US2118922A - Electron discharge device - Google Patents

Description

May 31, 1938. D. G. HAINES ET AL ELECTRON DISCHARGE DEVICE Filed Sept. 24, 1936 INVENTOR DONALD G. HAINES 6, BY KENNETH c1. BUCKLIN Patented May 31, 1938 UNITED STATES PATENT OFFICE ELECTRON DISCHARGE DEVICE Application September 24, 1936, Serial No. 102,280

4 Claims.

Our invention relates to electron discharge devices, more particularly to improvements in multigrid tubes of the so-called mixer or converter type, which are used in superheterodyne circuits, to

supply the local oscillator frequency and mix it with the radio input frequency to provide the desired intermediate frequency.

In the conventional type of converter tube, the cathode which may be of the filament or indi l0 rectly heated type is surrounded in turn by the oscillator grid, the oscillator anode rods, the screen grid, control grid, suppressor grid and the output anode. The grids are provided with oppositely disposed side rods which with the oscillator 16 anode rods are parallel and aligned so that they lie in a common plane. The local oscillator circuit is connected between the cathode and the oscillator grid, the oscillator anode rods being coupled to this circuit to feed back energy to pro- 20 duce the local oscillations. The signal grid or control grid is connected to be responsive to the input signal or radio input frequency. The tube mixes the radio input frequency and local oscillator frequency the result appearing as an inter- 26 mediate frequency, the output circuit being connected to the main or output anode.

In tubes of this kind the functioning of the oscillator portion of the tube is dependent upon the energy fed back to the local oscillator circuit 30 connected between the cathode and the oscillator grid, this energy feed back being dependent in turn upon the change in current in the oscillator anode circuit with change in oscillator grid voltage, that is, upon the transconductance of the 35 oscillator portion of the tube.

The current in the oscillator anode circuit depends upon the number of electrons captured by the anode rods as the electrons move from the cathode through the screen grid to the output 40 anode. The screen grid surrounding the anode rods is at relatively high potential urging the electrons toward it and the output anode and since the field of influence of the anode rods is small due to the small diameter of these anode 45 rods the current in the oscillator anode circuit is small and hence the amount of energy fed back to the oscillator portion of the circuit is limited since the change in oscillator anode current is small. In tubes of conventional construction as therfrequency at which the tubes operate is increasedjthe energy fed back decreases until at the higher frequencies oscillation practically ceases, due to the decrease lnthenumber of electrons reaching the anode rods. The close spacing required between the electrodes in the conventional tube introduces practical difficulties in construction when an attempt is made to increase the oscillator anode current by increasing the diameter of the oscillator anode rods to increase the sphere of their influence on the electrons.

It is, therefore, the principal object of our invention to provide an electron discharge device of the type described in which the electrical characteristics, particularly the transconductance, are better than in conventional tubes of like dimensions and which is particularly suitable for operation at high frequencies.

The novel features which we believe to be characteristic 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 is a side view with parts broken away to show details v of construction of an electron discharge device embodying our invention; Figure 2 is a section transverse to the longitudinal axis and taken along the line 22 of Figure 1; Figure 3 is similar to Figure 2 and graphically shows the operation. of the electron discharge device shown in Figures 1 and 2; Figure 4 is a conventionalcircuit for use with a tube embodying our invention.

In Figure 1 the electron discharge device comprises the envelope lfl provided with a cap H and conventional base, the envelope being provided with a re-entran't stem and press l3 upon which the electrode assembly is mounted.

The electrode mount assembly includes the filament cathode l4 surrounded in turn by the oscillator grid l5 having side rods l5, screen grid l6 having side rods I6, control grid ll having side rods I1 and electrically connected by means of the lead 18 to the cap II. A screen grid l9 having side rods [9' may be provided between the control grid I7 and the anode 2!]. These elec- 21b trodes are assembled and supported between mica spacers 2i and 22 with the side rods parallel and in alignment.

v In accordance with our invention we provide an oscillator anode having elements of novel construction and interposed between the oscillator grid 14 and screen grid l6. These oscillator anode elements are preferably in the form of flattened rods or legs 23 and 24 of fiat rectangular cross section and mounted in line with the aligned side rods of the grids, the planes of the fiat rods being perpendicular to a plane passing through the aligned side rods of the grids. The transverse section of the oscillator anode rods could of course be curved or of some other shape so long as the 5 rods have an extended surface transverse to the plane of the grid side rods. These legs may be electrically connected to form an anode, preferably by a U-shaped member 25 having a lower outwardly bent bottom portion 26.

In operation electrons leaving the cathode l4 travel outwardly through the oscillator grid and the succeeding grids to the output anode .20. A portion of these electrons, however, follow orbital paths such as shown by the dotted line in Figure 3, and are collected by the oscillator anode rods. It will be apparent that with the conventional round rods of small diameter the sphere of influence of these rods would be limited and due to the high potential on the screen grid the influence of the screen grid side rods would be as great or greater than the oscillator anode rods, so that the number of electrons reaching the oscillator anode rods would be limited. With our invention, however, the fiat oscillator anode rods extend beyond the screen grid side rods and more or less effectively screen the screen grid side rods from the cathode filament. This construction increases their field of influence and results in greater flow of electron current to the oscillator anode rods, particularly when these rods are at their peak positive potential. This increases the transconductance of the tube because anode current changes which take place for given oscillator grid voltage changes are greater than in tubes of conventional construction. The influence of the anode rods made according to our invention persists at the higher frequencies and hence oscillator anode current continues to flow and the oscillator circuit continues to function at much higher frequencies than in the conventional tube with round anode rods.

An application of a tube made in accordance with our invention to a converter circuit is shown in Figure 4. A tuned circuit comprising inductance 30 and variable capacity 3| is connected between the cathode M and the oscillator grid l5. Electrons collected by the oscillator anode rods 23 and 24 cause a flow of current through an inductance 32 and thus provide an energy feed back arrangement to the grid l5 so that the cathode with grid l5 and oscillator anode rods 23 and 24 form an oscillating circuit for generating the local oscillator frequencies thus modulating the electron stream passing through to the other grids to the anode 20. The signal voltage is applied from a signal source 33 tothe signal grid H, the proper positive voltages of course being applied to the anodes and the screen grid.

An electron discharge device made in accordance with our invention has improved electrical characteristics, particularly oscillator transconductance, which permit its use at higher frequencies than the conventional tube of the converter type depending upon electron coupling, while at the same time permitting a conservation of space within the electrode system.

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 in the particular structure used and the purpose for which it is employed without departing from the scope of our invention as set forth in the appended claims. 5

What we claim as new is:

1. An electron discharge device having an envelope containing a cathode and at least one grid and an anode forming the amplifier portion of the tube, and a second grid and a second anode 10 forming the oscillator portion of the tube, said grids being concentric and each of said grids having a pair of oppositely disposed side rods, said side rods being aligned, said second anode being positioned between said grids, and comprising a 15 member parallel to and in line with said side rods and having an extended surface transverse to a plane passing through said aligned side rods.

2. An electron discharge device having a cathode, a grid surrounding said cathode, a second 20 grid surrounding said cathode and first grid, and a third grid surrounding said cathode and first and second grids, each of said grids being provided with oppositely disposed side rods, said side rods being in alignment, an anode surrounding 25 the cathode and all of said grids, and a second anode electrode positioned between said first and second grids and comprising a fiat member of rectangular cross section, said last anode electrode being in line with said side rods and lying -3 in a plane perpendicular to a plane passing through the aligned side rods.

3. An electron discharge device having an envelope containing a cathode and at least one grid and an anode forming the amplifier portion of #3 the tube, and a second grid and a second anode forming the oscillator portion of the tube, said grids being concentric and each of said grids having a pair of oppositely disposed side rods, said side-rods being aligned, said second anode comr40 prising a pair of fiat conducting members parallel to the side rods and in line therewith and positioned between said grids the planes of said fiat conducting members being perpendicular to a plane passing through said aligned side rods, 54;?) said fiat conducting members extending beyond the side rods in a direction perpendicular to the plane passing through said side rods.

4. An electron discharge device having an envelope containing a cathode and at least one grid mo and an anode formingv the amplifier portion of the tube, and a second grid and a second anode forming the oscillator portion of the tube, said grids being concentric and each of said grids having a pair of oppositely'disposed side rods, said side rods being aligned, said second anode comprising a pair of flat conducting members parallel to the side rods and in line therewith and positioned between said grids the planes of said fiat conducting members being perpendicu- 560 lar to a plane passing through aligned side rods, and a grid positioned between the one grid and said second grid and flat conducting members and shielding the one grid from said second grid and flat conducting members. .65

DONALD G. HAIIQIES. KENNETH o. BUCKLIN.

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