US2204422A - Radio signaling system - Google Patents

Description

A. -v. LO UGHREN El AL RADIOSIGNALING SYSTEM Filed June so, 1953 June 11, 1940.

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, Patented June 11, 1940 UNI-TED STATES PATENT OFFICE .2, .204,422 1 RADIO SIGNALING SYSTEM 7 i Arthur V, Loughren, Moorestown, and Jerome C. Smith, Merchant'ville, N. J., assignors to Radio Corporation ofAmerica, a corporation of Delaware Application June-.30, 1933, serial no. 678,406-

16 Claims; .(01. 179-471) higher frequency signals. To correct this operat ing characteristic in signaling systems wherein .a

more uniform frequency characteristic is desired,

regeneration may be provided in connection with certain of the tuned circuits, as shown, fore-xample, by Landon U. S..Patent 1,702,445, wherein a tuned neutralized radio frequency amplifier is provided with controlled regeneration means for increasing the selectivity and the general operating efficiency of such a system. In the system disclosed in the Landonpatent, neutralization is provided in each amplifier stage, and regeneration is obtained by means of auxiliary electric discharge devices and associated circuits, for each stage. 1

The use of controlled regeneration, particularly for increasing the selectivity throughout certain operating ranges of a tuned radio frequency signaling system, or generally forproducing controlled oscillations in a tuned circuit, .is desirable, as was recognized by Landon, and, has been indicated by subsequent developments in-the art. vItis, therefore, an object of the present inventionlto provide an improved controlled regenerative amplifier system which obviates certain dis advantages of systems of that character heretofore known, such as circuit complications and an additional electric discharge device or tube requirement, or critical or unstable operating characteristics. 7 r

The patent to Landon, above referred .to, also discloses the application, of regeneration to a plurality of amplifier stages in what maybe termed a multiple regeneration system, and it is afurther object of the present invention to provide an improved and simplifiedregeneration system of that charactenWhich is readily adapted, for application to a plurality of amplifier stages.

In a tuned radio frequency amplifier, which represents any amplifiersto which the advantages of regeneration may be applied and the present preferred system to which theinvention is readily applicable, the selectivity throughout a certain frequency range, such as the broadcast receiving band referred to, may Vary greatly. In the broadcast band, as pointed out, the selectivity at the low frequency end of the range, for example at 600 kc. is much greater than at the high frequency end of the range, forhexample at 1400.;kc.

, It-is, "therefore, a further jObjBCt'Of the present invention to provide a tuned high frequency, amplifier of the character above'referr'ed to that shallzprovide, economically and by simple means, substantially the same desirable si'electivitylatv the high frequency end'of the tuning rangeas it does at the low frequency end of the tuning range. 1

Itis also desirable, in certain amplifying systems, to control the signal .output of an amplifier stage and, accordinglylit is a still furtherobject of the present invention to provide. an amplifier stage-wherein controlled regeneration 'may be applied toincrease the, operating efficiency thereof, and independently of the controlled regenerathe stage may be controlled,

ii x.

20 tion, the signal transmission efficiency or gain of The gain control feature above noted is desirable not only in signal amplifiers and the like, but in other electric discharge amplifier'circuits wherein controlled regeneration maybe utilized,

such as in an oscillator or oscillation generator circuits, for example. It'is, therefore, a further object of the present invention to providecontrolledregeneration and amplification control in an improved oscillator or signal generator-"'- system,

In one embodiment of the invention, in connection with a radio frequency amplifier, each stage thereof is isolated by suitable and substantially complete shielding, and then an appropriate amount of regeneration is introduced into each tuned circuit to produce the desired regeneration effect. If the regenerationvaries with the signal frequency in the proper manner, selectivity may be made equally good atall points'in the range to be covered by the amplifier system. Resulting variations in the sensitivity of such a system, if any, may be compensated for by proper design ,of the interstage coupling'means.

In accordance with the invention, in each regenerated shielded amplifier stage, an electron discharge device of the high gain type, having suitable electrode elements, is employed in conjunction with a feed-back circuit, whereby the device may function to provide an effective amplifier and electrically coupled regeneration means.

Instead ofthe additional regeneration tube heretofore considered necessary, or complicated regeneration circuits, a'simple feed-back circuit anode, three other electrodes one of which is a screen grid, another of which is a control grid,

and with a fifth element adapted to provide an anode and having a certain mutual conductance with respect to the control grid. The feed-back or regeneration circuit is provided in connection with this electrode and may then be so designed that its regeneration control upon the system may be in a direction to emphasize a desired end of the signal frequency range whereby substantially constant selectivity may be maintained.

The invention will, however, be better understood from the following description when considered in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing,

Fig. l is a schematic wiring diagram illustrating a tuned high frequency amplifier stage embodying the invention;

Fig. 2 is a similar wiring diagram showing the application of the invention to a multi-stage tuned high frequency amplifier in a modification of the circuit of Fig. 1; and

Fig. 3 is a schematic wiring diagram of a further modification of the circuit of Fig. l to provide a controlled oscillator.

Referring to Fig. 1, 5 indicates a shielded, tuned, radio or high frequency amplifier stage connected with a source of signals such as output terminals 6 of a preceding amplifier or signal source indicated at 1, and having output terminals 8 connected with a load or utilization device, such as a succeeding amplifier stage indicated at 9.

In accordance with the invention, a single electric discharge device or electronic tube 'IB is employed in the amplifier stage 5 and is so arranged in circuit between the terminals 6 and 8 that it may provide not only substantially uniform frequency band amplification in the signal channel in which the stage 5 is connected, but controlled regeneration for increasing the efilciency of the stage.

In the present example, the device I is of the five electrode type having, in addition to the usual cathode or electron emitting element II, a control grid I2, a screen electrode I3, an anode I4, and a space charge grid I located between the cathode II and the control grid I2, This may be a type of radio tube known as a pentode, as hereinbefore described.

Pentode tubes are well known and are described on page 5 of the publication The RCA Radiotron--Cunningham Radio Tube Manual, Technical Series No. RC-ll.

As referred to in the above manual, the pentod tube is provided with three electrodes between the cathode and the anode, these electrodes being nominally a control grid, a screen grid, and a suppressor grid in that order preceding from the cathode to the anode. The suppressor grid is therefore the grid adjacent to the anode and, as is well known, is connected with the cathode for the suppression of secondary emission.

In the present system the electrode I3 is that grid which is normally utilized as a suppressor grid and in the drawing occupies the position of the usual suppressor grid. However, in the present example the electrode I3 is utilized as a screen for the anode. A pentode type of tube is therefore particularly well adapted for use in a system embodying the invention.

As is known in the art, the space charge grid I5 may Ioe employed for the purpose of increasing the mutual conductance of the device. In accordance with the invention, however, an im portant additional use is made of this grid, namely as a source of energy for regeneration purposes. If, as is contemplated, the device I0 is so designed that the anode I4 is well shielded by the screen grid I3 from the remaining elements of the de vice, then no reaction from succeeding amplifier stages, such as the stage 9, can be fed back into the stage 5 to interfere with any condition of regeneration Which may be established in the stage 5.

In carrying the above described system into efiect in an amplifier stage such as that of the present example, the control grid I2 and a suitable electrode to be employed for regeneration purposes, such as the space charge grid I5, are electrically coupled whereby energy may be supplied from the oneto the other. In the present example, the control grid I2 is connected with a tuned input circuit I6 comprising a variable tuning capacitor I'I connected in shunt relation to a winding I8 of an input coupling transformer I9 which is connected with the terminals B as the signal source.

The grid or input winding I8 is inductively coupled, as indicated by the arrow, with a regeneration or feed-back winding 20, connected with the space charge grid I5 in a regenerative plate or feed-back circuit 2|.

Through the output terminals 8, the anode I4 is connected with an output or load circuit 22, in which is included a coupling device 23 for the utilization device or stage 9. Operating current at suitable potentials for the device I0 is provided from a source indicated by a pair of supply terminals 24. A potential divider means 25 is connected in shunt with said terminals and suitable connection with the various electrodes of the device for applying thereto proper operating potentials is made at various points thereon, as indicated.

In the present example, the cathode II is connected with a tap 26 which is more positive than a tap 21 for the control grid I2 and its input or grid circuit I6 which, as indicated at 28, is operated at ground potential. The tap points 29 and 30, for the space charge grid or regeneration anode I5 and the main anode I4, respectively, provide potentials which are more positive than the cathode. The screen grid I3 is operated also at a positive potential which is preferably variable, being connected to the variable tap point 3| through a supply lead 32. Suitable bypass capacitors indicated at 33 are provided between the various circuits and cathode to prevent undesired coupling through the supply source.

In the present embodiment of the invention, the inner or first grid I5, normally known as a space charge grid, is utilized as a regeneration plate electrode and is connected with a potential source more positive than the cathode, as above described. The feed-back coupling means, which in the present example is the winding 20, serves to supply energy to the input circuit I6 through its coupling with the coil I8.

It has been found that this feed-back arrangement is substantially independent of the operation of the device as a signal amplifier and that the amplified signal output through the circuit 22 from the main output anode 14 may bevaried also, independently, by variation of the potential on the screen grid l3 by adjustment of the variable contact 3|.

The combination of regeneration in the input circuit and independent control of the amplifier gain or output signal level witha single electric discharge device for each stage, permits an improved control of the gain and an improved operating efiiciency to be obtained in a radio receiving system or other signaling apparatus embodying high frequency amplifiers of the electric discharge type. Y

- In this embodiment of the invention also, the second or middle grid is utilized as the control grid, while the outer grid functions as a screen and gaincontrolling electrode or grid. It will be noted that the first or spacecharge grid, as a regeneration plate electrode, as above mentioned, is electrostatically shielded from the main output anode I4, by'the screen'grid structure. However, whilethe transductance of" the device I is, therefore, variable through variation of the controlling potential on the screen or outer grid l3, as above described, at the same time, the

transductance of the device through the space charge grid or regeneration anode I is substantially independent of the control of the transis utilized in a receiving system high frequency signal channel in multiple, the advantages of a control system above mentioned may be more readily appreciated. 1

In the receiving system shown, a high frequency, tuned, .multi-stage amplifier is provided,

embodying two cascade connectedshielded stages each provided with a single electric discharge amplifier 31 and 38 of the multiple grid type providing controlled regenerative amplification and gain like thatof the amplifier shown in Fig. 1. The circuits employed are substantially like that shown in Fig. l and differ therefrom only to the extent that the circuits are adapted for multiple control of gain and of bias, together withcontrolled regeneration anode current, and further, with an electrode arrangement abovementioned, in which the first or inner grid is utilized as a control grid.

Each of the electric dischargedevices 31 and 38,'is of the multiple grid type, having a heated cathode 39, a first or inner grid 40, a second grid 4|, and a third or outer grid '42 adjacent to an output anode 43. Since the stages 35 are identical in circuit arrangement and construction, the same reference numerals are otherwise applied to each stage and to the circuit and electrode elements therein.

The tubes shown may be the usual pentode type of tube wherein the grids '42 are normally utilized as suppressor grids while the as screen grids.

Each of thedevices 31 and 3B in the stages 35, is provided with a tuned input circuit indicated at 44 in connection with theinner or first grid 40. A suitable feed-back coupling means 45 or coupling coil is associated with the tuning grids 4! are utilized 4 inductance 46 for the-input orgrid circuit 44 and is provided with operating anode current through a resistor 41 in connection with a high potential supply lead 48, V

The low'potential side of the supply circuit is indicated at 49 and is the ground or low potential lead forthe receivingchannel and system. The

cathode 39 is returned to this lead through a self bias;resistor-50, while the input circuit 44 is returned directly thereto through the lead 5l -I whereby self-biasgridpotentials are provided for thecontrol grid 40 from the resistor 50. r The output anode43-for the device 38 is connectedwithja succeeding stage or utilization device through an output circuit 52 in which is shown an'interstage coupling means comprising two windings 53and 54, providing inductive and capacitive coupling, respectively, with the input circuit 44 of the succeeding stage as shown. Anyother suitable coupling means maybe employed which provides for substantially uniform signal transfer over. the frequency operatingrange of the amplifier.- t t The second of the two stages shown is provided with anoutput circuit 55 which may be connected with any suitablecoupling means like that for the preceding; stage. Suitable bypass capacitors indicated at 5 6' are provided in connection with the cathode, for the regeneration and input circuits and also-for .theouter or screen grid 42 of each of. the devices 3! and 38. The latter "grids receive operating and control potentials through supply leads 5'! from the variablecontacts 58' of separate potentiometer means 59, each connected across thepotential supply leads 48 and 49 in parallel. I

The variable contacts 58 of the potentiometer devices 59 are 'a1so.connected for simultaneous gang operation as indicated by the'dotted connection 60 and the operating knob 6|, whereby the gain or signal amplitude for each ofthe stages .35 may simultaneously be controlled.

In this embodiment of the invention the series resistor 41 in the regeneration anode circuit serves to prevent the regeneration current from rising when the screen grid potentials are reduced below a. predetermined value by operation of the potentiometer contacts 58. This is for the. reason that as the screen grid potential is reduced, the electrons from the cathode 39 tend to travel to the second grid orregeneration anode 4| instead of v second grid, therefore, is operated preferably at a positive potential somewhat less than the main anode potential; This potential may be in the order of or greater than that applied to the screen grid 42. The. impedance or resistor. 4! should provide a potential drop which is relatively high compared with the internal drop in the tube or electric discharge device itself, so that the impedance ,or resistor 41 serves effectively to control the regeneration current as the screen grid potential is varied.

The screen or outer grid potential is variable through the operation of the potentiometer means ing structure between the main output anode 43 and the auxiliary or regeneration anode means provided with the grid 4|,

, The mutual conductance or trans-conductance of f the second grid 4| is less than that of the first grid 40 so that in the circuit of the present example, as distinguished from that shown in Fig. 1,' the coupling for regeneration purposes with the input or grid circuit may be increased without overloading the regeneration circuit. This may be accomplished because of the higher impedance of the second grid 4| in the present type electric discharge devices available, which impedance may be of the order of 40,000 ohms as compared with the impedance of the first grid of approximately 1000 ohms with respect to the cathode.

' Furthermore, with this circuit arrangement, the normal current flow to the first grid 40 may be of the order of two to three milliamperes as com-pared to twenty to thirty milliamperes for the circuit of Fig. 1, wherein the first grid is utilized as the regeneration anode.

In either embodiment of the invention, however, it will be seen that the electric discharge amplifier device employs a plurality of grid electrodes in addition to the usual anode and cathode, and that one of the grid electrodes serves as a screen grid structure between the main output anode and the auxiliary regeneration anode provided by another of the grid electrodes, while a third grid electrode is employed as a control grid for the amplifier device.

A regeneration coupling means is provided between the auxiliary anode electrode and the input circuit or control grid and independently of the regeneration adjustment the signal output or gain of the stage is then adjustable by varying the potential applied to the "screen electrode structure.

In a cascade amplifier for the high frequency receiving circuit of a radio receiver, a relatively high gain per stage is effected and the regeneration effect and the resulting selectivity may remain substantially constant while the overall gainmay be controlled simultaneously in each stage as shown. An impedance element in the regeneration anode circuit efie'ctively maintains a substantially constant mutual conductance at substantially all control positions of the gain control means. a V

In the system of the present example the first amplifier stage 35 is supplied with signal energy through any suitable means such as a first stage amplifier device 02 whichis coupled through a suitable tuned input circuit 63 and coupling means i l of a signal collecting means indicated by an antenna 65 and a ground connection there for (it, the latter being a continuation of and connected with the low potential lead 09.

The amplifier device 62 may be of any suitable type and is in the present example provided with a cathode 61 having a self-bias resistor 63 in circuit therewith, a control grid 59 connected. with the input circuit 63, a screen grid '10 which receives operating potential from a tap H on the potentiometer 59 for the first amplifier stage 35 through a supply lead 12 and which is further provided with an output anode 13 also connected through an output M with the high potential supply lead 48.

In the output circuit is provided a suitable coupling means with the first output stage 35,

and in the present example this coupling means is provided by an electromagnetic coupling winding 53 associated with the input circuit inductance 56 and an electrostatic coupling winding 54 also associated therewith. As hereinbefore pointed out, this coupling means is arranged in any suitable manner to provide substantially uniform transfer of energy throughout the signal range over which the amplifier is designed to operate. I

It will be appreciated that in case further controlled regeneration and gain may be required in the system, further stages may be provided like those shown at 35, and the input amplifier 62 may, under certain operating conditions, be arranged in the same manner as the succeeding stages. The manner of coupling in operation is obvious from the description of the two stages as shown and involves merely a duplication of either of the stages shown at 35 together with an additional control or multiple connection for the control grid of the additional stage.

Likewise, other suitable electric discharge de vices of the multiple electrode type may be employed in each amplifier stage, and the invention is, therefore, not limited to the use of a pentode type of amplifier. Any amplifier having the electrodes as described hereinbefore may be employed.

Therefore a system embodying the invention may have the advantage or high selectivity and gain with controllable signal output adapted for multiple stage operation without efiecting the regeneration or selectivity and without involving the use' of additional electric discharge devices for that purpose.

Referring now to Fig. 3, the controlled regeneration may be applied to an oscillator having a pentode device having a cathode 16 of the heated type in the present example, a control grid H, a main output anode electrode T8, a

shielding electrode or screen 19 surrounding the anode electrode 18, and isolating it from the remainder of the electrodes in the device, and an additional grid electrode 80 which in the present example is a second grid.

As shown in Fig. 3, this embodiment of the invention employs the second grid 80 as an auxiliary or regeneration anode, and is connected through a coupling condenser ill to oneend 82 of an oscillatory circuit 83, while the opposite terminal 84 thereof is connected'to the control grid Tl through the usual grid leak and condenser combination indicated at 85. The anode circuit for the grid electrodeBil is connected with any suitablesource of potential through a lead 80, in which is located a high frequency choke coil 81 providing the coupling impedance for the coupling condenser 8 I The oscillator circuit is provided with the usual tapped grid-plate inductance 88 which is connected to a cathode return lead 89 through a lead 90.

The main output anode circuit for theanode i8 is indicated at 9| and output signals are available between the lead SI and the ground lead 89 in the circuit of the present example as output leads. It will be noted that the screen grid structure 19 effectively surrounds the output anode 78 and is connected to the cathode lead 89 through a supply lead 92 and a variable source of biasing potentials provided by any suitable means, such as a battery 93 and a variable potentiometer device 94 connected in shunt thereto'with the variable contact 95 thereof connected with the supply lead 92. The battery is provided with. a center tap 96 which-is connected I 2,204,422 I to the cathode return leacl-89 through a grounded desired inthe low frequency end of the range, the

return lead 91' whereby as the potentiometer contact 95 is moved between the extreme limits or terminal ends of the potentiometer device, suitable negative and positive potential may-be applied .to the screen gridstructure to control the oscillation output of the oscillator between wide limits.-.

It will'further be'noted that the oscillator is provided with a shield enclosure indicated at 98, which is also connected to the cathode return lead 83 and is arranged to cooperate, as indicated,

with the screen grid structure lg to electrically isolate the output anode and the output circuit 9| therefor'from the remaining electrodes of the electric discharge device'and the oscillator circuitfl'3. This may be arranged in any suitable manner such as by having-the shield 93 terminate adjacent to the device I5 andin direct association with the screen structure l9 as indicated diagrammatically in the drawing. With the oscillator circuit or'oscillator genera-- tor' system arranged as shown, the oscillation frequency established in the generator circuit 83 is-substantially independent of the oscillation signal outputcircuit 9i and'the amplitude of the oscillations delivered to the circuit 9| may be controlled between wide limits without affecting the frequency adjustment of the circuit 83 for which a usual shunt condenser 99 in conjunction with the coil 83is provided.

' As the operation of the oscillation generators is known and understood, further description of the operation is believedfto be unnecessary. However, it should be-pointed; out that'in; providtions are produced, and the signal output anode.

In this connection, therefore, it is preferable to employ a multiple g'rid'electrode electric discharge device. and to employ the first or inner grid as the control grid, whilethe next adjacent or second grid is utilized as the feed-back or oscillation anode, and between these two electrodes any suitable oscillation generator circuit may'be provided; By controlling the potential applied to the screen grid structure associated with the output anode electrode, the signal amplitude for energy may effectively be controlled combination, an electronic tube amplifier device between wide limits without afiecting the frequency setting cuit. I

- It should further be noted that in providing the 'feed-back coupling, a fixed coupling means is employed. Any other coupling means may, however, be employed, as hereinbefore explained.

* A fixed coupling has the advantagein certain amplifiers, such as a tuned high frequency amplifier shown in Fig. 1, that a sufiicient amount or regeneration is obtained at or inthe higher frequency end of the tuning or operating range of the system through'a proper degree of cou-- pling toprovide a desired selectivity efiect in this range Where the selectivity is ordinarily lower than at or in the low frequency end of the tuning or operating range of the system.

The regeneration efifect' is permitted by the,

fixed coupling to decrease with a decrease in frequency so that'at' orfin-the low frequency'end of the tuning rangesubstantially no regeneration is obtained. Since the selectivity is ordinarily as of; the oscillation generator cirselectivity of the system is thereby rendered substantially flat or uniform throughout: the tuning or operating range. I f

Otherembodiments-of the invention will readily be apparent to those skilled in the art and, therefore, the invention is not limitedto theparticunal input :circuit connected between the cathode andone of said grid electrodes, means providing a regenerative feed-back coupling between another of said grid electrodes and said input circuit,'means for applying a positive potential with respect to cathode on said last-named electrode, means for applying a variable controlling potential to a. third grid'electrode more adjacent to the main outputanode, and a signal output circuit connected with said output anode.

2. In a' radio signaling system, an electric dis--- charge amplifying stage comprising an electric discharge amplifier device having a cathode, an anode, a control grid, a second grid adjacent "thereto and a-screen-grid adjacent to the anode,

a signal input circuit connected with the control grid, a signal output circuit connected with the anode, means providing a regenerative electrical coupling between the second'grid and said input circuit, andjmeans for applying operating potentials tosaid electrodes including a positive potential on said second-grid electrode less, than the anode potential and a variable potential on said'screen grid. v

3.. In a radio signaling system, anelectricdis- I charge amplifying stage comprising an electric discharge amplifier device having av cathode, an anode, a control-grid,'a space charge gridand a screen grid adjacent to the anode, a signal input circuit connected with the control grid, a signal output circuit connected with the anode, means .providing a regenerative electrical coupling between the space charge grid and said input-circuit, means for applying a positive operating po tential' with respect to cathode to said space positive potential tosaid screen grid. y

4. An, electric signal amplifier comprising in having a signal input electrode'and a-sig'nal out put electrode, ascreen electrode for said output electrode and an electrode providing a regeneration anode, means providing a regenerative electrical; coupling between said regeneration anode charge grid, and means forapplying a-variable mutual conductance with respect to the control f grid electrically coupled 'to said grid circuit to supply feed-back electrical energy thereto-for regeneration below the point, of oscillation, means in circuit with saidadditional electrode fer limiting currentflow thereto, and means for applying to the grid more adjacent to the anode a variable potential for controlling the mutual conductance of said device and the signal flow through said amplifier. ,6. A radio signaling system including. in combination, a plurality of cascade connected electric discharge amplifier stages, each of said stages being electrically shielded and including an electric discharge amplifier device having a signal input circuit and a signal output circuit, means for coupling an electrode of said device other than an output electrode with said input circuit to provide regeneration, means for applying a varying gain controlling potential to another electrode of said device, and means for simultaneously operating each of said last named means in each stage.

7. A radio signaling system includingin combination, a plurality of cascade connected ampli fier stages, at least one of which is shielded from another and each of which comprises an electric discharge amplifierdevice having a cathode and a signal input electrode, a signal output electrode, a screen electrode adjacent thereto, and an additional electrode, means providing a regenerative electrical coupling between said additional electrode and the input electrode at signal frequencies, current limiting means in circuit with said additional electrode, means forsupplying operating potentials to said screen electrodes, and means for simultaneously varying said last named potentials in each stage.

8. A radio signaling system including in combination, a plurality of cascade connected amplifier stages, at least one of whichis shielded from another and each of which comprises an electric discharge amplifier device having a cathode, a signal input electrode, a signal output electrode, a screen electrode therefor and an additional electrode, means providing a regenerative electrical coupling between said additional electrode and the input electrode at signal frequencies, current limiting means in circuit with said additional electrode, means for supplying operating potentials to said screen electrodes, and means for simultaneously varying said potentials in each stage, said last named means comprising a potentiometer device connected with said supply means and having a variable tap point connected with one of said screen electrodes.

9. The combination with an electron discharge device having a control grid, a main anode and an auxiliary anode, of a signal input grid circuit connected to said grid, means for rendering the transductance between the auxiliary anode and the control grid substantially constant in response to variations in the transductance between the control grid and the main anode, said means including a unitary screen grid structure interposed between said anodes and between the main anode and the control grid, means for applying a variable positive potential to the screen grid structure, and means for applying substantially a constant current to the auxiliary anode. 10. In a tuned high frequency amplifier, the combination of an electronic tube amplifier device having a signal input electrode and a signal output electrode, a screen electrode for said output electrode and an auxiliary electrode, means providing a predetermined regeneration coupling between said auxiliary electrode and said first named electrode whereby substantially uniform selectivity is provided by said amplifier throughout the tuning range thereof, and means connected to the screen electrode for applying a variable potential thereto, whereby the signal output from said output electrode may be varied independently of said electrical coupling.

11. In a radio signaling system, an electric discharge amplifying stage comprising an electric discharge amplifier device having a cathode, an anode, a control grid, a screen grid and a suppressor grid, a signal input circuit connected with the control grid, a signal output circuit connected with the anode, means providing a regenerative electrical coupling between the screen grid and said input circuit, means for applying a positive operating potential with respect to cathode to said screen grid, and means for applying a variable controlling potential to the suppressor grid.

12. In an electric discharge amplifier, the combination of an-electric discharge device having a cathode, an anode, a control grid, a grid structure adjacent to the anode and an auxiliary anode electrode interposed between said grid structure and the cathode, means providing regenerative feed-back coupling below the point of oscillation between the control grid and the auxiliary anode electrode, a signal input grid circuit connected with said control grid, an output circuit connected with said first named anode, and means for applying a variable potential to the said grid structure whereby the electrical output through said output circuit may independently be varied.

13. A radio signaling system including in combination, a plurality of cascade connected electric discharge amplifier stages, each of said stages being electrically shielded and including an electric discharge amplifier device having a signal input circuit and a signal output circuit, means for coupling an electrode of said device other than an output electrode with said input circuit to provide regeneration, and means for applying a variable gain controlling potential to another electrode of said device.

14. An electric tube amplifier system including in combination, a signal input grid circuit, a regenerative feed-back circuit coupled to said input circuit, a suppressor grid circuit, and means for supplying a variable controlling potential to said suppressor grid circuit.

15. In an amplifier system, an electron discharge amplifier circuit comprising in combination, a tunable signal input grid circuit, a screen grid potential supply circuit regeneratively coupled to said grid circuit, a suppressor grid potential supply circuit, means in said last named circuit for Varying the potential of said circuit,

and a signal output anode circuit.

16. In an amplifier system, the combination with an electron discharge device having a cathode, an anode, a control grid, a screen. grid, and a suppressor grid between said cathode and anode, of a signal input grid circuit connected with said control grid, means including said input grid circuit for regeneratively coupling said control grid and screen grid, a signal output circuit connected with the anode, and means for variably controlling a potential on said suppressor grid to variably control the amplitude of signals applied to said output circuit.

ARTHUR V. LOUGHREN. JEROME C. SMITH.

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