US2277863A - Electron discharge device and circuit - Google Patents

Description

March 31, 1942. I a. w. HEROLD Original Filed April 28, 1937 Z Sheets-Sheet 1 INVENTOR v V EDWARD- HEROZD wrw,

ATTORNEY tab 31, 1942.

2 Sheets-Sheet 2 Original Filed April 28, 1937 INVENTOR EDWARD 14/. HEROLD ATTORNEY Patented Mar. 31, 1942 UNITED [STATES rATEr ICE ELECTRON DISCHARGE DEVICE AND CIRCUIT Edward W. Herold, Verona, N. J., assignor to Radio Corporation of America, a corporation of Delaware 5 Claims.

My invention relates to electron discharge devices particularly suitable for superheterodyne reception and circuits, therefore, and more particularly to a multi-electrode electron discharge device in which local oscillations of predetermined frequency and input oscillations of a different frequency, such as a radio signal, are mixed or combined within the device.

The present application is a division of my copending application Serial No. 139,375 filed April 28, 1937, Patent No. 2,219,102 October 22, 1940, and assigned to the same assignee as the present application.

In radio receivers employing the superheterodyne method of reception alternating voltages of two different frequencies must be combined; that is, the signal voltage of one frequency received by the antenna and usually amplified in the preceding stage must be combined with the local oscillator voltage at a different frequency produced by the local oscillator in the receiver proper so that a heterodyne action will produce an alternating voltage of an intermediate frequency modulated in the same manner as the signal voltage.

Usual methods of a heterodyne reception employ a first detector or mixer tube in which the radio signal (input frequency) and the local oscillations of a different frequency generated in an oscillator circuit usually by a separate tube are both applied to the same tube but on different grids. This mixing action in modern receivers may be accomplished by means of two different types of tubes, one the so-called pentagrid converter, which has several grids, the oscillator grid being the inner grid near the oathode and the signal grid being an outer grid. This tube performs both the functions of the oscillator and mixer. The converter type of tube in which both functions are performed meets with several difficulties, the two major ones being space charge coupling between the oscillator and signal sections, and the change of oscillator frequency when automatic volume control voltage is applied to the tube. These difficulties were overcome to a certain extent by placing the signal voltage on an inner grid and the oscillator voltage on an outer grid. This method of operation, however, prevented a tube design which could combine the functions of an oscillator and mixer in the same section of the tube due principally to the fact that the oscillator would cease functioning when the signal or control grid became sufficiently negative to cut off the electron stream to the oscillator portion of the tube. For high frequencies, therefore, it was found more desirable to use the so-called straight mixer tube having a signal grid and an oscillator grid to which the oscillator voltage is applied by a separate tube or a separate group of electrodes in the same envelope effective as a separate tube to provide the oscillator voltage.

When the higher frequencies were encountered, however, it was found that even the mixer tube was subject to certain objections because of the transit time effect in the tubes which caused grid current to flow in the first or signal grid when the second or oscillator grid voltage was high in frequency. This effect is explained as due to the electrons which are periodically repelled by the oscillator grid when it goes negative; that is, electrons which are in the space between the signal grid and the oscillator grid when the oscillator grid swings negative are returned to the signal grid. It was also discovered that the signal grid input resistance wasquite low at the high frequencies and most of this socalled transit time loading was also due to the electrons repelled by the oscillator grid to the Vicinity of the first grid.

It is the principal object of my invention to' provide an improved type of mixer tube for use in superheterodyne receivers, more particularly to provide such a tube in which the transit time -eifects described above are substantially elimi-' nated.

The novel features which I believe to be characteristic of my 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 drawings in which Figure 1 is a transverse cross section of the mount of an electron discharge device illustrating and embodying the principles of my invention; Figure 2.

is a practical form of an electron discharge device made according to my invention; Figure 3 is a perspective view partially in section to show details of construction of an electron discharge device which has been found most satisfactory; Figure 4 is a cross section taken along the line 4-4 of Figure 3; Figure 5 is a cross section of the mount of a still further modification of an electron discharge device made according to my invention; and Figure 6 is a conventional circuit in which an electron discharge device made according to my invention is incorporated.

In the conventional mixer tube such as shown in the Llewellyn Patent 1,876,780, issued February 7, 1933, and assigned to the Bell Telephone Lab-' oratories the cathode is surrounded in turn by a signal grid, a screen grid, an oscillator grid to which the local oscillation is applied, and a second screen grid, and an anode. At very high frequencies the time required for the electrons to travel from the cathode to the anode is long enough so that electrons may be caught in flight between the signal grid and the oscillator grid when the oscillator grid goes negative. These electrons are sometimes repelled by the negative oscillator grid and return to the signal grid with an appreciably increased velocity. By means of my invention the electrons which are repelled by the oscillator grid are swept out of the space between the signal grid and oscillator grid and prevented from returning to the signal grid.

A better understanding of the action may be obtained by referring to Figure 1 showing a cross section of a mount of a tube embodying the d principles upon which my invention is based. A cathode I8 is surrounded in turn by a signal grid ll, screen grid [2, oscillator grid 13, screen grid l4 and anode [5. A suppressor grid Hi can be added if desired. Each of the grids is provided with oppositely disposed side rods, the side rods lying in a common plane. With the construction so far described, which is the conventional mixer tube, the electrons are projected in two more or less well defined streams or beams from opposite sides of the cathode due to the action of the signal grid side rods. In normal operation when the oscillator grid 13 is swung negative by the applied oscillator voltage, the electrons are prevented from reaching the anode l5 and are returned to the region of the signal grid through the screen grid I2 which is at a high positive potential. The effect of the returned electrons is to cause the signal grid to exhibit a very low input resistance at high frequencies. In addition, some of the electrons have appreciably increased velocities because of the change in oscillator grid potential during the time the electrons are in the region between grids l2 and I3. The increased velocity is sometimes suflicient to permit electrons to strike the negatively biased signal grid H.

In accordance with my invention I place between the signal grid and oscillator grid, and in line with the side rods, a pair of auxiliary electrodes H, which are maintained at a high positive potential with respect to the signal grid and the oscillator grid and being preferably at a higher potential than the screen grid l2. The result of this applied voltage is to cause the stream of electrons on either side to travel in more or less curved paths as indicated by the dotted lines from the cathode to the anode. It will thus be seen that most of the electrons are made to pass considerably closer to the side rods than when the electrodes [1, I! are not present. Electrons caught between the signal grid and the oscillator grid under these conditions will not return to the region of the signal grid but will be returned as indicated by the dotted lines to the auxiliary electrodes I1 ,I 1, which are at the higher positive potential. These returning electrons are indicated for only one-half of the tube, it being understood that this action takes place on both sides. In this way the electrons which would normally be returned by the oscillator grid going negative are swept from the field between the signal and oscillator grids and are rendered ineffective to cause grid current and low signal resistance.

but much larger auxiliary anodes.

In Figure 2 a modified form of tube is shown which is an improvement over that shown in Figure 1 The form shown in Figure 2 eliminates the necessity for separate auxiliary electrodes and the necessary leads and results in a simpler construction in which the high potential small auxiliary anodes are replaced by lower potential In this arrangement the cathode 20 is surrounded by a control grid 2| and screen grid 22, followed in turn by the oscillator grid 23, scren grid 24, suppressor 25 and anode 26. In this form the auxiliary electrodes 21 and 28 have the form of channel members attached on the outside of the screen grid to the screen grid side rods so that oppositely disposed slots are provided for the electrons issuing from the cathode. This construction also has the advantages characteristic ofthe form shown in Figure l, but is in addition simpler in construction.

The preferred embodiment of my invention disclosed in Figure 3 and embodied in a tube oi the metal envelope type includes a metal envelope 30 in which the mount assembly is contained. The mount is positioned between a pair of shielding members 3| and 32 supporting the mica insulating spacers 33 and 34 which insulatingly support and space the electrodes from each other. As best shown in Figure 4, the cathode comprises a tubular member 35 of rectangular cross section. The fiat opposite sides only preferably are coated, which assists in the beam formation of the electrons from the oathode to the anode. The cathode in turn is surrounded by a control grid 36, the wires of which are parallel to the fiat coated surfaces of the cathode, the side rods 36' being opposite the noncoated surfaces of the cathode, a screen grid 31, oscillator grid 38, screen 39, suppressor 40 and anode 4|. The collecting electrodes or auxiliary electrodes 42 are in the form of channel members electrically connected to the screen grid side rods and oppositely disposed to provide a pair of oppositely disposed slots or apertures through which the beams of electrons from the cathode are directed toward the anode. This form of tube made according to my invention is an improvement over that shown in Figures 1 and 2.

A still further modification of my invention is shown in Figure 5 wherein the oscillator grid 44 is provided with a pair of oppositely disposed side rods 45 positioned in the electron beams and open spaces or slots between the auxiliary collector electrodes 42. These rods assist in causing the primary electrons from the cathode to travel a curved path and further insure that electrons returned by the oscillator grid are returned to the solid shield auxiliary electrodes on the screen grid. Only a part of the electron stream is shown by slotted lines to indicate the paths of electrons which reach the plate and those that are returned to the collecting electrodes or shields 42. This still further improves the operation of the tube shown in Figures 1 and 2.

The application of a tube made according to my invention to a conventional circuit is shown in Figure 6 in which the tuned circuit comprising the inductance 50 and variable capacity 5| is connected between cathode 35 and control grid 36. The screen grids 3! and 39 are connected to the usual source of voltage 40, the oscillator grid 38 being connected to a separate local oscillator 52. The output from the anode is fed through the primary of the coupling transformer 53.

While I have indicated the preferred embodiment of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my 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 my invention as setl forth in the appended claims.

What I claim as new is:

1. In combination, an electron discharge device having a cathode and a control electrode adjacent thereto for providing a stream of electrons, an anode for receiving said electrons, a second control electrode positioned in the stream of electrons between said first control electrode and said anode, means for impressing a variable potential on said second control electrode effective to cause diversion of a varying number of electrons from said stream, and means positioned between the first and second control electrodes at the side of the electron stream for receiving electrons diverted by said second control electrode, said last named means being directly exposed to the second control electrode.

2. An electron discharge device having a thermionic cathode for supplying a stream of electrons, an anode for receiving said stream of electrons, a first control electrode adjacent said cathode for controlling movement of electrons in said stream from said cathode to said anode, a second control electrode between said first control electrode and said anode, and means for applying a varying negative and positive voltage to said second control electrode, and means outside of and to one side of said stream of electrons and between said first and second control electrodes for receiving electrons returned by said second control electrode when a negative potential with respect to said cathode is applied thereto during operation of said electron discharge device, a circuit connected to said first control electrode and a circuit connected to said anode.

3. An electron discharge device having a thermionic cathode for supplying a stream of electrons and an anode for receiving said stream of electrons, a first control electrode, means for applying a varying voltage to said first control electrode, a screen electrode and a second control electrode in succession between said first control electrode and anode, and means for applying a varying positive and negative potential to said second control electrode, and means between the screen electrode and said second control electrode and positioned outside and to one side of said stream of electrons for receiving electrons returned by said second control electrode when said second control electrode becomes negatively charged during operation of said electron discharge device, and a circuit connected to said anode.

4. An electron discharge device having a cathode and a control electrode adjacent thereto for providing a stream of electrons, a circuit connected to said control electrode, an anode for receiving said stream of electrons, a second control electrode positioned in the stream of electrons between said first control electrode and said anode, and circuit means for applying varying positive and negative potentials to said sec-.

ond control electrode, and means positioned at one side of said stream of electrons and between said first and second control electrodes for receiving electrons returned by said second control electrode when said second control electrode becomes negative, and a circuit connected to said anode.

5. An electron discharge device having a cathode for supplying electrons and surrounded by a first control grid, a screen grid, a second control grid and an anode, said first control grid being provided with oppositely disposed side rods whereby electrons from said cathode move in two oppositely disposed beams between said side rods to said anode, a circuit connected to said first control electrode, and means for applying to said second control electrode a varying negative and positive potential and means on opposite sides of said beams between the two control electrodes for receiving electrons returned by said second control electrode when a negative voltage is applied to said second control electrode, and a circuit connected to said anode.

EDWARD W. HEROLD.

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