US2017523A - Amplifier - Google Patents

Description

0%. 1'5, 1935. G, BEERS 2,017,523

AMPLIFIER Filed Jan. 26, 1952 2nd Dete cTor AUDIO 2 nd DetecTor AUDID AAAAAA INVENTOR.

George L.Bee1"3,

J I I ,r s ATTORNEY.

Patented Oct. 15, 1935 UNlTED STATES PATN OFFICE AMPLIFIER of Delaware Application January 26, 1932, Serial No. 588,909

41 Claims.

My invention relates to amplifiers and, more particularly, to amplifiers of the type suitable for use in the reception of radio signals.

In the design of radio receivers, there are two highly desirable characteristics that, in a sense, are mutually exclusive-that is, a receiver must be sufiiciently selective to differentiate between incoming signals under maximum and minimum sensitivity conditions and, at the same time,

1 high fidelity and freedom from distortion are desirable.

Heretofore, fair fidelity has been attained through the use of inter-tube coupling circuits having bandpass characteristics. It has been diflicult, however, to so design receivers, especially those provided with automatic volume control, which will exhibit a high degree of fidelity, as well as reasonable selectivity, when receiving signals from local stations and still be sufficiently selective to receive weak signals from distant stations without an unpleasant amount of background noise.

It is, accordingly, an object of my'invention to provide a radio receiver wherein high fidelity is automatically had during the reception of strong signals, without detriment-ally influencing the selectivity.

Another object of my invention is to provide, in a radio receiver, means for automatically increasing the selectivity during the reception of weak signals.

Another object of my invention is to provide a volume control system that shall function satisiactorily without affectingv the characteristics of the amplifying tubes.

Another, and more specific, object of my invention is to provide a radio receiver that, in addition to the features enumerated above, shall have automatic volume or gain control.

The foregoing objects, and other objects ancillary thereto, I prefer to accomplish, in part, by supplying to the grids of certain of the electronic tubes in a radio receiver grid-biasing po- 45 tentials controlled as to their amplitude by incoming signals. 1 also utilize the incoming signals to automatically control the damping in certain of the inter-tube coupling circuits and, concurrently therewith, the transfer of energy to between the tubes.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and 55 its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment, when read in connection with the accompanying drawing, wherein Fig. l

is a diagrammatic view of a portion of a radio 5 receiver embodying a preferred form of my invention, and Fig. 2 is a diagrammatic View of a receiver circuit embodying a modified form of my invention.

Although my invention is susceptible of appli- 1o.

quency amplifier tubes I, 3, 5, and I, and a detector tube 9. Each of these tubes may be of the screen grid, equi-potential, cathode type having an anode II, a screen grid I3, a control grid I5, an electronically active cathode I1, and a heater I9. Preferably, however, the detector is of the three element type, as illustrated.

The several heaters, as is well known to those skilled in the art, may be supplied with alternating current from any convenient low-potential source (not shown).

The first two tubes of the series are preferably connected through the medium of a radio frequency transformer 2!, the primary and secondary windings of which are tuned and the coupling between them so adjusted that the transformer efficiently passses a band of frequencies l0 KC above and below the chosen intermediate frequency. The second and third intermediate frequency tubes are impedance coupled, the coupling network including a tuned circuit 23 connected directly to the anode of the second tube and, through a coupling condenser 25, to the control grid of the next tube.

The third and fourth intermediate frequency amplifier tubes are connected through a transformer 21 substantially the same as that between the first and second tubes, and the last intermediate frequency tube and the detector tube are coupled through an equivalent transformer 29.

A source of anode and grid biasing potentials (not shown) is supplied, across the output circuit of which is connected a resistor 3|. Plate potential for the second, third, and fourth intermediate frequency coupling tubes is supplied over a connection 33 extending from the resistor, and the cathodes of these three tubes-also have a common connection 35 to a point on the resistor sufficiently more negativethan the point to which the anodes are connected to provide the necessary plate potential.

The detector is individually supplied with plate potential from the resistor, the primary winding of an output audio frequency transformer 31 being included in the supply circuit. The detector is provided with self-biasing means which, preferably, takes the form of a resistor 39 included between the cathode thereof and a point on the resistor.

The screen grids of the several intermediatefrequency amplifier tubes are, of course, provided with suitable positive potentials from the resistor, but the actual connections have been omitted from the drawing in order to simplify it.

If it is assumed, for the moment, that the first intermediate frequency amplifier tube l is supplied with plate potential directly from the resistor, and with grid biasing potential also directly from the same source, the system thus far described is of the type ordinarily found in the majority of superheterodyne receivers. Obviously, such a system responds to every change in the amplitude of an incoming signal and is devoid of means for automatically altering either the selectivity or the fidelity thereof in response to signal amplitude changes.

In order that automatic volume control may be had, it is necessary toprovide some means whereby the increase in signal amplitude or, more properly, in the amplitude of the carrier frequency, may be met and compensated by a change in gain. To this end, as disclosed in my application Serial No. 212,791, filed August 13, 1927, I provide a volume control tube 4| of the equi-potential type having an anode 43, a control grid 45, an electronically active cathode 41, and a heater 49. The grid of the volume control tube is variably connected through a resistor 5| to a point on the main potential supply resistor 3| more negative than the point to which the cathode is connected and incoming signals are applied thereto through a condenser 53 from the input circuit of the detector 9. I

The signal may, of course, be taken from any other point in the system illustrated or from a point on a preceding stage (not shown).

The anode of the volume control tube is connected over a resistor 55 to a point on the main potential supply resistor 3| more positive than the point to which the cathode is connected and the said anode is also connected to a conductor 5! common to the grid circuits of all the intermediate frequency amplifying tubes.

Preferably, the bias applied to the grid of the volume control tube is so chosen that the current flowing in the output resistor thereof during nosignal intervals is only enough to maintain the grids of the intermediate frequency amplifier tubes sumciently negative to provide maximum sensitivity. However, as soon as an incoming signal makes its appearance upon the grid of the volume control tube, the output current therefrom increases, with the result that the grids of the intermediate frequency amplifier tubes acquire a more negative potential measured by the potential drop acrossthe output resistor. The incoming signal, therefore, as it increases in amplitude, is met by reduced gain in the system, thus compensating for changes occasioned by fading and the like.

Since, as hereinbefore pointed out, a high de gree of fidelity is desirable when receiving strong signals from local stations, some means must be supplied whereby the damping in' theinter-tube networks is increased, or whereby the effective coupling between the primary and secondary winding of an inter-tube transformer is automatically tightened. To this end, I provide a plurality of thermionic devices 59 and 6!, the only function of which is to alter the condition of the coupling devices during the reception of strong signals from local stations. These devices are hereinafter referred to as the first and second fidelity-control tubes.

The fidelity control tubes may be of the equipotential cathode type having an anode 63, a control grid 65, a cathode 61, and a heater E59 and the first tube is so disposed with respect to the output circuit of the second intermediate frequency amplifier tube 3 that the space current path therein is connected eifectively in shunt to the tuned output circuit 23 of the said tube. Plate potential for the first fidelity control tube, accordingly, is supplied over the common conductor 33 which supplies plate potential to the second, third, and fourth amplifying tubes.

The input circuit of the first fidelity control tube includes a resistor H which is serially connected between the output circuit of the first intermediate frequency amplifying tube I and a point on the anode supply resistor. The cathode of the tube may be connected to a point on the resistor slightly more positive than the point to which the input resistor connects, in order that the tube may be biased normally to a desired point.

Since the space current path in the first fidelity control tube is connected in shunt to the output circuit of the second intermediate frequency amplifying tube, the impedance of this path controls the damping in the said circuit, and also controls the energy transfer between the second and third tubes. In order that the impedance may be a function of the amplitude of an incoming signal, the previously mentioned connection, including the resistor H, between the input circuit and the first intermediate frequency amplifier tube is made.

The connection of the cathode 61 to the resistor 3| may be provided with manual adjustment to control the bias on the grid 65, if desirable. If this is done, tone and selectivity control may be had at the will of the operator.

The first fidelity control tube functions as follows:

Normally, as before explained, the grids of the intermediate frequency amplifying tubes are supplied with just the right amount of negative potential to maintain the said tubes in best condition for the amplification of weak signals. Such being the case, a definite amount of space current flows in each of the said tubes, the space current in the first tube, obviously, flowing through the input resistor l I of the first fidelity control tube. By proper choice of the magnitude of the resistor H, the drop in potential thereacross, when added to the bias potential derived from the supply resistor 3!, the grid of the first fidelity control tube may be so biased that the plate impedance of the tube is relatively high during no-signal intervals or during the reception of weak signals.

The selectivity of the system, therefore, insofar as the first and second tubes are concerned, normally is high, which is a desirable condition for weak signal reception, to eliminate background noise, as already pointed out.

7 However, as soon as the system is tuned to a strong signal, the plate current in the volume control tube 4| increases, as previously explained.

with the result that the bias applied to the intermediate frequency amplifying tubes becomes more negative, thus reducing the average plate current from the first intermediate frequency amplifying tube which occasions a decrease in the potential across the resistor II in the input circuit of the first fidelity control tube.

The plate impedance of the last-named tube, therefore, decreases, permitting the tube to exert an increased shunting effect, at the intermediate frequency, upon the output circuit of the second IFA tube. The tuning of the output circuit, therefore, is broadened and the fidelity of reproduction increased while, at the same time, a decreased amount of energy is transferred to the third IFA tube.

Since the decrease in energy transfer between he second and third tubes further reduces the gain in the system below the reduction occasioned by the more negative grid bias supplied to the tubes from the volume control tube, it may be desirable to provide further means whereby the decrease in gain may, to some extent, be compensated without impairing the fidelity of response of the system.

I, accordingly, provide the second fidelity control tube 6|, the space current path of which is effectively connected in shunt to the primary winding of the transformer 2'! interposed between the third and fourth IFA tubes.

The transformer, as illustrated, comprises a tuned primary winding which may have a resistor 13 connected in shunt thereto and a tuned secondary winding. The coupling between the said windings and the magnitude of the resistor are so chosen that the transformer passes a band of frequencies sufiiciently wide to give high fidelity.

The function of the second fidelity control tube is to decrease the effective coupling between the primary and secondary transformer windings during the reception of weak signals and to increase the effective coupling during the reception of strong signals, with respect to the effective coupling during reception of signals of average strength. Obviously, the result is increased selectivity during weak signal reception and increased fidelity during the reception of strong signals.

In order that this function may be accomplished, the grid of the second fidelity control tube is supplied with control potential directly from the plate circuit of the volume control tube 41, and the normal bias applied to the grid of the said fidelity control tube is such that it operates on the straight line portion of its characteristic curve. Such being the case, the impedance of the tube is approximately 10,000 ohms during the no-signal state and, as the bias on the grid becomes more and more negative in response to increased signal amplitude, the impedance rises to a higher and higher value thus effectively removing the shunt normally established around the primary winding of the output transformer across which the space current path in the tube is connected. The increased impedance of the tube, in response to increased signal amplitude, also increases the efiective coupling between the windings of the transformer, thus broadening its characteristic curve at the peak thereof and causing an increased energy transfer between the third and fourth IFA tubes. It should, of course, be understood that the eifect of the second fidelity control tube, upon the selectivity and fidelity of response of the system, adds to the effect of the first fidelity control tube.

In the event that it is desirable to reduce the expense of manufacturing a receiver according to my invention, some of the advantages thereof may still be retained if the input circuit of the tube 59 is divorced from the plate supply lead 5 to the tube l and manually operable means are provided for controlling the grid biasing potential ofthe said tube 59. Such means may take the form of a variable contact device associated with the main supply resistor 3| or any other 10 equivalent device.

Through variation of the grid potential of the tube 59, or grid potential of a plurality of similar tubes, a continuous variation in the selectivity characteristic of the receiver may be obtained. 15

Under certain circumstances, it is desirable that volume control be had without any change in the amplification characteristics of the several thermionic devices, such as is caused by alteration of the grid or other potentials applied 20,

thereto. It, accordingly, lies within the scope of my invention to dispense with grid potential control on the amplifier tubes and to provide a system wherein certain of the tubes are either transformer or impedance-coupled, as shown in 25. Fig. 1, and, further, to provide means, instead, for altering the energy transfer between the several tubes of the system in response to changes 7 in signal amplitude. A system so modified is shown in Figure 2 of the drawing.

Referring to Figure 2, a receiving system embodying a modified form of my invention com-- prises a plurality of intermediate frequency amplifying tubes 15, 11, and I9 and a second detector tube 8|, each of the tubes, preferably, be- 35 ing of the screen grid, equi-potential cathode type. The several tubes are inter-connected through coupling networks, each network comprising a tuned impedance 83 and a stopping condenser 85. 40

Further, each of the tubes may be provided with a self-biasing resistor 81, if desirable, or the grids thereof may, instead, be connected to appropriate points on a main anode supply resistor 83. 1

The source of signals at the intermediate frequency is not shown in the drawing, it being obvious that such signals may be derived from incoming radio signals in any customary and wellkno-wn manner.

Under normal conditions of no signal, or weak signal reception, it is desirable that the system shall be extremely selective and that the energy transfer between the successive tubes shall be a maximum. It is, further, desirable that, in the event the preceding stages of the complete system (not shown) be tuned to a strong signal, the overall gain in the system shall be reduced and the response characteristic be broadened.

I have, accordingly, provided a plurality of gain-control tubes 89, 9!, and 93, the space current paths in which are, respectively, connected in shunt to the output circuits of the first, second, and third intermediate frequency amplifying tubes. I

In order that the gain-control tubes shall exert no shunting action upon the tube circuits with which they are associated during the reception of weak signals, it is necessary that their respective impedances be maintained high. This, of course, may be accomplished by applying to the grids thereof a potential of approximately the plate current cut-oif value.

It is also desirable that the impedances of the gain-control tubes shall be reduced during the reception of strong signals, which reduction in 76 impedance may be accomplished through automatic variation of the grid potential applied thereto, in response to changes in signal amplitude.

I, accordingly, provide a master'gain-control tube having an input circuit constituted by a resistor 9i connected between the grid thereof and the main supply resistor 88 and an output circuit also constituted by a resistor 99, the latter resistor, preferably, being shunted by a condenser NH. The cathode of the master selectivity control tube is connected to a point on the anode supply resistor 88 sufficiently positive with respect to the point of grid connection that the said tube is biased to substantially the cut-off point.

It is, of course, to be understood that the normal bias on the tube 95 may be varied to meet different requirements. In other words, if the gaincontrol tubes are not to function until an incoming signal has reached a definite pre-determined value, the bias potential may be more negative than the cut-off potential.

In any event, it is necessary that the master gain control tube shall so function as to rectify incoming signals in order that the current in the output resistor thereof shall be a function of the amplitude of the said signals. To this end, a connection 5533 including a condenser I extends between the input circuit of the second detector tube 8i and the grid of the said master gain control tube whereby amplified incoming signals may be impressed thereon. The connection I93 may, alternatively, be extended to any other desired point in the system.

Obviously, from a consideration of the foregoin description, it will be apparent that increased signal strength results in an increased potential drop across the output resistor 99 which, if directly applied to the grids of the gain control tubes, would increase their impedances instead of reduce them, as desired. Accordingly, since it is more convenient that the cathodes of the selectivity control tubes shall be connected to the main supply resistor, as shown in the drawing, it is necessary to interpose, between them.

and the master gain control tube, means whereby the phase of the voltage appearing across the output resistor of the last named tube may be changed For this purpose, I prefer to utilize what might be termed an inversion tube ltl, the grid of which is directly connected to the plate of the master gain control tube and the output circuit of which includes a resistor Hi9 connected between the' anode thereof and the main supply resistor. The junction between the anode of the inversion tube and the resistor is connected to a conductor Ill common to the grids of the gain control tubes.

Accordingly, any change in potential across the output resistor 99 of the master gain control tube 95 is accompanied by a change in opposite sense across the resistor H39 in the output circuit of the inversion tube lill, and thegrids of the gain control tubes are thus given a more positive potential in response to an increase in the amplitude of an incoming signal. The last named tubes, therefore, exert a shunting action upon the output circuits of the several intermediate frequency amplifying tubes, the impedance of the gain control tubes decreasing with increase in signal amplitude.

The shunting affect broadens the response of the system and, at the same time, reduces the gain therein. A strong signal, therefore, is met by decreased gain accompanied by improved fidelity,

those skilled in the art to which it pertains.

while a weak signal finds the amplifier highly selective and capable of high amplification, the several enumerated functions being obtained without any change in the grid biasing potentials applied to the amplifying tubes from the resistors 5 81, whereby their characteristics remain unaltered. The advantages of my improved automatic volume, selectivity, and fidelity control system will be apparent, after a careful consideration of the foregoing description thereof. 10

Although I have selected certain embodiments of my invention for the purpose of explanation, many modifications thereof will be apparent to y invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In a signal receiving system, a plurality of amplifying devices, coupling means inter-com necting said devices in cascade, means for alter ing the selectivity of the system through at least one of said coupling means in response to a change in the amplitude of a signal impressed on said system and means connected with at least 25 one other of said coupling means for compensating losses in gain caused by operation of said second named means. i

2. In a signal receiving system, a plurality of amplifying devices, coupling means inter-connecting said devices in cascade, means for altering the selectivity of the system through at least one of said coupling means in response to a change in the sensitivity of the system and means connected with at least one other of said couplings 35 means for compensating losses in gain caused by operation of said second named means, said selectivity altering means including a first fidelity control device connected with said one of the coupling means for broadening the tuning of and 4 decreasing the energy transfer through said coupling means in response to increased average signal strength, and said gain compensating means including a second fidelity control device for increasing signal circuit coupling through said 45 other of said coupling means in response to increased average signal strength.

3. In a signal receiving system, a plurality of amplifying devices, coupling means inter-connecting said devices in cascade, means for automatically altering the gain of said system in response to a change inthe amplitude of an incoming signal, means for altering the fidelity characteristic and energy transfer through at least one of said coupling means, and means for alter- 55 ing the effective circuit coupling through another of said coupling means, all in response to the change in the average amplitude of an incoming signal.

4. In a signal receiving system, means for altering the gain therein in response to a change in the average amplitude of an incoming signal, means automatically responsive to the alteration in gain in effective signal circuit coupling in said system thereby to control the system for controlling the signal energy transfer therethrough and fidelity thereof, and a second fidelity control means responsive to changes in the average amplitude of an incoming signal, said fidelity control means being cooperative to increase the fidelity 70 characteristic of the system in response to increased average signal strength.

5. In combination, a plurality of electronic tubes connected in cascade through coupling devices to constitute an amplifier, means for impressing signals on said tubes, means responsive to changes in average signal amplitude, for varying the fidelity and gain in opposite sense through one of said coupling devices, and means responsive to changes in average signal amplitude for varying the fidelity and gain in the same sense through another of said coupling devices.

6. The invention set forth in claim 5, wherein the effectiveness of the coupling devices is altered through variation in the impedance of means connected in shunt relation thereto.

7. In a signal receiving system, means including a cascade connected electronic amplifier and a control circuit therefor for causing the gain in at least one of the amplifier coupling circuits to vary inversely and in another of the amplifier coupling circuits to vary directly with the amplitude of an incoming signal, said control circuit including means for causing the fidelity of response to vary inversely with the gain in one of said coupled circuits.

8. In a multi-stage amplifying system, means for causing the fidelity of response to vary directly with the amplitude of an incoming signal and means whereby the gain in one of said stages varies inversely with the gain in another of said stages, simultaneously with the alteration in the fidelity of response.

9. In a signal receiving system including a plurality of electronic amplifying devices, the combination of coupling means therefor arranged to connect two of said devices in cascade relation, said coupling means including two tuned coupled circuits, an electronic control device providing variable impedance means connected in parallel with one of said tuned circuits, and means for applying controlling potentials to said variable impedance means in a direction to cause the impedance to increase when the signal strength is increased, thereby to control the selectivity characteristic of the system and the gain through said couplmg device in the opposite sense one with respect to the other.

10. A thermionic amplifying system including a plurality of cascade connected electronic amolifier devices, and means for controlling the fidelity and selectivity characteristic of the system in response to changes in the average amplitude of signal currents transmitted therethrough, said means including a pair of signal circuit coupling devices, an electronic controlling device interconnected each with one of said coupling devices, and means for applying controlling potentials to said thermionic devices for increasing the fidelity characteristic of the system and decreasing the signal energy transfer through one of said coupling devices in response to an increased average signal amplitude, and for increasing the effective circuit coupling through another of said coupling devices in response to an increased average signal amplitude, whereby.

the gain in said system may be maintained substantially unaffected by changes in the fidelity and selectivity characteristics thereof 11. A signal amplifying system including a plurality of cascade connected electronic amplifying devices and a volume control means therefor responsive to changes in the average amplitude of an applied signal, characterized by the fact that the volume control means comprises variable impedance devices connected in shunt with certain of the interstage coupling means in the amplifying system at two difierent points to variably load the signal channel of the system, and means for applying controlling potentials to said variable impedance means in a direction to cause the impedance value of one of impedance means to increase when the signal strength is increased and the gain at each of said points to be controlled inversely with respect to the other.

12. The combination with an electronic signal amplifier including a plurality of electronic amplifier devices and coupling means connecting said devices in cascade relation to each other, of a plurality of control circuits for said amplifier, each of said circuits being connected with a diiierent one of said coupling means and including an electronic control device, means for applying biasing potentials to said control devices, means for varying said potentials for two of said devices inversely in response to changes in the average amplitude of signals transmitted through said amplifier, and means responsive to said inverse potential variations for varying the selectivity in the same sense and the gain in the opposite sense through two of said coupling means.

13. In a signal receiving system, the combination of means providing two tuned coupled signal circuits, an electronic control device providing a variable impedance across one of said circuits, and means for increasing the impedance of said control device in accordance with increases in the average amplitude of received signals.

14. In a radio receiving system, the combination of a plurality of electronic amplifier devices, coupling means between at least two of said devices comprising a pair of coupled tuned circuits, means including the space current path of an electric discharge tube providing a variable impedance in parallel with one of said tuned circuits, and means for increasing the impedance of said path in response to a received signal, thereby to vary the selectivity of said system through said coupling means inversely with the impedance of said means.

15. In a radio receiving system, the combination of a plurality of electronic amplifier devices, coupling means between at least two of said devices comprising a pair of coupled tuned circuits, means providing a signal controllable variable impedance in parallel with one of said tuned circuits, and means for increasing the effective value of said impedance in response to increases in the signal amplitude, thereby to vary the selectivity of said system through said coupling means inversely with the impedance of said variable means.

16. In a radio receiving system, the combination of a plurality of electronic amplifier devices, coupling means between at least two of said de vices comprising a pair of coupled tuned circuits, an electronic control device connected in parallel with one of said tuned circuits, and means for impressing control potentials on said control device in response to received signals in a direction to vary the selectivity of said system through said coupling means inversely with the impedance of said control device.

1'7. Ina radio receiving system, the combination of a plurality of electronic amplifier devices, coupling means between at least two of said devices comprising a pair of coupled tuned circuits, an electronic control device connected in parallel with one of said tuned circuits, and means for increasing the impedance of said control device in accordance with increases in the amplitude of a signal impressed upon said system.

18. In a radio receiving system, the combination of a plurality of electronic amplifying devices, automatic volume control means therefor, means providing two tuned coupling circuits between at least two of said electronic devices, electronic tube means providing a variable impedance across one, of said tuned circuits, and means for impressing controlling potentials from said automatic volume control means on said electronic tube to cause the impedance thereof to increase with increases on signal strength and thereby to vary inversely the selectivity and gain of the system through said coupling device.

19. In a radio receiving system, the combination of a plurality of electronic amplifier devices, automatic means for controlling the gain in said amplifier devices, coupling means between at least two of said devices, and manual means for varying the selectivity of said coupling means, said last named means including a variable impedance connected in parallel with one element of said coupling means.

20. In a radio receiving system, the combination of a plurality of electronic amplifier devices, automatic means for controlling the gain in said amplifier devices, coupling means between at least two of said devices, and means for varying the selectivity of said coupling means including an electronic control device and manual means for varying the impedance of said control device.

21. In a radio receiving system, the combination of a plurality of electronic amplifier devices, coupling means for said amplifier devices, signal controlled means for deriving control potentials varying in opposite sense, and means for utilizing said control potentials to vary the selectivity of at least two of said coupling means in the same sense.

22. In a radio receiving system, the combination of a plurality of electronic amplifier devices, coupling means for said amplifier devices, a pair of electronic control devices, means for applying controlling potentials to said devices in opposite sense in response to varie ions in the average signal amplitude, and means providing connections between each of said control devices and one of said coupling devices to provide a variable load thereon, said coupling devices including coupling elements responsive to variations in load to vary the fidelity characteristic of the system in the same sense in each of said coupling means.

23. In a radio receiving system, the combination of a plurality of electronic amplifier devices, coupling means for said amplifier devices, a pair of electronic control devices, means for applying controlling potentials to said devices in opposite sense in response to variations in the average signal amplitude, means providing a connection between each of said control devices and one of said coupling devices to provide a variable load thereon, said coupling devices including coupling elements responsive to variations in load to vary the fidelity characteristic of the system in the same sense in each of said coupling means, and one of said coupling means including a transformer having tuned coupled windings across one of which said loading means is connected, whereby the selectivity and gain through said last named coupling means may vary inversely with variations in loading.

24. In a radio receiving system, the combination of a plurality of electronic amplifier devices, automatic means for controlling the gain in said amplifier devices, means for varying the selectivity of said system through said-amplifier devices including electronic means for loading differing signal conveying circuits between the amplifier devices, means for derivingcontrolling potentials for said electronic means which vary in abizslzs coupled circuits, an electronic tube having its space current path substantially in parallel with one of said tuned circuits, automatic volume control means for said amplifier connected withsaid last named tube to supply controlling potentials thereto in a direction to cause the effective coupling between said circuits to decrease in response to a decrease in signal strength.

26. In a radio receiving system, the combina- 1 tion of a plurality of electronic amplifier devices,

automatic means for controlling the gain in said amplifier devices, coupling means between at least two of said devices, and automatic means varying the selectivity of said coupling means, said 20 last named means including an electronic amplifier device having a control electrode and having its space-path connected in parallel with one element of said coupling means.

27. In a radio receiving system, the combination of a plurality of electronic amplifier devices, automatic means for controlling the gain in said amplifier devices, coupling means between at least two of said devices, automatic means varying the selectivity of said coupling means, said last named means including an electronic amplifier device having a control electrode and having its spacepath connected in parallel with one element of said coupling means, and said control electrode being connected with said automatic gain con- 35 trolling means to receive a controlling potential therefrom.

28. In a radio receiving system, the combination of a plurality of electronic amplifier devices,

automatic means for controlling the gain in said 40 29. In a radio receiving system, the combination of a plurality of electronic signal amplifier devices, automatic means for controlling the gain in said amplifier devices, coupling means between at least two of said devices, and automatic means for varying the selectivity of said coupling means,

said last named means being responsive to changes in the anode current of at least one of said signal amplifier devices.

30. In a radio receiving system, the combinacoupling means for said amplifier devices, signal controllable means for deriving control potentials varying in opposite sense, said signal controllable means including an electronic amplifier device in tion of a plurality of electronic amplifier devices,

the signal amplifying channel of said system, and

means for utilizing said control potentials to vary the selectivity of at least two of said coupling means in the same sense.

31. In a radio receiving system, the combina- 7 tion of a plurality of electronic amplifier devices, coupling meansfor said amplifier devices, signal controllable means for deriving control potentials varying in opposite sense, said signal controllable means including an electronic amplifier device and a phase-changing electronic device coupled thereto, and means for utilizing said control potentials to vary the selectivity of at least two of said coupling means in the same sense.

32. In a radio receiving system, an electronic signal amplifier including an amplifier tube, an automatic volume control tube, a control tube for said amplifier coupled to said automatic vol-' ume control tube to receive controlling potentials therefrom, a second control tube for said amplifier coupled to said signal amplifier tube to receive controlling potentials therefrom, and means for coupling said control tubes to said amplifier to control the selectivity thereover in response to variations in said controlling potentials.

33. In a radio receiving system, the combination with electronic amplifier devices and coupling means between said devices, of controllable damping means for said coupling means, means for deriving controlling potentials proportional to the amplitude of the carrier wave of received signals, and means for simultaneously controlling the gain in said system by applying said controlling potentials simultaneously to the electronic amplifier devices and to the controllable damping means.

34. The combination with an electric signal amplifier, of means for variably loading a signal conveying circuit of said amplifier, means responsive to variations in signal amplitude for controlling the gain of said amplifier, said last named means including an impedance device providing a variable potential and an electronic amplifier tube providing a coupling means between said last named impedance and said variable load means.

35. In an electric signal amplifier, means providing an automatic volume. control potential therefor, means for reversing the phase of variations in said potential, variable loading means for a signal conveying circuit of said amplifier, said last named means being responsive to variations in a controlling potential, said loading means being connected to said phase reversing means to receive a controlling potential therefrom.

36. In an electric signal amplifier, the combination with a signal conveying circuit and an electronic amplifier, of means for deriving an automatic volume control potential for said amplifier, variable loading means for said circuit, and means including an electronic amplifier tube for reversing the phase of variations in said automatic volume control potential and for applying said reversed potential to said loading means to control the same.

3'7. In a signal amplifier, the combination with a pair of electronic amplifier devices and signal coupling means interconnecting said device, of 5 meansproviding variable electrical damping for said coupling means responsive to potential variations, automatic volume control means providing a signal variable potential, and means for utilizing said potential to simultaneously control the gain in at least one of said amplifier clevices and the damping of said coupling means.

38. In a radio receiving system, the combination of a plurality of electronic amplifier devices, coupling means for said amplifier devices, automatic volume control means for deriving control potential proportional to the amplitude of the carrier wave of. received signals, and means for utilizing said control potential to control simultaneously the signal gain in said system and damping of circuits connected with said coupling means.

39. In an electronic signal amplifier, the combination with a plurality of cascade connected electronic amplifier devices, of means for simultaneously changing an operating characteristic of certain of said electronic amplifier devices and the coupling between said devices, said means being responsive to variations in a controlling potential, signal responsive amplifier device for deriving potentials which vary in opposite sense in response to signal variations, and means for applying said potentials to said amplifier devices and to said coupling means.

40. In a radio receiving system, the combination of a plurality of electronic amplifier devices, coupling means for said amplifier devices, signal controllable means including separate electronic amplifier devices for deriving control potentials varying in opposite sense, and means for utilizing said control potentials to vary the selectivity of at least two of said coupling means in the same sense.

41. In a radio receiving system, the combination of a plurality of electronic amplifier devices, coupling means for said amplifier devices, signal controlled means for deriving control potentials varying in opposite sense, means for utilizing said control potentials to vary the selectivity of at least two of said coupling means in the same sense, and means providing a common source of operating potentials for the grid and anode circuits of said amplifier devices and selectivity controlling means.

GEORGE L. BEERS.

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