US2159765A - Electron discharge device - Google Patents

Description

May 23, 1939.- J. L. H. JO'NKER ET AL 2,159,765

I ELECTRON DISCHARGE DEVICE Filed May 2'7, 1938 E: b v.

IIII 11111 11 INVENTORS JOHAN L.H. JONKER BY BERN DUS O.M GALL ATTORNEY.

Patented May 23, 1939 UNITED STATES PATENT OFFICE s f 2,159,765 ELEGTRONI DISCHARGE. DEVICE.

2 Claims. (Ci. est-27.5)

This inventionrelates to a multi-grid electron .discharge tube having a plurality of control grids andxparticularly suitablecas a so-called mixer jlfltube in superheterodyne circuits. The invention *5 Siurthermore relates to such a tube and to a circuit in which such a tube can be used.

{In theconventional tubes of thistype ordinarily between a cathode and an anodela number of grid-shaped electrodes are arranged of which 10. two are employed as control grids,'one on which i the received signal voltage is impressed and the other on which the local oscillator voltage is impressed. The two control grids are disposed ordinarily directly behind one another which involves j lthe, disadvantage that these grids have a high I capacity relative to each other. a

i To reduce this capacity in tubes having a pair of control grids such as for instance the mixer tubes, and octodes, at least one grid serving as a 20 screen grid and having a positive potential is 1 positioned between the control grids. In this case the second control grid usually does not control f directly the electrons leaving the cathode but controls a space charge, a s-ca1ledvirtual cathi ld olde, which forms between the positive screen electrode and the second control grid. Though with this arrangement favorable results can generally be obtained, in certain cases suchtubes have the disadvantage that due to'the space I l charge which is influenced by the second control grid, a current distribution appears which among other things causes a considerable increase of the rustling noises developed in the tube.

[ j Applicants have found that this disadvantage 35 can be overcome when employing an arrangement and an electron discharge tube in accordance with the present invention. According to our invention a tube having two control grids has positioned betweenthe grids instead of a screen elec 40 trode, at a positive potential, screens between a parts of the control grids, these screens being connected to a point having zero potential or a fixed negative potential.

{Since the control is exerted upon two successive grids so that both control'grids influence 50 posed between parts of the grids and are suitably connected to a point having zero potential such as {for instance the cathode. These screens are then usually arranged between places of the control grids at which very few. electrons appear, for instance in the case of an oval cathode at places opposite the narrow sides, or in the region of the grid side rods.

In order further to reduce the noise of a discharge tube in accordance with the present invention, in accordance with a specific mode of con. struction the grid situated at the anode side of the second control grid and which may serve as a screen grid is so designed that the effective parts of this grid are aligned with the effective parts of the second control grid. In other words, the

turns of the second control grid and the screen grid are aligned. In order to reduce the screen grid current further it is possible to align also 'some of all effective parts of control grid I. with those of the second control and the screen grids. l6 s A discharge tube and an arrangement according to the present invention are especially well suited for use in mixer circuits of an intermediate frequency superheterodyne receiving circuit.

In a discharge tube according to the invention and employed as mixer tube the first grid can be used as an input control grid, and the second control grid as an oscillator control grid, or vice versa, whereby the oscillations of the local oscillator may be produced by means of a separate'triode. In accordance with a certain mode of construction, according to the present invention, the mixer system and the triode may however also be combined to form a single tube. Such a tube contains in this case an indirectly heated cathode surrounded along a portion of its length by a single grid, and an anode, while there is placed about another portion of the length of the cathode an electrode system as described above and comprising two control grids with interposed screen main- 3 tained at zero potential or negative potential, a screen grid and an anode, whereby in addition an absorption or suppressor grid may be arranged between thescreen grid and the anode.

The novel features which we believe to be char- 40 acteristic of our invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which Figure 1 number of grid-shaped electrodes 2, 3, 4 and 5 surrounding and coaxial with said cathode and which are used respectively in a discharge tube, and an arrangement according to the present invention, as first control grid, second control grid, screen grid andabsorption or suppressor grid. Small screen plates 6, which may be of sheet metal, are arranged between the grids 2 and 3 and at places, i. e. between parts at which but few electrons appear, in comparison with the other parts of the grids. The various grids are fastened to supporting rods 1 which all lie in the same plane to provide a field distribution as favorable as possible. Finally, an anode 8 is placed about the said grids. The electrode assembly is placed within an evacuated envelope 8'.

Figure 2 shows a circuit in accordance with the present invention. In this circuit two tubes 9 and ID are shown of which the first one is employed as triode oscillator, containing a cathode I I, a grid [2 and an anode I3, while the second tube represents a mixer tube in accordance with the invention, containing a cathode I, two control grids 2 and 3, a screen grid 4, an absorption grid 5 con nected to the cathode, then an anode 8, and two small screen plates 6 likewise connected to the cathode. In the drawing there is shown furthermore an input circuit 2 I, an output circuit 22, and

an oscillatory circuit 23 whereby the oscillations produced in the tube 9 are impressed upon the grid. l6 of the tube ID to provide a voltage of intermediate frequency in output 22.

. While we have indicated .the preferred embodiments of our invention of which we are now aware and have also indicated only one specific application for which our invention may be employed, it will be apparent that our invention is by no means limited-to the exact forms illustrated or the use indicated, but that many variations may be made rods lying in a common plane, and a pair of shielding members positioned between the control grids and lying adjacent said side rods and providing openings on opposite-sides of said cathode through which electrons from said cathode may travel to said anode.

2. An electron discharge device having a straight thermionic cathode and an anode surrounding said straight thermionic cathode, a pair of control grids surrounding and coaxial with said cathode and positioned between the cathode and anode, and a screen grid surrounding said control grids, each of said grids being provided with a pair of side rods,said side rods lying in a common plane, and a pair of V-shaped shielding members positioned between the control grids and lying adjacent said side rods and providing openings on opposite sides of said cathode through which electrons from said cathode may travel to said anode, said shields connected to cathode.

JOHAN LODEWIJK HENDRIK JONKER. BERNARDUS OCTAVIANUS MARIA GALL.

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