US1775886A - Electron-discharge device - Google Patents

Description

p 6, 1930. R. E. H. CARPENTER 1,775,886

ELECTRON DI S CHARGE DEVIQE Filed Jan. 20. 1926 4 Sheets-Sheet 1 iga ,1 WK Jan- 7 IZWLWZ 1 iQyZ,

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R. E. H. CARPENTER p R. E; H. CARPENTER 1,775,886

ELECTRON DISCHARGE DEVICE Filed Jan. 20. 1926 4 Shoots-Sheet 3 7 ZiF/Wwfr 6% Sept. 16, 1930-.

R. E. H. CARPENTER ELECTRON DISCHARGE DEVICE Filed Jan. 20. 1926 4 Sheets-Sheet 4 -lllll jjgzz;

, v 3nveutor .R. I. .H: O'ai uenter 6L m m Gflomeg Patented Sept. 16, 1930 PATENT OFFICE RUPERT EVAN HOWARD CARPENTER, OF PURLEY, ENGLAND ELECTRON-DISCHARGE nnvrca Application fled January 20, 1928, Serial No. 82,581 and in Great Britain January 24, 1985.

so-called soft type of such devices, that is to say those in which ionization plays a material part in determining the characteristics of the device.

The primary object of this lnvention 1s to amplify or otherwise improve the negative reslstance or impedance characteristics of such electron discharge devices. Further objects will transpire hereinafter.

According to this invention an ionic charge collector of extended surface is employed, such collector being the electron controlling member or an element associated with it so disposed that there are communicated to such collector charges having a component in phase with the charges on the electron controlling member which gave rise to the change in the ionization within the tube. This invention may be stated to consist of a device comprising a cathode, an anode, a further electrode or electrodes and a medium capable of ionization at a pressure sufficient to give the device negative resistance or impedance characteristics of a type which are smoothly'and easily controllable over a wide range of values while the value of the negative resistance or impedance is suflicient- 1y low to give zero decrement to circuits having values of L, G and R commonly employed in radio circuits. Such negative impedance characteristics are in part maintained at frequencies exceeding 10 cycles per second and the apparatus when suitably adjusted will operate as a rectifier or detector of electrical oscillations applied to it, or it may be employed for the amplification of oscillations or other electrical variations. Alternatively, it may operate simultaneously as a negative impedance device and as a detector or as an amplifier or both as a detector and amplifier. Further features of the invention will be described in the following specification.

Electron discharge devices containing traces of gas or vapour suflicient in amount to affect appreciably the electrical perform? ance of the device, show under suitable conditions of adjustment, a falling grid-current grid-voltage characteristic but the numerical value expressed in ohms of the negative impedance which this falling characteristic indicates is usually much too large to be of practical utility at any rate in circuits having convenient values of L, C and R. In order to develop an appreciable slope in such grid characteristics abnormally high anode voltages have sometimes been employed. Furthermore, the development of a negative slope in the static grid characteristic, when plotted point by point by the ordinary methods of observation, is no guarantee that such a device will operate to reduce appreciably the decrement of an associated circuit tuned to the higher radio frequencies.

The desired characteristics are obtained according to the present invention by the use of an electrode or electrodes of extended surface so proportioned or disposed as to receive the charges of the positive ions formed from the contained gas or vapour by the passage of the electron discharge. Such electrode or electrodes is or are arranged so as to present a surface substantially parallel to or out of the electron stream, large compared with that in or transverse to the electron stream. This result may be attained by suitably proportioning or disposing the electrode or by both means. In some cases it is advantageous to extend such collectors of ionic charges into the zones of richest ionization.

In order to reduce as far as possible any time-lag effect that might become apparent at high frequencies, it is preferred to employ gas of small molecular weight in the' envelope although it seems probable that at the highest frequencies it is chiefly those ions formed from molecules near the collector, or possibly in contact with it, which are usefully engaged in the operation of the device. On account, therefore, of its low molecular weight and well known stability of pressure at moderate potentials, it is preferable to employ helium as the medium through which the electron discharge passes although other gases or vapours may be used.

I so

call Experiments have shown, however, that on comparing two electron discharge devices of similar construction and dimensions one filled with a mixture containin about 95% helium and 5% neon with possi ly traces of other gases and the other containing approxlmately 80% neon and 20% helium with possibly traces of impurities and adjustmg the devlces for equal negative impedances at a frequency of 10 cycles that the static characteristic of the neon filled device was more than twice as steep as that of the helium filled device. That is to say, the performance. at 10 cycles of the device containing chiefly neon had fallen ofi much more from its static characteristic than had that of the device containing chiefly helium. The anode'voltages employed during the experiments were the same and the radio-frequency impedances were adjusted by controlling the filament currents. The total pressure in the helium filled tube was greater than that in the neon filled tube. It is assumed that the ratio of charge to mass for most of'the ions taking a useful part in the production of the radio-frequency negative impedance slope, is smaller in the case'of the valve containing chiefly neon than in the case of that containing chiefly'helium. It should be noted,

however, that further investigation may modify this theory. It is possible that in taking the static characteristics, the emission from the filament is influenced frompoint to point b differences produced by its 1onic or molecu ar bombardment by molecules of different mass and velocity.

Several embodiments of the invention will now be described with reference to the accompanying drawings in which Figures 1 and 2 represent diagrammatia cross section and elevation respective y of one form of construction. Figures 3 and 4 show series of characteristic curves for a device constructed in accordance with Figures 1 and 2.

Figures 5, 6 and 7 illustrate modified forms of construction.

Figure 8 illustrates a radio circuitincorporating the invention.

Fig. 9 is an elevational view of a complete valve employing the construction of F i' 7.

Figure 10 illustrates a form of the invention in which the grid is composed of flat plates; v v

Figure 11 is a vertical sectional view of the form of the invention shown in Fi an external coil adapted to estabhsha magnetic field within the tube; and

Figure 12 illustrates a further modified form of the invention in which the ion pickup electrode and the anode consist of helical str'ps interspaced and coiled progressively side by side. 2

Referring to Figures 1 and 2, the anode 1 'is cylindrical and is carried by the support 2.

and it will be noted ably better 6 having trode surface of very large area which it will.

be seen is substantially parallel with the adjacent electron stream emitted by the cathode.

The family of static characteristic curves shown in Figure 3 illustrates the variation of anode and grid current with variation of grid voltage with various values of anode voltage, namely, 105, 100, 95, 90 and 85 volts, respectively. While these curves are of interest in giving information concerning the performance of the device in low frequency apphcations, it must not be assumed that they will hold at radio-frequencies and where it is desired to ascertain the quantitative performance at such frequencles'it is essential to make a measurement ofthe ance'at the frequency at which the device is negative imped- I desired-to operate. For this purpose'a circuit consisting of parallel inductance and capacity with means for adjusting the total effective resistance gfthe oscillating circuit so formed, ma y be connected between grid and grid battery or potentiometer'or between the grid and the negative filament terminal and the resistancein the tuned circuit varied until oscillations therein are onl just sustained. The total effective values of C and R with the filament switched off in the tuned circuit, are now ascertained and the value of L/CR may be taken as a measurement of the negative impedance of the device at the tuned frequency. Measurements give a value at 10 cycles, for the device whose characteristics are illustrated, of approximately minus'37300 ohms for the conditions Ea= volts, Ef=4.3 volts, Eg=0 volts that this value diverges widely from thefigures calculated from the static characteristic.

However, with other adjustment considernegative impedance values than the above can be obtained. Thus with Ea=l10 volts, Ef=4.9 voltsand Eg=0 volts a negative impedance of 18800 ohms was measured at 10 cycles.

By careful adjustment, frequencies have been generated of'the order 10 cycles er troactive effects due to the inductance of the.

leads of the anode circuit.-

flat or curved.

of the well known ways. Where in order to secure improved amplification or detection it is desired to adjust the device electrically to a point where the negative input impedance is so low that sustained oscillatlons -would be set up, negative or reversed retroaction may be used either to control the amplitude of such oscillation or to suppress it.

The closeness of approach to oscillation may be controlledb' varying the elfective ositive resistance 0 the oscillatory circuit y means for example of a variable condenser in series with a resistanceshunted across the oscillatory circuit.

In some cases the telephones or other detecting device may be included in the'grid circuit in series with-the radio frequency circuit and in this case enhanced selectivity 'to a particular audio-frequency can be obtained by the choice of suitable constants for the telephones and if desired by the useof an adjustable condenser in parallel with them since in this case the negative input impedance of the device will operate to reduce decrement both of the radio-frequency circuit and of the telephone circuit at their appropriate frequencies.

In the modification illustrated in Fi advantage is taken of the magnetic the filament current and the extended third electrode surface is provided by the arrangement of a series of conical plates or discs 7 carried by the, support 8. The dotted line r 9 in this figure indicates the general direction of motion ofan electron towards the anode,

while the dotted line 10 indicates the general direction of travel of a positive ion towards the collecting surface of the third electrode or grid. In a modified form the discs may be When magnetic fields are employed to modify the paths of the positive ions and negative charges, these fields may be produced by a coil surrounding the tube and energized from a source external to the envelope. A form of third electrode suitable for use with an axial magnetic field is illustrated in Figures 6 and 11, in which the vanes or blades 11 are curved to conform with the modified paths indicated by lines 9 and 10. Figure 11 also shows the magnetizing coil surrounding the tube to serve as a means for establishing a magnetic field.

In some cases, an electrode distinct from eld' of the grid proper is incorporated in the electron discharge device and is arranged and disposed to collect the charges of positive ions for lmposing on the grid. This electrode and the grid are electrically associated by being directly connected within or without the envelope, or b an other type of electrical coupling whic wi l serve to impress on the grid, potentials corresponding with the pickup of positive ions and conduction of the charges thereof by the other electrode.

In this modification, therefore, there are two associated electrodes, the one adapted primarily to control the electron flow from cathode to anode and the other primarily to pick up the charges of positive ions. These two associated electrodes may lead to a common terminal as in Figure 7 or to separate terminals as in Figure 12. In the latter case instead of directly connecting the two terminals by an electrical conductor, a potential difierence may be impressed thereon or they may be connected respectively in circuits which are inductively coupled together as indicated in Figure 12.

In such cases it is generally contemplated to dispose the ion-pick-up electrode or collector out of the electron path between cathode and anode. In one arrangement the ionpic'k-up electrode is interspaced with the anode, that is to say, the electrode occup ing spaces in the anode, as for example two helical strips coiled progressively side by side as shown in Figure 12. In another arrangement illustrated in Figure 7, the anode 12 consists of a cylindrical coil surrounding the third electrode. or grid 13 disposed symmetrically about the cathode 4. The fourth or ion-plck-up electrode 14 consists of a cylinder surrounding the anode. In this case the electrodes 13 and 14 are connected together within the envelope of the discharge device.

The diagram of Figure 8, which shows an electron discharge device 15 constructed in accordance with this invention, connected in a radio circuit, is self explanatory.

During manufacture the device may be treated as though a hard vacuum were to be obtained by the usual methods for the removal of occluded gases, and subsequently the purified gas, in this case helium, should be admitted to the envelope and adjusted to the desired pressure suflicient to give the tube a pronounced negative resistance characteristic in the grid circuit by the flow-of current resulting from the collection of positive ions upon the said large area of the control electrode. The most suitable pressure will vary somewhat according to the purpose for which the device is required and according to the design and proportions of the parts. The pressure may be determined experimentally provided that sufiicient precautions are taken to exclude oxygen and other impurities tending to interfere with emission,

by ascertaining the dynamic or static characteristics of the devices while they are connected to the pumping system. .It was found that the pressure of a mixture consisting of 95% helium and 5% neon of the order of 0.6

millimeter of mercury gave'satisfactory results in receiving valves of the dimensions indicated in Figures 1 and 2. It is well known that the number of collisions between electrons and molecules in an electron discharge device depends on the ratio of the distance between cathode and anode and the mean free path of an electron amongst the molecules. Further, it is known that the number of such collisions resulting in ionization of the gas or vapour varies considerably for different media. It follows that the amount of ionization depends largely on the distance between cathode and anode and the pressure and characteristics of the medium. and of course the operating voltage. Strong ionization efiects are needed in the present device and it is desirable to employ such a pressure that the number of ions being produced is an appreciable percentageof the number of electrons producing them; the presence of too little gas necessitates an unduly high anode voltage in order to obtain satisfactory negative resistance values, or may make it impossible to produce satisfactory values: in any circumstances, whereas too much gas makes it impossible to raise the anode voltage high enough to give satisfactory dynamic negative resistance values without producing discontinuities in the characteristic curve. in some cases the valves have to be subjected to a subsequent ageing process, possibly for the removal of traces of impurities. It would appear, however, that if sufficient precaution is taken to exclude impurities, the ageing process may be dispensed with at least in the case of some gases. Where gases which are chemically inert with respect to the filament are used as the media to'beionized, getters may be employed.

' The static characteristics shown in Figure 3 of a device constructed according to Figures 1 and 2, and treated as described above, are substantially the same over the ranges shown whichever way the grid voltage is varied, the curves being free from discontinuities and loops. This, in conjunction with the variation in negative resistance input characteristic with different filament heats shown in Figure 4, is of great advantage in the control, for example, of a tuned circuit intended for the reception of telephony, since with suitable values of anode and grid potentialand the latter may be zero, positive or negative to the negative end of the filamentP-it is possible to give the associated circuit any desired value of decrement from that determined by its positive resistance down to zero.

In the case of discharge devices having negative resistance characteristics in which loops occur it will be appreciated that this smooth control of decrement is not possible in the range covered by the loops and if they are present there is always the danger that an atmospheric or a variation in the battery voltage may cause the apparatus to flop around such a loop, necessitating its resetting. Moreover, where such devices are used for the generation of oscillations, it is clear that the amplitude of such oscillations must at least be equal to the voltage width of the loop and that anything causing the amplitude to decrease below this value will cause a cessation of the oscillation. It may .further be remarked that where such loops exist, a specially high ratio of L to C is generally necessary forthe production of oscillations.

However, loops in the characteristic may not be objectionable if the working part of the characteristic is well removed from them, and if the curve repeats without loops over the working range.

When this invention is to be used for generating oscillations, the mean otential oii the grid or ion collecting mem er may be made considerably more negative than any of those. values of grid voltage which give a negative slope to the grid current curve or indeed any grid current at all. In this condition it will, in some cases, be necessary to start the oscillation by means, for example, of an external electrical impulse applied to theinductance of the oscillating circuit. The adjustment of the apparatus in this wa with the grid so negative that normally no current flows through the valve, will in many cases give an enhanced eificiency to the device as agenerator of oscillations, but in this state the device is not capable of giving the smooth control'of decrement from that normal to the circuit down to zero, that it can give when the grid is at or about the same potential as the negative end of the filament.

I claim:

1. An electron discharge tube comprisingin combination an envelope, an electron emitting cathode, and an anode mounted therein, a control electrode having a relatively large area which can collect positive ions and a relatively small area subject to direct electron bombardment, and a gaseous filling within said envelope, capable of being ionized by collision and at a pressure suflicient to give the tube a pronounced negative resistance characteristic in the grid circuit by the flow of current resulting from the collection of positive ions upon the said large area of the control electrode.

'2. An electron discharge tube as defined in claim 1 and wherein the gas is at a pressureof a substantial fraction of a millimeter of mercury. I

3. An electron discharge tube comprising in combination an envelope, an electron emitting cathode, and an anode mounted therein, a control electrode conslstlng of a plurality of plates located between the cathode and stream and present a relatively large area i for attracting and collectingpositive ions from the ionized as thereb to reduce a pronounced negative resistance characteristic in the grid circuit. v

4. An electron discharge tube as defined in claim 1 and. wherein saidgaseous. filling consists mainly of helium gas. a An electron discharge tube comprising in combination an envelope, a linear electron emitting cathode, means for establishing a magnetic field substantially parallel to said cathode to modify the paths of the electron flow from said cathode, a control electrode consisting of a plurality of plates conforming with the modified electron paths'and a gasoous filling capable of being ionized by collision and at a pressure-of approximately 0.6 millimeter of mercury.

RUPERT EVAN HOWARD CARPENTER.

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