US1506468A - Electron-discharge device - Google Patents

Description

Aug. 26. 1924.

W. C. WHITE ELECTRON DISCHARGE DEVICE Filed 001:. 28 1920 Fig. 2.

20 25 FLA TE VOLTAGE l5 PLATE VOLTAGE Fig. 4.

Inventor: 1 William Owhit e,

GRID VOLT/16E His Attorneg.

Patented Aug. 26, 1924.

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WILLIAM C. WHITE, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YO'RK.

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Application fil ed October 28, 1920. Serial No. 420,231.

To all whom it may concern. 4

Be it known that I, WILLIAM C. WHITE, a citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have invented certain new and useful Improvements in Electron- Discharge Devices, of which the following is a specification.

My present invention relates to electrical amplifying and radio detecting devices in which an electron current is controlled by relatively feeble voltage variations.

Two classes of radio detectors of the electron valve type have heretofore been employed.

(1) Detectors of the audion, or soft valve, type which contained enough residual gas to give the device a critical characteristic, that is, a region of instability at which the device was sensitive to radio impulses due to gas ionization.

This class of detectors were erratic in behavior. A given impressed voltage did not always produce a given effect. Tubes apparently identical in construction varied in operating characteristics and a given tube would progressively change in operating characteristics.

(2) Detectors of the pliotron, or hard valve, type in which the evacuation was so complete that gas ionization was negligible and did not afi ect the operation of the devlce.

This class of detectors although not so sensitive as the best of the first class are regular and reproducible "in operation.

In accordance with my invention, 1 have provided a soft valve detector for radio signals or the like which is fully as sensitive as the best gas detectors formerly constructed, and as regular and reliable in its operation as the vacuum detector. The detectors embodying my invention contain certain gases immune to the clean-up effect, particularly the gases of the rare or noble gas group, such as argon, helium, neon, and even nitrogen. They are steady and reproducible'in operation.

The accompanying drawing shows in Fig. 1 a radio receiving system containing a detector illustrative of the class of devices embodying my invention; Figs. 2, 3 and 4 are diagramsshowing electrical characteristics of my improved detector, and Fig. 5

illustrates a specific form of electron tube embodying myinvention.

Referring to Figs. 1 and 5 of the drawing the device here illustrated comprises an electron emitting cathode 1, consisting preferably of a tungsten filament, adapted to M heated to incandescen ce by a battery 2, or other suitable means, an anode 3, consisting of tungsten, 'molybdenum, nickel, or other suitable conductive material and a control electrode or grid 4, which in the par ticular embodiment of my invention illustrated in the drawing consists of a wire wound over supports 5, 6, and is located be tween the cathode and the anode. The anode is frequently known as the plate and the current flowing between the cathode and anode as the plate current. It is the function of the grid' to .vary the electrostatic field between the cathode and the anode, and thereby control the electron current. In the device shown in Fig. 5, the supporting and conducting wires 5, 6, 7, 8, 9, 10 and 11 are sealedinto a stem 12 of a sealed glass bulb or envelope 13, having a base 13 provided with. current-conveying terminals, only two of which are shown at 14.

As the first step to the evacuation of the device the glass bulb 13 is evacuated while being heated to at least about 360 J, in fact, as high a temperature as the glass will withstand without collapsing in order to denude the same of gas. The anode 3 also is freed from disengageable gas, preferably by electronic bombardment in a vacuum, the pump being constantly operated. For this purpose the cathode is rendered incandes cent and a voltage is applied to cause current flow between the cathode and the anode to drive out gas in the now well-understood manner. When the bulb and the electrodes have been made sufliciently gas-free, a substantially immune to clean-up is admitted, for example, a rare gas, such as argon, helium, or neon. Nitrogen may also be used although not quite so effectively.

The envelope 13 is sealed when the gas pressure is in the range of about 15 to '?5 microns, depending on the geometrical relation 01" the electrodes. In the case of the construction illustrated in Fig. 5 a pressure of about 20 to 60 microns is preferred.

The tube may be operated as detector in the usual, way in a radio system, for ex ample, as illustrated in Fig. 1. The grid 4 receives signals from the antenna 18, for example. by being connected to the secondary winding of a transformer winding 19 in series with a condenser 20. The other terminal of the secondary winding is connected to the cathode 1. An ohmic resistance 23 may be connected in shunt to the condenser 20, a switch 24 being provided to shortcircuit both the condenser and resistance. An adjustable condenser 25 may be conneoted across the transformer secondary. In circuit with the cathode 1 and the anode 3, some suitable receiving instrument. as for example, a telephone receiver 21, is connected in series with: a suitable source of.

current, for example abattery 22.

Preferably the voltage of the battery 22 in the anode or plate circuit is adjusted somewhere above ionization voltage, but materially below the voltage at which the ionization of gas in the detector becomes so intense that there is a tendency for a blue glow to form. Preferably, the operating plate voltage is about 18 to 23 volts. Under these conditions the detector exhibits amarkedly superior sensitivity to the vacuum detector of the pliotron type. In practice, the plate voltage and the filament current are varied until a maximum response is ob- 'tained in the receiver and the optimum settings thus obtained are maintained during operation over a considerable period of time. iv

Apparently this sensitivity is due to certain critical conditions of the'tube which may be explained at least in part by reference to the grid and plate characteristics, as illustrated in a conventional manner in Figs. 2, 3 and 4. In Fig. 2 I have shown plotted for illustrative purposes a representative set of readings of plate currents plottedas ordinates and plate voltages as abscissae. The currents obtained with different impressed volatges in a device evacuated so highly that the ionization of residual gas is negligible is represented by the curve 26, which over a short region, say, above about 10 to 15 volts, substantially obeys the 3/2 power law of pure electron conduction. In other words, the currents obtained with different impressed voltages vary directly with the 3/2 power of the voltage. In a tube constructed in accordrising voltages varies with a higher and ance with my invention and containingv ionizable gas, the increase of current with constantly increasing power causing the characteristic to be more steeply curved, as illustrated by the curve 27.

Related intimately to this plate circuit characteristic is the grid-voltage, plate-current characteristic as illustrated in Fig. 3. When in a given tube different steady voltages are applied to the plate circuit, and

the grid voltage is varied below and above zero, a series of corresponding plate currents are obtainable. In Fig. 3 the curve 28 represents the relation of grid voltage of a vacuum tube above and below zero to current in the plate circuit with a steadily applied plate voltage of 40/ volts. In a tube embodying my invention, the change of current obtained by varying the grid voltage with a steadily applied plate voltage of 20 volts is illustrated by the curve 29. This curve is steeper even at the lower plate voltage and not as straight as the curve 28.

The slope of the curve thus obtained is usually designated as rho. In other, words. the value of rho represents the relation of the change of current in the plate circuit. in micro-amperes to the change of voltage in the grid circuit in volts. This value is also known as the conductance of the tube and is usually expressed in microbnis.

Fig. 4 illustrates the conductance of the tube at different plate voltages. The conductances are plotted in microhms as ordinates, and the plate voltages are plotted asabscissae. It will be observed thatthe curve 30 expressing the conductance of a high vacuum or hard tube has a gentle uniform slope. On the other hand, the curve 31 expressing; the conductance of a soft'tube embodying my invention, follows very closely to the curve of the vacuum tube up to a value of about 16 volts, and then very sharply bends upward and becomes almost vertical. In other words, at and above the ionization voltage of the gas filling in the tube, the conductance of the tube varies very rapidly with different plate voltages. Inv fact, results indicate that at some voltages in a range above and in the neighborhood of the ionization the conductance varies even more abruptly than indicated b the conventional; curve shown in the di agram. When a tube embodying my invention is operated as a detector with a plate potential. above ionization voltage. say. at 18 to 23 volts. which is well below the voltage at which the ionization becomes so intense as to produce a glow. the rate of change of conductances is high andv there fore the rate of change of current in a receiver circuit is correspondingly great. As a result the device is very sensitive to feeble variations of voltage in the grid circuit, such, as for example, produced by weak radio signals.-

In the soft tubes formerly produced this condition of sensitivity was extremely variable and erratic due to the continual variation of the gas content of the tube. This variation was apparently due to the liberation of gas from the parts of the tube, particularly the bulb, and the simultaneous clean-up of gas was due to chemical and physical action within the tube. In a detector tube embodying my invention these sources of variation are removed, the bulb and working parts of the tube having been freed from disengageable gas and the gas filling being substantially immune to cleanup eflects. Whatever may be the correct explanation, the characteristics of my device are steady and reproducible, as contrasted with the unsteady and non-reproducible characteristic of soft tubes heretofore known. The device is so exceedingly sensit-ive in its operation that it is probable that the operation of the same involves phenomena not at present apprehended.

While I have described the operation of my improved detector as involving the ionization of the low pressure gaseous filling therein, I do not wish to be limited by this theory of operation as the benefits of my invention may be obtained independently of any particular theoryof operation.

What I claim as new and desire to secure by Letters Patent ofthe United States, is

1. An electron discharge device comprising a sealed container, a cathode adapted to operate at incandescence, an anode, a chargereceiving member or grid for controlling a current in said device, the container and parts of said device being substantially deprived of disengageable gas, and a filling of gas substantially immune to clean-up effects at a pressure of about 15 to 75 microns in said container.

2. An electron discharge device comprising a sealed container, a cathode adapted to emitelectrons, an anode, means for varying the electrostatic field about said electrodes,-the walls of said container and the electrodes being substantially deprived of disengageable gas, and a gas filling substantially immune to clean-up effects and non-condensible at ordinary temperatures sufiicient in amount to produce at a given voltage between said cathode and anode by a progressive change of the electrostatic field in the positive direction, a corresponding regular increase of current between said electrodes which is greater than the increase under the same conditions in a similar device in which the residual gas is negligible, said gas content being insufiicient to produce blue glow under operating conditions.

3. A radio detector comprising a sealed container, a filamentary cathode adapted to be heated to incandescence, an anode, a grid located intermediate said electrodes and a quantity of rare gas at a pressure of about 15 to 7 5 microns of mercury, said container and electrodes being deprived of disengageable gas, said device being capable of operation at voltages impressed on said electrodes above ionization voltage and below a luminosity producing voltage.

4. A radio detector comprising the comgreater than the 3/2 power-of the voltage, the pressure of said gas being insufiicient to enable an arc-like discharge to occur therein.

5. A radio detector comprising the combination of a cathode adapted to emit electrons by incandescence, an anode, a discharge controlling grid, an enclosing envelope, a filling of argon gas therein at a pressure of about 15 to 7 5 microns of mercury, a source of current having a voltage above ionization voltage but insuficient to produce a luminous discharge in said gas in circuit with said cathode and anode, the quantity of said gas filling being suficient to cause the current in said circuit to vary with variations ofvoltage over a working range at a rate materially greater than the 3/2 power of the voltage .but being insulficient to permit an arc-like discharge to occur therein atthe voltage of said source.

6. A radio detector comprising a sealed container, a cathode operable at incandescence, an anode or plate, a charge-controlling electrode or grid and a filling of gas at a pressure of about 20 to microns of mercury, said container and electrodes being deprived of gas, the conductance of said detector increasing more rapidly with rise of plate voltage above the ionization voltage of said gas filling than would be the case in said device were the residual gas at materially lower pressure.

7. A detector for radio signals comprising the combination of a sealed bulb, a cathode therein adapted to emit electrons, a plate or anode, the bulb, walls and contained members being substantially freefrom disengageable gas, a filling of attenuated gas which is substantially immune to electrical clean-up efiects, a source of current connected in circuit with said cathode and anode having a voltage above and adjacent to the ionization voltage of said gas,-the pressure of gas in said bulb being so related to the voltage of said source that the variation of conductance of said detector with variation of plate potential is materially greater than when gas Ionization is negligible.

8. A detector for radio signals com rising the combination of a sealed bul a cathode operable at incandescence, an anode anda grid therein, the parts of said device 139 being substantially free from disengageable gas, a rare or noble gas thereinat a pressure of about 15 to 75 microns of mercury, and a source of potential of about 18 to 23 volts connected between said cathode and anode.

9. An electrical discharge device comprising a container, an attenuated gas therein which is substantially immune to cleanup effects, a cathode operable at incandescence, means for heating said cathode, an anode, a control electrode, said container and electrodesbeing deprived of disengageable gas, and a source of current at a voltage of about 18 to 23 volts connected between said cathode and anode, the pressure of the gaseous filling being so chosen that the current between cathode and anode varies .more abruptly with variations of potential of the control electrode than whenthe residual gas pressure is so low that ionization effects are negli ible.

10. A radio etector apparatus comprisinga sealed container, a filamentary cathode of refractory material, an anode, a grid, said container and electrodes being deprived of gas, a filling of argon at'a pressure of about 20 to 60 microns, a source of current at a voltage of about 18 to 23 volts connects ed between said cathode and anode and mefins for impressing radio signals'on said gri In witness whereof, I have hereunto set my hand this27th day of October 1920.

WILLIAM C. WHITE.

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