US1744192A

US1744192A - Oscillator

Info

Publication number: US1744192A
Application number: US43221A
Authority: US
Inventors: Vladimir K Zworykin
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1925-07-13
Filing date: 1925-07-13
Publication date: 1930-01-21
Anticipated expiration: 1947-01-21

Description

Jan. 21, 1930. v. K. zwoRYKlN ATTORNEY Patented Jan. 21, 1930 UNITED STATES PATENT ori-ICE y VLALDIMIR K. ZWOIByYK-IN,l F WILKINSIBURG, PENNSYLVANIA, ASSIGNOR '.130v WEST- 4INGEO'USIZ. ELECTRIC `c MANUFACTURING COMPANY, A CGRPORATION 0F PENN- SYLVANIA OSGILLATOR vide an oscillator having two control electrodes. l 1.5 A still further object of my invention is to provide an oscillator having two cathodes. There are other objects of vmy invention which together with the foregoing, will be described in the followingv detailed specifiv cation.

In practicing my invention, I may employ a thermionic tube constructed in Ia manner `substantially similar to the thermionic tubes employed as radio detectors and amplifiers. That is, a tube having a hot cathode, a grid and a cold anode.` The construction, of course, may be modified in order to carry out my invention, as will appear subsequently. The single figure of the drawing isa crosssectional view of a preferred form of my photoelectric cell, 'an a diagrammatic view of associated circuits and apparatus.

My improved photoelectric cell comprises a glass bulb 1 having a deposit 2 of conducting material upon a portion of the inner surface of the wall thereof. The deposit may be platinum, or other suitable material, deposited from a'v solution, or applied in any other desired way.

A filament '3, a gridv` 4, a second4 gridv 5 and an anode 6 are disposed within the bulb in cooperative relation to each other. The grid 4 may be of the usual helical type employed in thermionic tubes, while the second grid 5 is preferably of finer mesh and is provided with an imperforate cap 7 and a depending skirt 8. The skirt 8l is supported from a reentrant portion 1Q of the wall of the bulb and makes electrical contact with 4 the metallicA deposit 2. i

through the inner end of a press v1st which is 1925. serial No. 43,221.

The anode 6, which is supported from a press 9, and surrounds the filament 3 and the grids 4. and 5, is so shaped that it co-operates w1th the imperforate cap 7 and the depending skirt 8 to prevent any light emitted by the filament4 from falling upon the inner surface of the bulb. l

The lament 3 and the grid 4 are supported from a plurality of conductors extending dlsposed coaxially of the reentrant portion '10 of the bulb.

.A photoelectric material, such as. otasslum, caesium or sodium, is applied to t e inner surface of the metallic deposit 2, preferably by distilling it'thereon from a small container (not shown), andthe material is sensitized by causing an electrical discharge to take place between the anode 6 and the grid 5 in an atmosphere of hydrogen. The resulting chemical action between the hydrogen and the potassium causes a film of potassium hydride-to be formed in a colloidal state on the potassium. The potassium hydride is highly active photoelectrically,'that is, it emits electrons under the-influence of e manner of treatment outlined above, by which a deposit of potassium `hydride is placed on the metallic deposit in a colloidal orm renders the rate at which the electrons are emitted from ten to twenty times greater ments inside the bulb 1 will vnot be shortcircuited. In'addition, the hydrogen is pumped out and replaced with an inert-gas atmosphere at a pressure that willl give maximum response of the photoelectric material. When the-tube -l'is made, a contact member 11 is placed therein for electrical connection to the Vmetallic and photoelectric deposits.

In order to describe the operation of the photoelectric cell oscillator, it will be understood that certain .electrical connections 'are' y made in themanenr shown in the drawing. 106

That is, the cathode 3 is connected through a variable resistor 12 to a battery 13. The anode 6 is connected to the filament or cathode 3 through a high-potential battery 21. The lirst gride 4 is connected through a reactance 15 to the positive terminal of the battery 21, and to one end of a reactor 17' through a condenser 24. The terminal 11 is connected through a resistor 19, battery 2O and second battery 21 to the anode 6. The resistance of the resistor 19 may be of the order of 50 megohms.

@ne terminal of the reactor 17 is connected through the grid leak 22 and grid condenser 23 to the terminal 11 and then by Way of the deposit 2 to the second gride 5. The midpoint of the reactor 17 is connected to the cathode through a contact member 18. A conductor 25 is connected through a condenser 26 and contact member 27 to the one end of the reactor 17. A. second conductor 28 is connected to the other end of the reactor 17' by Way of the contact member 29. The conductors 25 and 28 comprise the output circuit of my improved oscillator.

It Will be seen that the cathode 3, the second grid 5 and the rst gride 4 are connected in a circuit that is known as the Hartley oscillating circuit, the positive potential being applied to the grid 4 from the battery 21, causing the said grid to function as an anode. Consequently, if there is suliicient current flow from the cathode 3 tothe grid 4, an oscillating current will be delivered over the conductors 25 and 28, the frequency of which is dependent upon the constants of the 'reactor 17 and the condenser 24. The manner in which this circuit functions will appear more fully hereinafter.

It will be also seen that the negative terminal of the battery 20 is connected to the terminal 11 and that the positive pole of the battery 21 is connected to the anode 6. Inasmuch as the Voltage of the

batteries

20 and 21 are added together, a high negative potential is placed upon the metallic deposit 2 with respect to the anode 6. A lower positive potential from the battery 21 is also placed upon the grid 4.

It Will first be assumed that the photoelectric cell is dark. When the current is passed through the lilament or cathode 3, electrons are emitted from the filament. These electrons do not flow t0 the grid 4 because of the fact that there is a high negative potential existing upon the second grid 5 from the battery 20. The negative potential on the grid 5 need only be sufficient to prevent the amount of current flowing from the cathode 3 to the 'F first anode 4 to be enough to start the circuit luto oscillation. Consequently, there is no oscillating current flow in the circuit including the conductors 25 and 28. When the photoelectric cell is illuminated, the photoelectric material begins to emit electrons, the

number of which is proportional to the intensity of light. These electrons flow from the photoelectric material to anode 6 under the influence of the voltage impressed by the

batteries

20 and 21 in series.

Immediately upon the flow of current there is a voltage drop across the resistor 19, .and the voltage on the grid 5 is reduced to such an extent that the space charge is not so efective to prevent the electrons emitted from the cathode 3 reaching the grid or anode 4. The current flow in the circuit is thus increased. The voltage drop is proportional to the electron flow from the photoelectric material. This, in turn, is proportional to the intensity of light on the photoelectric cell. The voltage drop regulates the space charge which, in turn, controls the number of electrons that reach the grid 4. The electrons reaching the grid 4 thus cause the-current to flow through the circuit including the reactor 17. The amount of current is relatively high and causes the cell to break into oscillation, whereby an alternating current is supplied to the conductors 25 and 28, the amplitude of which is governed by the intensity of light falling upon the cell.

The only limit to the amount of current that may be obtained is the amount of heat radiated by the filament, which heat tends to cause the potassium to evaporate. By proper cooling arrangement, a very large current output may' be secured.

When the photoelectric cell is darkened, the photoelectric substance does not emit elec- 10o trons andthere is no current flow from the photoelectric material to the anode 6. Consequently, there is no voltage drop across the resistor 19, and a high negative potential is placed on the grid 5 which so controls the 105 space charge that no electrons from the cathode 3 reach the grid 4 or the number that do reach it are not sufcient to cause the tube to oscillate and no oscillating current is delivered to the

conductors

23 and 26.

My invention is not limited to the particular arrangement of the apparatus described, but may be variously modified Without departing from the spirit and scope thereof, as set forth in the appended claims.

I claim as my invention:

1. In an oscillatory system, a container Within which are positioned elements constituting a thermionic amplifier and a lightresponsive device, input and output circuits 120 for said amplifier, said circuits being so coupled as to promote the generation ot' oscillations, and means whereby the amplitude of said oscillations may bc controlled by said light-responsive device.

2. An oscillation generator comprising a thermionic tube having an anode, a cathode and a control-electrode, an additional electrode Within said tube capable of assuming an electric charge that will prevent the genera- 13G tion of oscillations, and photoelectric means within said tube for modifying thexcontrol exerted by said additional electrode.

3.A An oscillation generator. including a vacuum tube having three electrodes and circuits associated therewith for causing said electrodes to act respectively as cathode, anode and control electrode, means for irnpressing a blocking potential upon the control electrode and means including a photoelectric element disposedwithin said tube for removing said blocking potential.

4. In a light-responsive system, a device comprising a light-Sensitive electrode and an anode associated therewith, a thermionic cathode, a plurality of grid-electrodes asso ciated with said cathode, an output circuit associated with said device and `so arranged that oscillations tend to develop therein, one of said grids ,serving as an anode in the generation of said oscil ations, means for applying a negative blocking potential to the other of said grids, and connections within said device whereby electronic emission from said light-sensitive electrode to the anode assciated therewith renders less negative said blocking potential, whereby the amplitude of oscillations generated depends upon the light impinging on said light-sensitive electrode.

5. In a light-responsive system, a device comprising an evacuated envelope, `a thermi onic cathode, an anode'V and two grid-electrodes positioned therein, a light-sensitive substance positioned in said envelopeA and connected conductively to one of said grids, an output circuit and potential sources associated with said device and so arranged that oscillations tend to develop therein, theA other of said grids serving as an anode in the generation of oscillations, means for impressing a negative blocking-potential on said lightsensitive substance with respect to said cathode, and means includlng said first mentioned anode for rendering said blocklng potential less negative when said light sensitive substance is exposed to light.

6. In a light-responsive system, a device comprising an evacuated envelope, a thermionic cathode, an anode, and two grid-electrodes supported therein, a, light-sensitive substance positioned in said envelope and conductively connected to one of said grid-electrodes, an output circuit and potential sources associated with the other of said grids and saidvcathode and so arranged that oscillations tend to develop therem, the last mentioned grid serving as an anode inthe generation of said oscillations,fsaid sources of potential being cumulative in impressing a negative blocking potential on said light-sen#` sitive substance with respect to Said iirst mentioned anode, and means whereby the eX- posure of said light-sensitive substance to light will cause said blocking potential to become less negative.

ductive connection between said light-sensitive substance and one of said grids.

8. A composite light-sensitive cell and thermionic tube comprising, in combination, an evacuated container having mounted therein a cathode, a plurality of grid-electrodes surrounding said cathode, an anode surrounding said grid, a light-sensitive sub- 'stance deposited on a portion of the inner sury face of sa1d container, said anode and one of said grid-electrodes being so shaped andso positioned with respect to said cathode that light therefrom is prevented from reaching said light-sensitive substance. and a conductive connection between the last-mentioned grid-electrode and said light-sensitive substance.

-In testimony whereof, I have hereunto subscribed my name this first day of July, 1925. VLADIMIR K. ZWORYKIN.