US2115866A - Double grid electron tube and circuit - Google Patents

Description

`May 3, 1938. H, LUX 2,115,866

DOUBLE GrRID ELECTRON TUBE AND CIRCUIT Original Filed Nof. 16, 1932 Egli Z i|||| Hun." i

TPA ASQM/ 7' 7' EE RECEIVED INVENTOR HEINZUX BY )fg mm, ATTORNEY Patented May 3, 1938 DOUBLE GRID ELECTRON TUBE ANDl CIRCUIT Heinz Lux, Berlin, Germany, assigner to Telefunken Gesellschaft fr Drahtlose Teiegraphie m. b. H., Berlin, Germany, a corporation of Germany Original application November 16, 1932, Serial No. 642,845. Divided and this application May 27, 1936, Serial No. 82,001. In Germany November 17, 1931 6 Claims.

This application is a division of my application, Serial No. 642,845, filed Nov. 16, 1932, for Double grid electron tube andcircuit which has now matured into Patent No. 2,067,156.

In the methods discovered by Barkhausen and Kurz forproducing oscillations by means of braking fields, the electrons, as-is known, perform pendulum movements around the highly positive grid of a 3 electrode tube in which the anode has the potential of the cathode or a weak negative voltage. The electrons emitted by the lament participate, if they are not aifected by particular measures, only to the smallest extent in the pendulum movements, whereas the major amount of electrons move in a straight line towards the grid where they produce heat and thereby limit the loading capacity of the tube. The proportion between the grid losses and the oscillating power is about 100:1. An explanation for this phenomenon can be found when considering the electric eld between grid and filament, the shape of which is shown in Figure 1. All of the electrons which enter the straight or only slightly curved fields will move to the grid in a straightv line. Only at such places where the lines of force have a considerable curvature, the electrons do not follow the latter but maintain, due to their mass inertia, the straight path and then carry out the desired pendulum movements. Y p

The object of the present invention is to provide such field distribution so as to avoid as much as possible straight lines of force extending between the grid and the filament. As a result a larger-portion of the emitted electrons is caused to carry out pendulum movements and the supply of Ynon-oscillating electrons to the grid is reduced. This causes a decrease of the grid load and also an increase of the grid potential which in turn enables a decrease of the wave length.

In the drawing Fig. 1 illustrates diagrammatically the electric field between the several elec-- trodes of a three-electrode tube. Fig. 2 illustrates -diagrammatically a four-electrode tube o according to the present invention, and the electric field between the electrodes thereof. Fig. 3 illustrates a practical embodiment of the tube shown in Fig. 2 in connection with either a transmitting circuit or a receiving circuit. Fig. 4 is a detail view showing schematically the relation of one form of a pair of grids according to the invention, Fig. 5 is a transverse sectional view showing the relation of another form of a pair of grids according to the invention, and Fig. 6 is a view similar to Fig. 5 and showing a modification (Cl. Z50-27.5)

thereof. In order to obtain the desired field -distribution it is suggested to provide for instance a second grid between the filament and the positive grid electrode. In Figure 2 the filament is shown as l, the positive grid is shown as at 2 and the anode of a S-electrode tube is designated at 3. The wires of .the second grid li must be arranged in such manner so as to be on a straight line through grid 2 perpendicular with respect to anode 3 and lament I. When a spiral shaped grid is provided, two helices are obtained (Fig. 4)

which are of equal pitch but of a different diameter and the wires as such determine an-orthogonal screw surface. Where a rod shaped grid is used, as shown in Fig. 5 the single rods must be in .the same radial plane. When these require-A ments are fulfilled the field distribution follows the course shown in dotted lines in Figure 2. A deviation from this required arrangement would however be of detrimental eiect toa tube, as compared with a tube having only one grid. The grid 4 may either be connected .to the cathode, or may have a negative potential applied to it. It will charge negatively as a free grid and thus also fulfill its purpose.

In order to prevent the electrons from directly impinging upon the grid, a screen may be provided composed of dielectric materials such as mica, glass or quartz whereby the shape must be in accordance with the same principle as referred to above in connection with a metallic screen grid of the type shown in Figs. 4 and 5. In Fig. 6 there is shown the modification just described in connection with rod shaped grids. The screen of dielectric material is indicated by 2E and the positive grid of metal by 20".

The manner in which my improved double grid tube may be used in a transmitter is illustrated in Figure 3. Modulating audio frequency potentials from microphone 5 and audio frequency amplifier 6 are applied to the anode 8v through the transformer IIl. The secondary of transformer I I3 is connected in series with the lead I2 maintaining the anode at a highly or slightly negative potential with respect to the filament I4 which is energized to an electron emitting condition by the action of heater battery I6 and filament voltage adjusting resistor I8.

The grid 2li through which the electrons make their pendulum-like movements is maintained at a highly positive potential by the action of source 2l applying a positive voltage to it through lead 22. Chokes 24 are provided to prevent undesired iiow of high frequency current in the polarizing leads and sources.

The added grid 25 according to my present invention is maintained either at filament potential or at a slightly negative potential by the suitable tapping of lead 28 on to negative biasing source 30 or directly on to the filament lead 32. Oscillatory energy will then be developed in the Lecher wire system 30 tuned by the action of short circuiting condenser 32. A transmission line 34 may then be coupled to the Lecher wire system as shown so as to suitably load the same and feed into a radiating antenna 36.

Modulation is effected by Virtue of Variation in plate potential due to the action of transformer l in series with the plate 8. If desired, the secondary of the transformer IU may be inserted with similar effect in the lead 28 for the negatively maintained grid or grounded grid, or, in the lead 22 which maintains the grid 2U at a high positive potential.

It is to be noted that the perforations in the grids are arranged so as to be in line radially with respect to the filament. The alignment of the perforations is indicated by the dot and dash lines 40.

In the event that spiral grids are. used, they should be so wound as to be of the same pitch and arranged so that when viewed in cross-section, the cross-sections will be in similar alignment as indicated in Figure 4. In the event that a rod-like structure is used for grids, as shown in Figs. and

6, the rods 26 and 2U' of the respective grids in Fig. 5 and the rods 26" and 2D" of the respective grids in Fig. 6 should be arranged so that they lie, in cross-section, upon the same radial line running through the cylindrical cathode or filament.

If desired, as already indicated, the inner grid (26, 26 and 25") may be left floating, in which case electrons impinging thereon will give it the desired negative polarization.

Also, my improved tube may be used in a receiving system in which case antenna 36 would be a receiving antenna and the voltages and Lecher wire system 30 would be so adjusted that the tube would produce oscillations at the frequency of the incoming waves. Hence, by virtue of an autodyne effect audio frequency energy may be derived from transformer l amplified by an audio frequency amplier 6 and fed to a suitable translating device or loudspeaker 5. Here also, the transformer l0 may be placed in series with the other grid 26, or

in series with the positively maintained rgrid 20. Also, for receiving, it is not necessary that the oscillator oscillate at the mean frequency of the received waves. The tube may be adjusted by means of the voltages applied and the Lecher wire system to produce oscillations which will beat at a high frequency with the incoming waves. In that event, transformer I6 would be replaced by a radio frequency transformer and rectangle 6 would indicate apparatus including a second oscillator and second detector as well as, if desired, audio frequency amplifiers for actuating loudspeaker 5. Here also the radio frequency transformer l0 may be placed, if desired, in series with the inner grid 26 or outer grid 20.

What I claim is:

1. An electron discharge device comprising an electron emitting electrode, an electron receiving electrode in cooperative relation with said first electrode, said electrodes being disposed one within the other, and insulating means interposed between only the aligned portions of said electrodes for preventing the flow of electrons in a rectilinear path between said electrodes.

2. A Barkhausen oscillator comprising a cathode, an electrode in juxtaposition to said cathode, an electron receiving electrode intermediate said cathode and said first electrode, and insulating means adjacent said electron receiving electrode for preventing the. ow of electrons thereto in a rectilinear path from said cathode.

3. An electron discharge device comprising an electron emitting electrode, an electron receiving electrode, a third electrode outside of said electron receiving e1ectrode,and an insulating shield lntermediate said electron emitting electrode and all portions of said electron receiving electrode in alignment with said electron emitting electrode.

4. An electron discharge device comprising a linear cathode, an electrode including a plurality of wires disposed parallel to one another and to said cathode and mounted in a cylindrical boundary about said cathode, and insulating shielding means between aligned portions of said cathode and said Wires.

5. An electron discharge device comprising a cathode, an anode and a pair of grid electrodes Which have their grid wires in alignment in respect to the direction of electron flow, the grid electrode next adjacent the cathode being formed of dielectric material.

6. An electron discharge device comprising a cathode, a cylindrical outer electrode surrounding the cathode, a pair of grid electrodes concentrically arranged about thecathode and interposed in the space between the outer electrode and the cathode, the -grid electrode next adjacent the outer electrode being formed of conductive material, and the grid electrode next adjacent the cathode being formed of non-conductive material and disposed in the path of the electron flow from cathode to the conductive grid electrode whereby the electron ow between said electrodes in a rectilinear path is prevented.

HEINZ LUX.

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