitch.

Outer screen i-major axis, 0.490 inch; minor axis, 0.460 inch; wound with 33 turns of .005 inch diameter wire, with a .025 inch uniform pitch.

The connection of operating voltages which place the device in a very advantageous operative condition, particularly for use as a modulator, is illustrated in Figure 3. There is connected across terminal lugs I2 and I3 a battery 34 (or other source of filament heating current) which serves to heat a W-type filament 33 within the cathode sleeve, the said cathode itself being nominally grounded by the ground connection at terminal I4. Batteries 35, 36 and 3l, or other sources of direct voltage are connected between ground and the terminals I6, I'l and I8, respectively, for applying l0 positive voltages to the inner screen 3, the outer screen 5 and the plate 6, respectively. A negative bias battery 39 is connected between ground and the cap I9 for placing a negative bias upon the non-uniform mesh, outer grid 4. l5

With the above-described system of operating voltages, the action of the device is as follows: The heated cathode I emits electrons which are attracted to the inner screen- 3 by virtue of the positive voltage applied to the latter. The elecil trons upon reaching the screen 3 are traveling at a high speed so that most of them pass on through the screen and approach the outer grid 4, the negative potential of which retards the electrons and causes most of them to be attracted back to the positive screen 3. This retarding action causes a cloud of slowly-moving electrons to accumulate between the electrodes 3 and 4. Hence, the position of this cloud may be termed n a virtual cathode because of the fact that the electrons can be easily drawn away from the cloud in the same manner that they were originally drawn away from the vicinity of the actual cathode I. Since the screen 5 and plate 6 are at a positive voltage, a stream of electrons is 3" drawn from the virtual cathode, through the meshes of the grid- like electrodes 4 and 5 to the plate. Electrodes 4, 5 and 6 function similarly to the respective control grid, screen and plate of screen-grid tetrode tubes. The outer screen 3 40 will usually have applied to it a source of positive voltage somewhat less than that of the plate in the preferred manner of screen-grid tubes.

The electron-discharge device in accordance with this invention has been found to be very 4" useful where it is desired to exert a control upon the action of a vacuum tube without actually introducing into a circuit or space path of that tube external elements which would not very successfully cooperate. For example, the repeating portion of the tube may be considered to have input terminals which are the outer grid 4 and the virtual cathode, and to have output terminals which are the plate 6 and the virtual cathode. Since the potential of the virtual cathode is the u" same as that of the actual cathode, it is found that input signals impressed between terminals I4 and I9 will be repeated at the output between terminals I 3 and I4.

The desired modification of the input signals can then be effected by applying the modifying voltage to the inner grid 2, that is, between terminals I4 and I 5. This modifying voltage may often be a simple alternating voltage, which then causes the entire device to operate as a modulator.' The effect of the voltage on the grid 2 is to modify the electron stream which flows to the virtual cathode and hence indirectly to modify the space current between the virtual cathode 70 and the plate.

Since the electrodes 4,` B-and 3 exert very little effect on the space current to electrodes 2 and 3, the inner and outer control grids 2 and 4 may be operated quite independently of each other. For u amasar plished without .affecting the action ot any modilying voltage applied to inner grid 2.- Thisvaria- .tion of the negative bias of the outer grid l is a very convenient expedient inasmuch as it permits a very simple control of the responsiveness of the device..

The non-uniform sise of the meshes of control grid I, commonly known as the variable-mu or gradual-cutoff type of grid, permits a wide range of bias voltage to be applied without causing signal distortion and withoutinterfering with the normal action of electrodes 2 and 3.

'I'he outer screen l may be omitted.' -but its presence greatly improves the results, particularlyA in obtaining the greatest responsiveness. This screen, in general, performs the function of a similar screen in the well-known screen-grid tetrode, and is therefore usually given a positive voltage somewhat less than that of the plate.

It is usually desirable to carbonize the inner wall of the glass bulb or vessel, as indicated in Figure 1 by the 'dotted portion of the glass; this, however, is a renement which may be omitted.

v I claim:

1. An electron discharge device adapted to function as a bias controlled signal translating device comprising a closed evacuated vessel containing a centrally located cathode, at least three substantially concentric cylindrical grid-like electrodes surrounding said cathode and being ofy succeedingly increasing diameters, and a cylindrical plate surrounding said electrodes, the third fromthe cathode of said electrodes having nonuniform grid spacings and having impressed thereupon a negative poipntial, and the second from the cathode of said electrodes having impressed thereupon a positive potential, whereby electrons drawn from said cathode form, in eiIect,

a virtual cathode between said second and third electrodes, the non-uniform grid spacings of said third electrode serving to permit a wide range of -bias voltage to be applied thereto without causing signal distortion and without interfering with the normal action of the innermost two grid-like e1ectrodes.

2. An electron discharge device adapted to function as a bias controlled signal translating device comprising a closed evacuated vessel containing a centrally located cathode, four substantially concentric cylindrical grid-like electrodes surrounding said cathode and of succeedingly increasing diameters, and a cylindrical anode surrounding the said electrodes, the thirdl from the cathode of said grid-like electrodes having a grid spacing which is non-uniform and having impressed thereupn a negative potential, and the second from the cathode of said grid-like electrodes having impressed thereupon a positive 'potentiaL whereby electrons drawn from said electrons are drawn to said anode from said 5 virtual cathode. thenon-uniform grid spacings y ofsaid third electrode serving to permit a wide range of bias voltage to be applied thereto without causing signal distortion and without interfering with the normal action o! the two grid- 10 like electrodes nearest the cathode.

3. An electron discharge device accordin to claim 2 in which the grid spacing of each of' said lectrodes, except said third electrode, is uni'- orm.-

4. Anfelectron discharge device adapted to function. as a bias controlled signal translating device, comprising a closed vessel containing a cathode, at least three grid-like electrodes near said cathode and located at succeedingly increas- 20 ing distances from said cathode, and a plate substantially surrounding said cathode and said electrodes. the third from the cathode of said electrodes having non-uniform grid spacings and having impressed thereupon a negative potential, .25

.and the second from the cathode of said elec- Aing to permit a wide range of bias voltage to be applied thereto without causing signal distortion and without interfering with the normal action of the innermost two grid-like electrodes. 5. An lelectron discharge device adapted to function as a bias controlled signal translating device comprising a closed evacuated vessel containing a cathode, four grid-'like electrodes near said cathode and located at succeedingly increas- 4o ing distances from said cathode, and an anode substantially surrounding said cathode and said electrodes, the third from the cathode of said grid-like electrodes having a grid spacing which is non-uniform and having impressed thereupon a ,negative potential, and the second from the cathode of said grid-like electrodes having impressed thereupon a positive potential, whereby electrons drawn from said cathode form', in effect, a virtual cathode between said second and third electrodes, and a positive potential applied to the fourth from the cathode of said grid-like electrodes and to said anode, vwhereby electrons are drawn to said anode from said virtual cathode, the non-uniform grid spacings of said third electrode servingI to permit a wide range of bias voltage to be applied thereto without causing signal distortion and without interfering with the normal action of the two grid-like electrodes nearest the cathode.

HAROLD A.

Images