US2098217A - Electronic apparatus - Google Patents

Description

Nov. 9, 1937. F B. AUBERT ET A. 2,098,217

ELECTRONIC APPARATUS Filed Aug. 22, 1935 v 2 Sheets-Sheet l mm W 1937- F. B. AUBERT ET AL ELECTRONIC APPARATUS 2 Sheets-Sheet 2 Filed Aug. 22, 1935 30 properties of Patented Nov. 9, 1937 UNITED STATES PATENT orrlcs 2,098,;17 moraomc arraaa'rus tlon of Illinols\ Application August 22, 1935, Serial No. 37,390

l'lclaims. -(o1.zo--41.s)

The present invention relates to electronic apparatus. 7

The principal object of the invention is to provide improved electronic apparatus which is re- 5 sponsive to light.

Another object of the invention is to provide improved electronic apparatus wherein a single electron tube serves both as a light-sensitive device and as an amplifying device.

' Another object of the invention is to provide improved electronic apparatus serving as an amplifier.

Our invention is based on an improved relation of circuits and the establishment of certain approximate conditions in association with an electron tube, whereby the tube is caused to operate in a manner, and with attendant phenomena, which, so far as we know, have not heretofore been known. As one illustration of this phenomena, by the practice of our invention we are enabled to make a typical three-element amplifying tube responsive to light. Such a tube, of the high vacuum type, constructed primarily for amplifying purposes, has no photosensitive coating of caesium, sodium, or the like on the plate (anode) in the original manufacture of the tube. Nevertheless, such a tube, operated according to our invention, is made highly sensitive to light, exhibiting many of the the conventional phototube or photo-electric cell,, and, in addition, affording a greater stability of operation, greater reliability,

and a longer life, than are attainable with the v conventional phototube. Furthermore, the use of such a three-element tube appears to cause the control grid to function inan amplifying capacity so that the range of current variation in response to light variation is in a much larger ratio than is obtainable from a conventional phototube. Y

Other objects, features and advantages of our invention will appear from the following detailed description of certain preferred embodiments thereof.

In the accompanying drawings,

these embodiments and illustrating a hypothesis of operation:

Figures 1, 2, and 3 are diagrammatic illustrations of diiferent embodiments of our invention functioning as light-sensitive apparatus, and emplcying a single tube;

Figures 4 5, 6, and 7 are diagrammatic illustrations of other embodiments utilizing the fundamental circuit arrangements of our invention for amplifying purposes; and

, priate point.

illustratin Figure 8 is a diagrammatic illustration of another embodiment using direct current in the grid circuit. i

We shall first describe the invention in an alternating current adaptation, wherein the plate 5 circuit is energized by an alternating current. Referring first to Figure 1, the tube'2l is a standard three-element tube of the high vacuum type, commercially referred to as an R. C. A. Radiotron or Cunningham Type 71A". Such' tube com- 10 prises a filament or cathode 22, a control grid 23, and a plate or anode 24. In the alternating current adaptation of the invention the source of power supply is any 110-volt, 60-cycle lighting circuit represented by the conductors 25, 28 con- 15 necting with the primary winding 29 of the power transformer 28. In this embodiment the plate circuit or work circuit of the tube is supplied directly from the lighting circuit 25, 26, this plate circuit comprising the conductor 24a leading 20 from the plate 24 and connecting with the responsive device 3|, the conductor 24b leading 'from the responsive device to one side 26 of the supply circuit, and the conductor 240 leading from the other side 25 of the supplycircuit to 25 the filament circuit 22a, 22b connecting with the filament winding 220. The actuated device 3| is shown as a relay adapted to open and close one or more secondary circuits, the winding of this v relay being shunted by a condenser 32. For 30 maximum sensitivity when using a ll-A tube, the relay is preferably between 3000 and 5000 ohms and the condenser is preferably between 2 and 4 microfarads, the sensitivity being materially influenced by proper choice of values in this part of 35 the circuit. Other values may be desirable for other tubes. Reference willhereinafterbemadeto the plate current flow as given by a milliammeter 33 interposed in the plate circuit at any appro- 40 The circuit for the filament 22 is represented by the conductors 22a and 22b connecting with the secondary winding 220 of the transformer 28.

The conductor 24c of the plate circuit can be connected to either end or to a mid-point of the 5 secondary winding 220. The filament is energized with its standard rated voltage and current, which is approximately 5 volts and .25 ampere.

The control exercised over the grid 23 is infiuenced in part by certain connections which, 50 for brevity, we shall refer to as a grid circuit, although these connections may not establish a complete electrical circuit in the common conception of that term. This so-called grid circuit comprises a conductor 2341 leading from the grid with ground at an, although connection with a trueground"isnotemential,aswillhereinaiter appear.

'lhe apparatus is most sensitive to ahli when the potential set up in the secondary winding 234 oi the grid circuit is relatively high, and preferably higher than the plate voltage. no: example, with a potential of 110 volts impressed ontheplate,thebestresultshavebeensecured when a potential of approximately 550 volts is establishedinthegridcircuit. Usingthetypeoi tube referred to, and the above ratio of approxi- .mately5to1betweenthegridandplatepotentials, best results have been obtained when the upper condenser 3' is adjustable in capacity between .002 and .000006 microiarad. In this same relation,- the lower condenser 80 may be either a fixed condenser or a variable condenser, best results being secured when the capacity is in the neigborhood of .002 and .00025 micro- Fcrplacingtheapparatusinconditiontow spondtolight,thesystemisfirstadiustedtoa stand-by condition in the absence of light, or with minimum l t incident upon the tube, this adjustment preferably being performed by adlusting the upper condenser II. Increasing the capacity of this adjustable condenser reduces the plate current fiow in effecting this stand-by adiustment, and, conversely, reducing the capacity of this condenserincreases plate current flow. A typical stand-by condition is with a plate current fiow of approximately 5'miiliamperes, as read on the milliammeter 33 included directly in the plate circuit. Lightisnowcausedtoialluponthe tube. 'lhis may be daylight, or it may be artificial light, such as that from any ordinary electric light bulb. The experiments conducted by us to date and our present hypothesis of the operation lead us to believe that it is desirable, if not essential, thatthelighti'allupontheinnersurtaceoithe plate 24, i. e., upon that surface of the plate which is subjected to the bombardment oi! the electrons from the filament. In the above type of tube, the plate completely surrounds the filamentandthe grldonallsidesbutisopenattop andbottom. 'Whenmingthistube,thelightis causedtoenterthetopotthetubesoastopass down through the filament and the grid and to ialluponaninnersuriaceorsurfacesoithe plate, approximately as indicated by the dashand-dot lines in Figure 1. Immediately that light is thus incident upon the tube, the plate current varies. When the apparatus is operated in the relation described above of Figure 1, the presence of light reduces the fiow of plate current. By subjecting the tube to a suilicient intensity 01' light the plate current can be reduced from its standbyvalueoi5milliamperacompletelydowntoa aero reading on the miliiammeter 38, such indicating either a complete cessation of plate current flow or the reductiontha-eotto avalue not capable 0! being read upm such an instrument.

Exploring operations conducted with an ordinary60wattlightbulb,eitherwithorwithout anapproprlatelensiorconccntratingtberays.

give results which indicate that the responsiveness of the device to light is dependant upon light striking the inner surfs-cm oi the plate. The above type of tube has the upper ends 0! the filament and grid supported by a thin supporting plate or cap of insulating material, which is provided with an oblong opening therein. When the light is caused to pass straight down through this opening so that practically no light, or a minimum amount of light, falls directly upon the inner surfaces of the plate, the variation of plate current fiow is barely perceptible on a milliammeter, except when the light is of relatively high intensity, as for example, when the bulb and lens are held just a few inches from the top of the tube. Under the latter circumstances, it is possible that there is some appreciable amount of light reflected oi! the surfaces of the filament and grid wires laterally on to the plate. The rays which are being caused to pass axially into the tube i'all directly on the-filament and grid and intersect the paths of the electrons flowing from the filament to the plate, but the lack of any substantial response to the light rays at this time indicates that it is not the action of the light striking the filament and/or grid that gives rise to the photo-sensitive action of the apparatus. Astheraysarecausedtotakemoreofalateral angle through the oblong opening they fall upon the inner surfaces of the plate, and thereupon there isan immediate diminution in the plate current fiow. When the inclined beam of light is in. a plane parallel to the greater dimension of the oblong opening there is a greater diminution of plate current than when it is in a plane parallel to the shorter dimension of said opening. This is apparently merely a quantitative variation 7 resulting from the rays being incident upon a greater area of the plate when projected through the long dimension of the opening. Daylight and sunlight result in the same response when caused to fall upon the inner surfaces of the plate, and, as above stated, when the light is of sufilcient intensity the plate current flow can be reduced from as much as 5 milliamperes down to approximately zero flow.

The apparatus appears to respond instantly to the application of light, at least human eye observations of the milliammeter deflections and of grid-plate potentials are substantially in the ratio of 5 to 1, i. e., 550 volts in the grid circuit and volts in the plate circuit. Increasing the potential in the grid circuit to 600 volts and 700 volts, etc., while retaining the plate potential at its original value of 110 volts does not increase the responsiveness of the apparatus in proportion. Conversely, decreasing the grid potential while retaining the plate potential at its 110 volts value decreases the responsiveness of the apparatus, until a grid potential is reached in the neighborhood of or 200 volts when the apparatus shows no sensible response to light. It will be understood that-we have given the above ratios and potentials for illustrating thepractical applications of our invention to those skilled in the art, but we do not mean to limit our invention thereto, since other tubes now in existence or to be hereafter produced will probably have different constants and different struc-. tural characteristics calling for different ratios and different potentials for producing the same general results.

The apparatus is most responsive when the conductor 24b of the plate circuit is connected to the ungrounded side of thelighting circuit 25, 26. The secondary winding 23d is so connected in the grid circuit that the end 230 of said winding will impress negative polarity on the conductor 23b of the grid circuit during the same alternation that the supply circuit 25, 26 is impressing positive polarity on the plate 24. The notations 5" and F are conventional transformer designations indicating the start and finish of the windings 23d and 29, and Figure 1 shows their proper connection for the above described relation. A reversal of the connections to the secondary winding 23d results in a plate current fiow which is a maximum in relation to the impressed plate voltage; for example, ap-

proximately 10 milliamperes at volts plate potential. Adjustment of the condenser 35 manifests no controlling influence at this time, and the tube is not responsive to light.

Figure 2 illustrates a modified arrangement in which the plate circuit-receives its potential from a secondary winding 24d on the transformer 28, instead of directly from the supply circuit 25, 26. The connection of the secondary windings 23d and 24d in the grid and plate circuits is such that the winding 23d impresses negative polarity on the conductor 23b substantially at the same instant that the winding 24d'impresses positive polarity on the plate 24, i. e., there is substantially degrees difference in phase between the potentials impressed by these secondary windings on the side 35b of the adjustable condenser 35 and on the plate 24. The conductor 240 of the plate circuit is connected to ground at 23h. In this embodiment, the potential developed in the grid circuit secondary 23d is preferably from three to six times the potential developed in the plate circuit secondary 24d, the aforementioned ratio of approximately 5 to 1 causing the apparatus to exhibit substantially the same degree of light sensitivity referred to above in connection with Figure 1. That is to say, assuming an arbitrary stand-by condition with a flow of approximately 5 milliamperes through the plate circuit, the subjection of the tube to a sufllcient intensity of light, incident upon the inner surfaces of the plate, causes the plate current fiow to diminish to approximately zero value.

Figure 3 illustrates a further modified arrangement, in which three separate transformers 28a, 28b, and 28c are employed for energizing each of the three tube circuits. Here again, for best performance, the ratio of grid voltage to plate voltage is preferably substantially 5 to l. The secondaries of the transformers 28b and 280 are so connected in the grid and plate circuits that the potentials impressed on the side 35b of the adjustable condenser 35 and on the plate 24 are substantially 180 degrees out of phase. The conductor 240 of the plate circuit is connected to ground 23h. This embodiment is also operable to cause a stand-by plate current fiow of approximately 5 milliamperes to be reduced to zero value when sufllcient light is caused to fall on the plate oi the tube. The employment of three separate transformers for assuring complete absence of inductive coupling between the tube circults in such embodiment, demonstrates that the phenomena of the apparatus in being responsive to light is not predicated on any mutual coupling between the tube circuits.

As previously stated, it is also an object of our invention to provide improved electronic apparatus serving as an amplifier. Figures 1, 2, and 3 exemplify three fundamental circuit arrangements, either one of which can also be used in an amplifying capacity. Figures 4, 5, 6, and 7 show the fundamental circuit of Figure 1 connected in amplifying relation to another tube designated 4i in Figures 4 and 5. For clarity of description, we shall refer to. the tube 4| as a pilot tube. The results attained in the operation of either of these amplifying embodiments of our invention afford helpful data in arriving at a theory of operation, and accordingly these amplifying embodiments will be described before proceeding to advance our theory of operation.

In Figure 4, the pilot tube 41 is also a typical three-element amplifying tube, such as a '71--A". The grid 43 of. such tube is connected through conductor 45 with the grid 23 of the tube 2|. The plate 44 of the pilot tube is connected through conductor 46' with ground at 41. In this amplifying situation, the pilot tube 4i is made the light sensitive element, the tube 2| remaining permanently shielded from light. In this arrangement, the pilot tube can be operated in a cold state, i. e., its filament 42 need not be heated. Assuming that the fundamental circuit arrangement of the tube 2| has been adjusted to a stand-by condition where a plate current of approximately 5 milliamperes is passing through this tube with little or no light incident upon the pilot tube 4 I, this plate current fiow will diminish as light is caused to fall on the inner surfaces of the plate 44 of the pilot tube. Increasing the intensity of the light falling upon the pilot tube is effective to reduce the plate current flow of the tube 2| substantially to zero. Particular attention is directed to the fact that when the grid of the pilot tube is connected to the gridof the amplifying tube, the plate current is caused to diminish with increasing light on the pilot tube, this direction of plate current change corresponding to that occurring inthe embodiments above described.

Figure 5 illustrates a-reversed arrangement in which a reverse operation occurs. In this instance, it is the plate 44 of the pilot tube that is connected through conductor 45 with the grid 23 of the amplifying tube, and it is the grid 43 of the pilot tube that is connected through conductor 46 with ground at 41, the filament 42 remaining cold as in Figure 4. The operating characteristics of this embodiment are substantially the direct reverse of the operating characteristics of the embodiment of Figure 4. with substantially the same stand-by conditions established in the fundamental circuit arrangement of the amplifying tube, light falling upon the plate 44 of the pilot tube causes the plate current fiow through the amplifying tube to increase instead of decrease. The degree of change is substantially the same in both cases, except that it is in opposite directions.

Figures 6 and 7 illustrate two other embodiments of our invention using photoelectric cells II as the pilot tubes. These photoelectric cells or phototubes may be of any conventional construction, either of thevacuum type or of the gas filled type. These tubes usually consist of two electrodes, namely, the anode II and the photo-sensitive cathode 54. The light-receiving surface of the cathode I! is usually coated with a layer of alkaline metal, such as caesium or potassium.

Referring to Figure 6, the anode I of the phototube is shown connected through the conductorliwiththegrid II of thetube 2|,andthe cathode of the phototube is connected through the conductor ll with ground at 41. The tube 2|, now functioning as an amplifying tube, is connected in the same fundamental circuit arrangement illustrated in Figure 1. Assuming that a stand-by condition with a desired current flowing through ,the plate circuit of thesmplifying tube is established, the subjection of the phototube ii to light, (amplifying tube 2| meanwhile remaining shielded from light), first causes the plate current fiow to diminish a slight amount and thereafter to increase. That is to say, assuming light of gradually increasing intensity to be projected into the phototube, the first reaction in the plate circuit of the amplifying tube is .when first subjected to relatively feeble light intensity.

Referring now to Figure 7, in this embodiment the phototube is connected in reversed relation, i. e., the photo-sensitive cathode N is connectedthrough conductor 45 with the grid of the tube 2| and the anode 53 is connected through conductor 46 with ground at 41. In this embodiment, when the phototube is subjected to light a continuous rise of current flow results in the plate circuit of the amplifying tube. This action is somewhat comparable to the action occurring in the embodiment of Figure 5.

In each of the amplifying embodiments illustrated in Figures 4, 5, 6, and '1, the fundamental circuit arrangements of Figures 2 and 3 can be used in conjunction with the tube 2|, in lieu of the fundamentalcircuit arrangement of Figure 1,

with substantially the same results in each case. In each of the embodiments of Figures 1 to '1, inclusive, alternating current is used in the plate circuit and the grid circuit, such being the preferred manner of operating our apparatus. The apparatus is also operable when using direct current, particularly in the grid circuit. Referring to Figure 8, this embodiment is the same as Figure 1, except that a battery or other source of direct current 58 is connected in the grid circuit in lmu of the secondary winding 23d. To obtain the desired light sensitivity of the tube 2i, the voltage of this battery must be relatively high. Approximately the same aforementioned ratio of to 1 between grid circuit voltage and plate circuit voltage gives satisfactory results, altho a lower ratio can be used where a relatively high degree of sensitivity is not desired. It is significant that forsatisfactory results the negative terminal of said battery 58 should be connected to conductor 23b for making the plate 35b of the variable condenser ll negative. This would state of balance for rendering the tube sensitive to light. A battery or other source of direct cur-- rent can also be interposed in the grid circuits of Figures 2 and 3 to take the place of the transformer windings lid with satisfactory results in each instance; and, correspondingly, these embodiments of the apparatus can be utilized in the amplifying arrangements of Figures 4 to 7, inclusive. -.'I'he filament or cathode 23 can be energized by; direct current if desired, and irrespective of the current used the cathode'can be of the directly or indirectly heated type, as desired.

In the preceding description we have referred to the tubes 2| and ll as being of the type com moniy designated as 71A. Our specific reference to this tube is solely for the purpose of giving definite values in changes of light current flow under certain operating conditions. Experimental tests show that the present invention is not limited to the use of this specific tube functioning in the capacity of the tubes 2| or II of our disclosure, since numerous other tubes of this same general class give corresponding results in the same fundamental circuit arrangements of Figures 1 to 7, inclusive, although possibly difi'erent values in change of plate current flow, etc.

Our proposed theory of operation, which appears to be completely supported by experimental results obtained from the embodiment of Figures 1 to 8, inclusive, is: (1) that a coating of lightsensitive material is transferred from the cathode and is deposited on the plate 24 during the use of the tube; (2) that when this light sensitive coating on the plate is subjected to light it results in an electronic emission from the plate, particularly when the plate is negative. The first hypothesis that a coating of light-sensitive material is deposited on the inner surfaces of the plate 24 with continued use of the tube appears to be definitely substantiated by experimental proofs. As originally constructed, the plate of a 71A tube has no coating of light-sensitive material thereon. The cathode of such a tube is of the directly heated type wherein the electrons passing to the plate areemitted directly from the filamentary wire, and this filament is coated with an alkaline-earth, such as an alkaline-earth oxide, which material is photo-sensitive to a marked degree, i. e., it emits electrons in the presence of light. Upon the assembly of these tubes in the factory, they are all subjected to a relatively brief testing operation before shipment. Experimental results indicate that this brief testing operation results in a limited amount of the filamentary coating being carried over from the filament to the plate along with or as a part of the flow of electrons and being deposited on the plate; and that continued operation of the tube over a longer period of time increases the amount of photosensitive material which is carried over to the plate and deposited thereon. The difference in results obtained when .first using a brand new tube secured directly in Figures 1, 2, 3, and 8, or the tube 2| or 4| in Figures 4, 5, 6, and 7, except that such new tube does not have as much sensitivity or responsiveness as has been pointed out above. However, by subjecting the tube to a certain conditioning operation which we have developed for the purpose, the sensitivity or response of the tube can be greatly increased. This conditioning operation is that of producing an electronic flow from the filament to the plate for a substantial time interval, say for one or two hours or more. The filament is heated with its rated current fiow, and the rated positive potential is impressed on the plate, the grid meanwhile being retained neutral or preferably positive for securing a maximum electronic discharge from the filament to the plate. The plate potential at this time is preferably direct current, although alternating current can be used, the latter merely necessitating a longer conditioning period. The conditioning interval can be shortened by utilizing a higher plate potential, or a higher filament current, or both, but this introduces the possibility of injuring the tube. It would appear that this conditioning operation results in a greater amount of the light-sensitive filamentary coating being carried over to the plate and deposited thereon, because after such conditioning operation the sensitivity of the tube is increased to a marked degree.

The other hypotheses that this coating of light sensitive material on the plate emits electrons in the presence of light, and that these electrons enable positive charges to be dissipated from the grid, appear to be supported by the results obtained in the embodiments of Figures 4 and 5. Referring to Figure 4, the fact that when light is projected on the plate 44 of tube 4| (a conventional three-element tube with the filament in a cold state) there is an immediate diminution of plate current flow through tube 2| would indicate that grid 23 of tube 2| has been placed in a less positive or more negative condition. Positive charges have apparently been dissipated from this grid over conductor 45 to grid 43, and thence over the stream of electrons to the plate 44 and through conductor 46 to ground. These positive charges apparently fiow in a direction opposite to the direction of fiow of the electrons, similarly to the commonly accepted sense of a current flow in a direction opposite to the flow of the electrons. Referring to Figure 5, the fact that the plate current flow through'tube 2| increases as light is projected on tube 4| would indicate that the grid 23 of tube 2| is caused to acquire a more positive or less negative condition. This would indicate that positive charges are conducted from ground 41 through conductor 46 to grid 43, and thence over the stream of electrons to plate 44, in a direction counter to the flow of electrons, and. through conductor 45 to grid 23. Both of these embodiments demonstrate a photosensitive property in the tube 4|, and the opposite results obtained by reversing the connection of this tube in the circuit would indicate that there is an electronic emission from the plate 44 of said tube in the presence of light.

In Figure 6, the fact that the plate current flow through tube 2| first diminishes when relatively feeble light is projected on the phototube 5| indicates that positive charges are being conducted from grid 23 through the photo-tube 5| to ground at 41. The fact that the plate current flow rises when a greater intensity of light falls upon the photo-tube 5| indicates that there is a plate-grid current flow from plate 24 to grid 23 and thence through photo-tube 5|, which plate-grid current flow renders the grid 23 more positive or less negative.

Referring to Figure 7, the fact that the plate current fiow through tube 2| rises from the time minimum light falls on the photo-tube 5| until maximum light falls thereon indicates that there isv a conduction of positive charges from ground 41 through the photo-tube to the grid 23.

The following theory is advanced as a basis for explaining the novel functioning of the tube 2| in controlling the current flow in the load circuit in response to change in intensity of light either on the plate 24 itself or on the "pilot tubes 4| and 5|. It will be understood that this description is not to be considered as limiting our invention in any way but rather it is to be considered merely as a means for more clearly understanding it.

Considering first the circuit arrangements 11- lustrated in Figures 1, 2, and 3 of the drawings, it will be recalled that the potentials of the grid 23 and the plate 24 are opposed to each other. That is, at the instant when a positive potential is applied to the plate 24, a negative potential is applied to the grid 23, both of these potentials being relative to the filament or cathode 22. Since the windings 23d and 24d, Figure 2, are connected in additative circuit relation they may be considered as being a single winding of a transformer one terminal of which is connected through the load circuit including the relay 3| to the plate 24 while the other terminal is connected through the condenser 35 to the grid 23. A tap is taken off of this winding at an appropriate position intermediate the terminals and is connected to ground or at least it is connected to the cathode 22. Thus, during the half-cycle of the alternating current when a positive potential under these conditions is applied to the plate 24, a negative potential is applied to the grid 23. During this half-cycle the tube 2| is conducting to an extent which is determined by the potential of the grid 23 with respect to the cathode 22. That is, the more negative that the grid is with respect to the cathode 22 during this halfcycle the less current will be conducted through the tube since a smaller number of electrons will be permitted to leave the heated cathode 22 for bombarding the plate 24. It will then be obcurrent the grid 23 becomes positive with respect to the cathode 22 while the plate 24 becomes negative. Since current is conducted only during the time when the plate 24 is positive, no current will be conducted by the tube 2| at this time. However, electrons will bombard the grid 23 during this half-cycle since it is positive relative to the cathode 22. As a result a negative charge will be acquired thereby, which to a certain extent, will leak of! through the grid circuit and through the various parts of the tube 2|. It will be understood that these other paths are formed by the electrostatic capacity between the grid 23, the plate 24, the cathode 22, and the structure of the tube 2| itself.

A portion of the negative charge acquired by the grid 23 will remain during the next half-cycle 2 which time the plate 24 becomes positive and the grid 23 becomes negative. Finally an average negative potential of the grid 23 will result when a balance is finally reached between the number of electrons bombarding the grid 23 during the half-cycle when it is positive and the number of electrons which it loses due to leakage. It now the voltage which is applied between the cathode 22 andthegrid23isincreasedtherewillbean increased thermionic flow to the grid from the cathode 22 during the half-cycle when the plate 24 is negative, more electrons will remain on the grid 23 during the next half-cycle and as a result the averagenegative grid voltage is increased with a consequent result of a decrease intheflowofcurrent throughthe valve 2| during the half-cycle when the plate 24 is positive.

After a very few cycles of the alternating current the balanced condition will be reached and a constant current will flow through the tube 2| and through the load circuit including the relay 3|. Assuming now that light rays are directed onto the plate 24 as indicated in the drawings, there will be an emission from the plate 24 during the half-cycle when it is negative and the grid 23 is positive relative thereto. Additional electrons will, therefore, be received by the grid 23 in addition to those which it is receiving during this half-cycle from the cathode 22. As a result the grid 23 will become still more negative than before. In other words the average negative voltage of the grid 23 will be increased relative to the cathode 22. During the next half-cycle when the plate 24 is positive, there will be a reduction in the number of electrons emitted by the cathode 22 and arriving on the plate 24 because oi the control exerted by the grid 23. 'lhis control will be a function of the number of electrons reaching the grid 234mm the plate 24 which, in turn, is a function of the intensity of the light rays. When the grid 23 is made suillciently negative relative to the cathode 22 no electrons from the cathode 22 will reach the plate 24 during the half-cycle when the.

plate 24 is positive and, therefore, no current will flow through the tube 2|.

A similar result occurs when the circuit connections shown in Figure 4 of the drawings are used. During the half-cycle when the grid 23 is positive, the grid 43 of'the "pilot tube 4i isalsopositive andasaresult thegrid 43 will receive a negative charge which will be conducted through conductor 43 to the grid 23. The average negative potential of the grid 23 relative to the cathode 22 will then be increased with a corresponding decrease in the conductivity of the tube 2!.

when the connections for the pilot" tube 41 are reversed, as shown in Figure 5 of the drawings, there will be an increase in the number of electrons which reach the plate 24 during the half-cycle when it is'positlve since the average negative potential of the grid 23 will be decreased. This decrease in the average negative potential of the grid 23 is due to the increased leakage from the plate 44 to the grid 43 during the half-cycle when the plate 24 is positive.

The functioning of the circuit shown in Figure 6 or the drawings may be explained on this same basis. For low illumination of the photo electric cell SI electrons will arrive on the anode 53 which is connected to the grid 23 during, the half-cycle of the alternating current when the plate 24 is negative and the grid 23 and the anode 33 are positive. For this range of operaflow in the load circuit results.

In the circuit shown in Figure 7 of the drawings the leakage eflect of the photo electric cell 5| alone controls the potential of the grid 23. Since the cathode 54 is connected to the grid 23, any illumination received thereby will cause an increase in the photo electric current between the cathode i4 and the anode'53 thereby forming a conducting path through which the negative potential on the grid 23 will be drained oil! with a consequent continued increase in the conductivity of the tube 2| as a function of the degree of illumination applied to the cathode 54.

The so-called grid circuit" seems to exert its influence on the operation of the tube solely through an electrostatic or capacity effect. A complete circuit is not necessary, in that the conductor 230 can be completely disconnected from any actual ground, and the same characteristic operation will follow. The ground, however, enables the apparatus to be operated with a lesser degree of capacity at the variable condenser 35. With conductor 23a disconnected from ground 23h, the condenser 33 must be adjusted close to its maximum capacity, whereas with the conductor 23 connected to ground, the condenser may be adjusted for a lesser amount of capacity. Assuming the apparatus to have 53 (Figure 8) in the grid circuit results in a plate current flow of approximately 10 or 12 mllliampereaand at this time the tube is not sensitive to light. As previously stated, a reversal of the connections of the secondary winding 23d or of the battery II in the grid circuit,

with no shunt established across the condenser 35, results in an increased plate current flow from its stand-by value to approximately 10 or 12 milliamperes.

The length of the conductor 23a exerts an appreciable influence on the performance 01 the apparatus. Increasing the length of this conductor apparently increases the positive condition of the grid 23 because it results in increased plate current flow. With this longer length of conductor, the plate current flow can be brought down to its normal stand-by value by increasing the capacity of the variable condenser 35. When the length of this conductor 23a is increased, the sensitivity or response of the tube 2i to light is reduced. The shorter the length of this conductor from the grid 23 to the adjustable condenser 35, the more sensitive the tube is to light changes.

In the above described embodiment of Figures 1, 2, 3, and 8, the tube 2| is functioning both in the capacity of a light sensitive device and as an amplifier. This follows from the fact that within this single tube two actions are taking place, namely, the light responsiveness of the tube is controlling the charged condition of the grid, and

the charged condition of the grid is controlling the plate current flow.

In accordance with the teaching of our invention, we contemplate an improved construction of grid controlled electron tube in which a photosensitive material is incorporated in the plate or is coated thereon during the manufacture of the tube. Such material may be caesium, rubidium or any of the well known photosensitive materials. Such a tube would preferably embody a cathode and a grid arranged more or less similarly to the arrangement of these elements in tubes 2| and 4 I, so that the grid would be in position to influence the electrons emitted from the cathode and in position to influence the electrons emitted from the photosensitive material of the plate. Such a tube would preferably have a larger opening in the top insulating cap, or would have the cap eliminated entirely, in order to permit a greater volume of light to fall upon the effective surfaces of the plate. The operation of such a tube would be generally the same as the operation of the tubes above described, except that the greaterconcentration of photosensitive material on the plate would result in a greater density of electron emission from the plate in the presence of light.

We believe our invention to be of a fundamental nature and broadly new. Accordingly, while we have illustrated certain preferred embodiments thereof and certain preferred methods of carrying the invention into effect, nevertheless it, will be understood that these are merely exemplary and that numerous variations and modifications may be made therein without departing from the broad scope of the invention.

1. Light sensitive apparatus including a tube comprising a filament, grid and plate, a transformer comprising a primary and two secondary windings, said primary winding being adapted to be connected to an alternating current supply circuit, a plate circuit connecting directly with said. supply circuit, a filament circuit connecting one of. said secondary windings with said filament, a grid circuit including the other secondary winding having one end connected to said filament, and a variable condenser connected between the other end of said latter secondary winding and the grid, said latter secondary winding impressing on said variable condenser a potential which is out of phase with said latter potential,

said apparatus functioning to reduce the flow of current in said plate circuit when said plate is subjected to light.

2. Light sensitive apparatus including a tube comprising a cathode, grid and plate, the surface of said plate which is subjected to bombardment by the electrons from said cathode being coated with a light-sensitive material, means for heating said cathode, a transformer comprising primary and secondary windings, said primary winding being adapted to be connected to an alternating current supply circuit, a plate circuit connected to said supply circuit, and a grid circuit connected with said secondary winding, one end of said secondary winding being connected to said filament, and a variable condenser connected between the other end of said secondary winding and said grid, said secondary winding impressing on said variable condenser a potential which is out of phase with said latter potential, said apparatus functioning to reduce the flow of current in said plate circuit when the light sensitive coating on said plate is subjected to light.

3. Light sensitive apparatus including. a tube comprising a cathode, grid and plate, the surface of said plate which is subjected to bombardment by the electrons from said cathode being, coated with a light-sensitive materiahmeans for heating said cathode, a transformer comprising two secondary windings, a plate circuit connected toone of said secondary windings, and a grid circuit connected to the other of said secondary windings, one end of said secondary winding being connected to said cathode, and a variable condenser connected between the other end of said latter winding and the grid, said latter winding impressing on said variable condenser a potential which is out of phase with said latter potential, said apparatus functioning to reduce the flow of current in said plate circuit when the light sensitive coating on said plate is subjected to light.

4. Light sensitive apparatus including a tube comprising a cathode, grid and plate, the surface of said plate which is subjected to bombardment by the electrons from said cathode being coated with a light-sensitive material, means for heating said cathode, a grid circuit and a plate circuit, separate transformers for energizing said circuits, said grid circuit including the secondary winding of the transformer individual thereto having one end connected to said cathode, and a variable condenser connected between the otherheating said cathode, a plate circuit including a source of alternating current, a grid circuit including a source of potential, said grid circuit comprising a first condenser connected between one terminal of said source of potential and the grid, the other terminal of said source of potential being connected to said cathode, said source of potential impressing on said first condenser a potential which is out of phase with the potential impressed on said plate, said apparatus responding to the presence of light on said plate by a reduction of current flow in said plate circuit.

6. Light sensitive apparatus including a tube comprising a cathode, grid and plate having a light sensitive coating, means for heating said cathode, a plate circuit including a source of alternating current, a grid circuit including a source of potential, said grid circuit comprising a condenser interposed between said source of potential and the grid, and means for changing the conductivity of said tube, in response to the presence of light on said plate by a reduction of current flow in said plate circuit.

'7. L ght sensitive apparatus including a tube comprising a cathode, grid and plate having a light sensitive coating, means for heating said cathode, means for impressing an alternating current potential on said plate, a condenser having one terminal connected to said grid, means for impressing on the other terminal of said! cona source oi. alternating potential between said second member and said common control elanent in such manner as to cause said control element to receive electrons from said heated member and said second member during the half cycle of the alternating potential when said second memher is negative relative to said heated member and said control element;

9. In apparatus of the class described, the combination of an enclosure, a heated cathode member within said enclosure ior emitting electrons, an anode member within said enclosure towards which said electrons are adapted to be proiected, said anode member also emitting electrons in the presence of light, a common control element disposed between said members for influencing the flow oi the electrons emitted from both of said members, and circuit means for connecting a source oi. alternating potential between said anode member and said common control element in such manner as to cause said control element to receive electrons from said cathode and said anode during the half cycle of the alternating potential when said anode is negative relative to said cathode and said control element.

10. A translating system comprising, in combination; an electric valve having an anode, a cathode and a control electrode, said anode being disposed to emit electrons on application of light thereto; means (or applying an alternating potential between said anode and cathode, means for biasing said control electrode to a potential negative with respect to said cathode, and means connected to be responsive to the change in current now through said valve on application of light to said anode. 1

11. A translating system comprising, in combination; an electric valve having an anode, a cathode and a control electrode, said anode being disposed to emit electrons on application of light thereto; means for applying an alternating potential between said anode and cathode,.means for applying an alternating potential between said cathode and control electrode opposite in phase to the potential applied between said anode and cathode, and means connected to be responsive to the change in current flow through said valve on application of light to said anode.

12. A translating system comprising, in combination; an electric valve having an anode, a cathode and a control electrode, said anode being disposed'to emit electrons on application of light thereto; means for applying an alternating potential between said anode and cathode; means for biasing said control electrode to a potential negative with respect to said cathode, impedance means interconnected between saidblasing means and said control electrode for decreasing the leakage oi negative charges therefrom, and means connected to be responsive to the change in current flow through said valve on application of li ht to said anode.

13. A translating system comprising, in combination; an electric valve having an anode, a cathode and a control electrode, said anode being disposed to emit electrons on application of light thereto; means for applying'an alternating potential between said anode and cathode, means for applying an alternating potential between said cathode and control electrode opposite' inphase to the potential applied between said anode and cathode,impedancemeans interconnected between said last named means and said control electrode for decreasing the leakage of negative charges therefrom, and means connected to be responsive to the change in current flow through said valve on application 01. light to said anode.

14. A translating system comprising, in combi nation, an electric valve having an anode, a cathode and a control electrode; means for applying an alternating potential between said anode and cathode, means for biasing said control electrode to a potential negative with respect to said cathode, means for increasing the negative potential 01 said control electrode as a function of light-intensity, and means connected to be responsivetothechange in current flow through said valve in response to change in said light intensity.

15. A translating system comprising, in combination, an electric valve having an anode, a cathode and a control electrode;.means for applying an alternating potential between said anode and cathode, means for applying an alternating potential between said cathode and control electrode opposite in phase to the potential applied between said anode and cathode, means for increasing the negative potential of said control electrode as a function of light intensity, and means connected to be responsive to the change in current flow through said valve in response to change in said light intensity.

16. A translating system comprising, in combination, an electric valve having an anode, a cathode and a control electrode; means for applying an alternating potential between said anode and cathode, means for applying an alter nating potential between said cathode and control electrode opposite in phase to the potential applied between said anode and cathode, impedance means interconnected between said biasing means and said control electrode for decreasing the leakage of negative charges therefrom, means for increasing the negative potential of said control electrode as a function of light intensity, and means connected to be responsive to the change in current flow through said valve in response to change in said light intensity.

17. A translating system comprising, in combination, an electric valve having an anode, a cathode and a control electrode; means for applying an alternating potential between said anode and cathode, means for applying an alternating potential between said cathode and control electrode opposite in phase to the potential applied between said anode and cathode, impedance means interconnected between said last named means and said control electrode for decreasing the leakage or negative charges therefrom, means for increasing the negative potential of said control electrode as a function 01' light intensity, and means connected to be responsive to the change in current flow through said valve in response to change in said light intensity.

FREE) B. AUBERT. JEROME ROSSE'I'II.

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