US2216582A - Automatic volume control with noise suppression - Google Patents

Description

Oct. l, 1940. L. E. BARTON 2,216,582

AUTOMATIC VOLUME CONTRL WIT NOISE SUPPRESSION Filed NOV. 3, 1932 '3 Sheets-Sheet 1 AUB/0 AMI? DE! VE E' ISIDETECTOE ott. 1, 1940. E E BA'RTQN 'I 2,216,582

AUTOIATIC VOLUME CONTROL WITH NOISE SUPPRESSION med Nov. s, 1932 :s sheets-sheet 2 ATTO/EWEK Oct. l, l940. l.. E. BARroN 2,215,582

I' AUTOHATIC VOLUME CONTROL WITH NOISE SUPPRESSION Filed NOV. 5) 1932 3 Sheets-Sheet 3 INVENTOR Loy EBarvn,

Patented Oct. 1, 1940 UNITED STATES i l nessi AUTOMATC VOLUME CONTROL WITH N @ISE SUPPRESSION Loy E.- Barton, Collingswood, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application November 3, 1932, Serial No. 640,946

34 Claims.

My invention relates to signal receiving apparatus, and it has particular relation to devices for preventing the response of such apparatus to signals of amplitude less than a predetermined value.

It has previously been proposed to provide signal receiving apparatus with automatic volurne control devices whereby the ultimate sound output is rendered substantially independent of fading and other phenomena which tend to cause the amplitude of an incoming signal to greatly vary. In the operation of receivers equipped with automatic volume control devices, however, some dissatisfaction has been experienced by reason of the fact that, during the operation of manually or automatically tuning the system from one desired station setting to another, intervening stations are received. Furthermore, during the tuning operation, there is always present, from a wide variety of sources, objectionable interference of the type generally designated as background noise.

It is, accordingly, an object of my present invention to provide means whereby a portion of l'. a radio receiver is rendered inoperative during the tuning operation.

Another object of my invention is to provide means whereby background noise shall be eliminated during the operation of tuning a signal receiving system from one desired station to another station.

Ano-ther object of my invention is to provide, in a system of the type described, means whereby automatic volume, or gain, control, as well as silent tuning, may be had without the necessity of using an extra thermionic tube.

A still further and more specific object of my invention is yto provide a novel thermionic tube, through the use of which the foregoing enumerated functions may be had.

The aforementioned objects and other objects appurtenant thereto, I prefer to accomplish through the use of a new and improved thermionic tube wherein, in addition to the usual f triode structure, is disposed one, or more, diode plates providing, with the cathode of the tube,

additional space current paths. I also provide a system of resistors and potential sources whereby the current traversing one, or more, of the :mj additional space current paths in the aforementioned tube gives rise to a potential, or potentials, proportional to the amplitude of an incoming carrier wave, and, in addition, I provide circuit connections whereby the said potential, or zijn potentials, may be utilized for both volume con- Ri l (Cl. Z50-20) trol purposes and-for the purpose of rendering the system unresponsive to background noise or signals below a predetermined amplitude during the operation of tuning from one desired station i.

but it will hereinafter be noted that, irrespective of the specific nature of the triode portion of my improved thermionic tube, one of the diode elements is utilized for automatic volume control.

rIhe novel features that I consider characteristic of my invention are yset forth in particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages, will best be understood from the following descrip-tion of a specific embodiment and certain variants thereof, when read in connection with the accompanying drawings wherein:

Fig. 1 is a diagrammatic view of a radio receiver of the superheterodyne type including a preferred embodiment of my invention,

Fig. 2 is a fragmentary diagrammatic view illustrating a modication of my invention,

Fig. 3 is a further fragmentary View of a radio receiver illustrating yet another modification of my invention,

Fig. 4 shows a modification of the circuit shown in Fig. 3.

Although, as will be obvious to those skilledv in the art, my invention is applicable to radio receivers of many different types, I have found it convenient to exemplify it in connection with a superheterodyne receiver. Referring specifically to Fig.. l of the drawings, a superheterodyne radio receiver is shown including a preferred embodiment of my invention and comprises a radio frequency amplifier tube I of the radio frequency pentode type having a tunable input circuit 3 connected to the control grid 5 thereof. A rst detector tube 1, of the same type, has its tunable input circuit 3 coupled to the output tunable circuit 5 of tube I.

An intermediate frequency amplifier tube 9, also of the pentode type, follows the first detector; a combined second detector, automatic `gain control, noise suppressor and audio frequency amplifier tube Il, constructed according to my invention, follows the tube 9. A driver tube i3 is coupled to the output of tube Il, and is followed by a plurality of audio frequency amplifier tubes I5 and I1 connected in push pull, the output circuit of which may be coupled in any desired manner to a loudspeaker I 9 or other indicating device.

A local oscillator is included in the system, and is conventionally indicated in the drawings by a rectangle 2. The oscillator is shown as having an output circuit 2 coupled to the input circuit 3 of the first detector tube l. Naturally, the oscillator in an actual receiver includes a thermionic tube having a tunable resonant circuit which is simultaneously tunable with the tunable resonant circuits of the radio amplifier and rst detector stages of the receiver. In order to simplify the drawing the specio connections of the said oscillator tube have been omitted; the unicontrol tuning mechanism also being omitted for the same reason.

As is usual in receivers of the superheterodyne type, the couplings between the radio freqeuncy amplifier I and the first detector 1, between the first detector and the intermediate frequency amplifier 9, as well as between the intermediate frequency amplifier and the second detector II, are of the band pass type. Such couplings are constituted by radio frequency transformer M1 and intermediate frequency transformers M2, and M3, respectively, each of the latter two having a tunable primary and a tunable secondary winding. The transformers M2 and 1W; are resonant to the operating intermediate frequency; the latter is kept constant in any desired manner throughout the tuning range of the receiver.

The second detector tube may be coupled to the driver tube I3 in any desired manner; I nd it expedient to utilize a coupling network so designed as to permit of compensated volume control. The network will hereinafter be referred to in more detail. As is customary in radio receivers of the so-called "all electric type, the cathode heating, grid biasing and anode potentials of the receiver tubes are supplied from a commercial alternating current supply line.

Specifically, the potential supply system I have found satisfactory includes a power transformer P having a plurality of secondary windings S1, S2, S3, and S4. The windings S2, and S1, respectively, supply cathode and plate potential to a full wave rectifying device R, while the last mentioned windings S3 and S4 supply cathode heating potential to the several tubes in the system. 'I'he rectifier R is provided with an output resistor, or potential dividing device R1, and in the negative connection thereof I find it expedient to dispose the field winding L1 of the loud speaker of a sound producing device for a purpose which will later be referred to.

Plate potential to all ofthe amplifying tubes in the system is supplied from the positive end of the output resistor R1 over a common conductor 6. Screen grid potential is supplied to the radio frequency amplifier I, the first detector T, and the intermediate frequency amplier 9 from an intermediate point a. on the output resistor R1 over a common conductor 6. The multiple duty tube II comprises a cathode I2, a control grid II', an anode I4, and a plurality of diode anode elements I6 and I8.

As hereinbefore pointed out, it is one of the objects of my invention to provide a receiver wherein tuning is silent. In order that this may be accomplished, I utilize one of the diode elements as a detector, and supply the said element with a controllable bias potential of such magnitude that incoming signals supplied thereto from the intermediate frequency amplifier are not rectiiied unless the said signals exceed a definite predetermined amplitude. The manner in which the controllable bias is supplied to the diode element is as follows: The cathode I2 of the tube II is connected to the most negative portion of the potential supply system through a cathode resistor 2U.

The grid Il of the said tube is connected through an adjustable contact device 2I to a point on a resistor 22 which, in turn, is shunted across between the said most negative portion of the potential supply system and a point b on the output resistor R1 at a positive potential with respect to ground. The path to the device 2| also includes the resistors 23, 24. Adjusting the movable contact element 2| permits the grid I I' of the tube II to be supplied with a potential which is either positive or negative with respect to the grounded point of the said output resistor.

In the operation of the system, and assuming that no signals are being impressed upon the diode element I 6 of the tube I I, the movable contact device 2I is adjusted along the resistor 22 until the fall in potential along the self-bias resistor 2D is substantially balanced by the rise in potential across the loud speaker eld winding L1, whereby the grid II of the tube II and the diode element I6 are maintained at zero potential with respect to the cathode, or at a potential which is slightly negative. The amount of the negative potential is, of course, determined by the position of the contact element 2l, and adjustment of this element may be so made that the diode element does not function until the said negative potential is overcome by an incoming signal having a definite predetermined amplitude. This feature enables the system to be adjusted for silent tuning.

Assuming now that the incoming signal eX- ceeds the predetermined minimum amplitude, it is applied between the diode element I6 and the cathode I2 of tube II through grid leak resistor 24 and condenser 24. The control grid II of the tube is connected to the high potential side of the grid leak 24 through resistor 23. It will be noted that the intermediate frequency voltage applied to the control grid will be very small, and that the resistor 23 is inserted to further reduce the signal at the intermediate frequency. It should also be apparent that the bias for the control grid is obtained from the direct current voltage across the grid leak 24 which, in turn, is proportional to the carrier of the signal.

The plate current of the triode portion of the tube is limited by a resistance 25, (or a series combination of plate, reactor and resistance) in series with the plate supply conductor 6, and by the cathode resistor 20 so that the voltage across the said cathode resistance is a maximum at zero signal and decreases as the signal increases.

It will also be apparent that the voltage across the cathode resistance 20 and the loud speaker eld L1 are in the same direction, and that normally the voltage across the said resistor 20 is larger than the voltage across the eld in the absence of signals. In this condition, therefore, the diode plate I6 may be negative with respect tothe cathode of the tube depending upon the adjustment of resistance 22. 'Ihe second diode plate I8 is negative in the last named condition,

and is connected over a conductor 26 and a plurality of resistors 21, 28, 29 to ground.

In the no signal condition the potential drop across the cathode resistor 20 is greater than the rise in potential across the lo-ud speaker field L1 and, accordingly, a negative potential is supplied to the said secon-d diode element I8. For automatic volume control purposes, the grids of the radio frequency amplifier I, the first detector 'I and the intermediate frequency amplifier S are connected to appropriate points on the aforesaid resistors included between the second diode plate I8 and ground. Thus, the grid of tube I is connected to one side of resistor 28; the grids of tubes 1, II are connecte-d through lead 30 to a point intermediate resistors 28, 29. This permits the bias applied to the grid of tube I to be greater than that applied to tubes 'I and 9 to prevent overloading on the side of a strong carrier. Obviously, therefore, during the no signal condition the negative bias applied to the said tubes is a minimum, and is determined solely by the potential drop across the self-bias resistor 3| connected into the cathode return circuit of tubes I and 9.

As a signal is applied to the diode plate I6 its rectification causes a negative potential to be developed across the grid leak 24, and, since the control grid II' of the tube is connected to the said grid leak as hereinbefore explained, it becomes more negative, thus causing the plate current of the triode section of the tube II to decrease. The decrease in current through the cathode resistor 20 permits the second diode element I8 to become more positive With respect to cathode l2 by the amount of change in the difference of the voltage across the loudspeaker field and the cathode resistor 20. If the input signal is sufficiently large, the decreased voltage across resistor 20 causes the diode anode I8 to become positive with respect to cathode I2 by virtue of the fact that cathode v I2 becomes negative with respect to ground, Therefore, current ows from ground to the diode anode I8 through resistors 29, 28 and 21, the voltage across these resistors being essentially equal to ground and the potential of cathode I2 because the resistance of the diode anode I8 is relatively small. The direction of this current is from ground up through the resistors 29, 28, 21, included between ground and the diode plate, causing a potential drop in the proper direction to supply bias to the radio frequency amplifier I, the rst detector 1, and the intermediate frequency amplier 9 for automatic volume control purposes. Obviously, the amount of current taken by the second diode element I8 increases as the signal increases in amplitude, and thus the increased signal is caused to be met by tubes the gain in which has been decreased.

In general, the voltage across the cathode resistor 2! during the no signal condition should be about 30 to 50 volts higher than the voltage across the loud speaker winding. This voltage determines the extent to which the automatic volume control action is delayed. The signal applied to the first diode element I5 may cause a reduction in voltage in the said cathode resistor 20 to approximately 60% of the initial voltage without serious distortion of the audio signal. In this connection, attention is called to the fact that there will be no automatic volume control until the voltage across the cathode resistor 20` is approximately equal to the voltage across the loud speaker field, so that a voltage for automatic volume control of 60 to '15 volts may be obtained without overloading the detector I I, if the voltage across the loud speaker field is about 1'10 volts and the plate supply for the receiver is about 230 volts.

The maximum voltage available for automatic volume control depends upon the available voltage across the speaker and resistor 20. Referring again to the action of the second detector tube l I, it should be noted that the audio voltage, due to the rectification of the signal by the rst diode element IB, is applied to the control grid II', whereby the said tube functions not only as a detector, but also as an audio frequency amplier. The noise suppression, or silent tuning, is obtained by adjustment of the contact device 2I associated with the resistor 22 which shunts a portion of the rectifier output resistor R1 and the loud speaker field winding. Naturally, if the contact element is moved downward toward the negative end of the shunting resistor, a signal of greater amplitude or noise of greater amplitude is required to overcome the negative bias applied toV the first diode element I6. In locations where interstation noise is not objectionable, the diode plate I6 may be maintained at substantially zero potential by proper adjustment of the contact element. It should be .noted that if the diode anode I5 is made negative with respect to the cathode by the adjustable tap 2 I, a signal slightly larger than this value is required to overcome the bias to cause some detection. The negative. potential to grid Il increases due to detection which automatically reduces the cathode potential withrespect to the point 2 I, thereby removing the negative potential on the diode anode I6 and thus permitting normal detection.

In order that a further control of the sensitivity of the system may be had, I prefer to supply normal bias to the radio frequency amplier and the intermediate frequency amplifier through a variable self-bias resistor 3l which is connected by leads 32, 33 between the cathodes of the said tubes and ground. Through proper adjusting of the said variable resistor, since in the no signal condition no bias is supplied from the circuit of the second diode plate I8, the normal bias on the said tubes may be adjusted to the desired point. l

The resistor 25 is by-passed with the condenser 311, and the audio voltage is obtained from the resistor 25 (and/or choke) in the plate circuit of tube Il through resistor 35 and condenser 36 to the potentiometer 31. The network, including the series condenser-resistor paths X, Y, Z, associated with the potentiometer 31, or the audio volume control, are used to obtain the desired compensation for varying volume levels and also tone control. 39 are used as a hum filter, if such is necessary. The network between tubes II and I3 need not be described in any further detail, since it is not a part of they present invention. The .amplier tubes I5 and I1 are arranged in push-pull, and need only be described as furnishing an amplifier of the class B push-pull type operating with zero grid bias. This arrangement has been described and claimed by me in a co-pending application Serial No. 586,874, filed January 15, 1932, granted June 15, 1937 as U. S. Pat. 2,084,180,

and is also described in the I. R. E. for July,

The tube I I is of the type known as an RCA-55, or a duplex-diode triode. The diode elements I6, I8 are disposed around an extreme portion of the cathode sleeve. vThe cathode is common for The resistor 38 and condenser the diode elements and the triode grid and plate. However, the diode anodes I6, I8 function independently of the triode elements. That is, the diode anodes I6 and I 8 are outside the electron system between cathode I2, grid II and anode I4. Further details of the construction of this tube will be found in a co-pending application of T. M. Shi-ader application Serial No. 622,140, filed July 12, 1932, granted Oct. 27, 1936 as U. S. Pat. 2,058,834.

In Fig. 2 there is'shown a modied form of the automatic volume control and noise suppressor arrangement of Fig 1. The combined second detector, automatic volume control, noise Suppressor tube is designated by the numeral 40. This tube is of the co-planar grid type with a diode anode, indicated as D1.

The grid 4I is connected to the one side of the tuned secondary winding of the transformer M3, in the same manner as the diode element I6 in the case of tube II of Fig. 1. The grid 4I is connected to the other grid 4I, and to the potentiometer R1 through a path which includes resistor 43 having a value of about 2 megohms, and a resistor 44 having a magnitude of about 20,000 ohms, a condenser 45 being connected between the junction of resistors 43 and 44 and the cathode of tube 40. It should be noted that the resistor 43 may be connected to the center of the secondary of coupling transformer M3 without altering the operation of the grids.

The cathode of tube'llll is connected to the -B side of a power supply system through a resistor 46 which functions in the same manner as resistor 20 in Fig. 1. The main anode 47 of tube 40 is connected to the +B side of a power supply system through a network 48, tuned to the second harmonic, the primary winding 49 of the audio frequency coupling transformer M4, and lead 50. The condenser 5I connects the low potential side of the winding 49 to the cathode of tube 40. The tuned circuit 48 increases the sensitivity of the tube 40 slightly but may be omitted.

The preceding intermediate frequency amplifier tube 9 has its cathode connected to the -B side of the power supply system through a path which includes the resistor 52, and the loud speaker eld winding 53, the junction of resistor 52 and field winding 53 being connected to the low potential side of the tuned input circuit of tube 9 through agrounded resistor 54 having a value of about 0.5 megohm. The resistor 55 is' connected between the junction of resistor 52 and the winding 53 and the anode lead to tube 9, one side of the potentiometer resistor R1 being connected to an intermediate point of the resistor 55. The diode anode D1 of tube 40 is connected to the low potential side of the grid circuit of tube 9 through a path, which includes lead 56 and resistor 51 in order to cause resistor 54 to feed automatic volume control voltage to tube 9.

The co-planar grid tube 40 is a tube wherein the grids 4I and 42 are concentrically wound in the same cylindrical surface. The diode anode D1 is disposed outside the main electron stream from the cathode to the anode 41, and therefore provides a diode independent of the co-planar grid triode. The circuit of diode anode D1 provides delayed automatic volume control action. Potentiometer R1 is so adjusted that in the absence of signals the grid-cathode bias is zero. The voltage across the resistor 46 decreases with signal because of the negative potential across 43 which is proportional to the signal and, until this voltage decreases to a certain predetermined value, say 160 volts from 190 volts, the bias for the intermediate frequency tube 9 will be normal. When such predetermined voltage has been reached, current begins to ow through the resistor 54 due to the potential across resistor 46 having become less than that across eld winding 53 so that anode D1 has become positive relative to the cathode of tube 40. Further increase in signal causes a decrease in voltage at resistor 46, and this increases the bias on tube 9. The arrangement shown in Fig. 2, also, includes noise suppression so that most, or all, noise when tuning between stations is automatically suppressed. The potentiometer R1 can be so adjusted that the tube 40 will have a negative bias on the grids 4I and 42, thereby preventing detection until a carrier of a predetermined amplitude is received. Signal detection causes the voltage across 46 to decrease, to say 160 volts, which removes the negative bias so that the grids 4I and 42 may detect in a normal manner. Further decrease in voltage across 46 automatically controls the sensitivity of the receiver by applying the further decrease as bias to the tube 9 through circuit 54, 51, 56 and the diode D1. Ihe grids 4I and 42 will become positive but the actual positive potential will be very small because of the high resistance 43. The slight positive potential will not interfere with detection.

In Fig. 3 there is shown a modification of the automatic volume lcontrol, delay and noise suppressor circuits of tube II in Fig. 1. The 55 type tube II is used for the second detector, automatic volume control and noise suppression functions, as in the case of Fig. 1. Referring to Fig. 3, the input intermediate frequencyk signal is applied to the diode anode D1 with the condenser and leak arrangement C1-R4. Contacts S1 are insulated from the contact arm S2 but are so mechanically connected that the contacts are closed when Sz is at extreme right. It will be noted that when the sensitivity control S2 is at the extreme right hand position, the sensitivity is maximum, and the switch contacts S1 are caused to be connected together by the movable arm Sz, so that the diode element D1 returns directly to the indirectly heated cathode sleeve. The tube II in Fig, 3 has been shown in greater constructional detail than in the case of Fig. 1 so as to show the positioning of the control grid and main anode, as well as the positioning of the auxiliary anodes D'1 and D2 with respect to the common cathode sleeve I2'.

When the arm S2 is in the extreme right the controlling shaft will also cause the switch contacts S1 to be closed as described above, and the bias on the element D1 is zero as well as on the grid II if the input signal is zero. The plate current for the tube I I ows through resistor R1, and returns to the negative plate potential through resistor R2 which is in the cathode lead of tube II. The voltage drop across resistor R2 is somewhat higher than the voltage across the loud speaker coil L3. The resistor R1 is used as a plate coupling resistor for the audio signal, and the condenser C5 by-passes the audio signal around resistor R2, and also lters out any hum that may exist in the plate supply to tube II.

Under no signal conditons, and with the arm S2 in extreme right position so that the two contacts S1 are closed, there is a negative potential on the diode element D2 through the biasing resistor R10. Therefore, there is no current flowing through the resistor R1o, so that the bias on the radio frequency and intermediate frequency systems is the minimum or fixed value. As a signal is applied to the element D1, the rectiiication causes a negative potential to be generated across resistor R4, and this in turn causes the plate current of the triode section of tube II to decrease. This decrease in current through resistor R2 results in a lower voltage drop across the latter, so that as the signal increases, the voltage across resistor R2 will become less than the voltage across the speaker iield winding L3. Under these conditions, the diode element D2 will become positive by the amount of the difference in voltage across resistor R2 and the iield I provided here, with regard to the delay action, a

rectifier system for producing audio and direct current components from the signal energy, a triode amplifier for amplifying both components, and an additional device of asymmetric conductivity for utilizing the amplified direct current component for delaying the automatic volume control action until the signal energy rises above a predetermined threshold value.

In general, the voltage across resistor R2, with no signal, should be about to 50 volts higher than the voltage across the winding L3. The signal applied to the diode element D1 may cause a reduction in the voltage across resistor R2 to approximately 60% of the initial voltage without serious distortion of the audio signal. It Will be noted that there will be no automatic volume control action until the voltage across resistor R2 is approximately the voltage across the winding L3 so that a net voltage for automatic volume control of 60 to '75 volts should be obtained without overloading the detector tube II. The audio voltage due to modulation will be applied to the grid II' through the resistor R5, and will be transmitted to the audio system through the plate resistor Ri and the coupling capacitor Cs. The resistor Re is used to reduce the intermediate frequency energy to the grid II, but will not affect the audio frequencies appreciably.

The effective circuit which resultswhen the arm S2 is in contact with contacts S1 may be had by referring to Fig. 4. This circuit will be the same as Fig. 3, except that the switch contacts Si, the leads connecting Si, the resistor R5, and the .condenser C2 should be omitted from the circuit. The low potential end of R4 will connect to the cathode of tube II to complete the changed circuit.

The noise suppression function is obtained by adjusting the potentiometer Ra slightly to the left, which opens the switch S1. In other words, when the arm S2 is moved to the left along the potentiometer resistor Rs, the two contacts of switch S1 are open, or disconnected, and the noise suppression function is restored. With this setting, that is the arm S2 moved slightly to negative potential amounts to approximately 8 volts, so that an incoming signal below this value will not be detected. Therefore, no noise will appear at the loud speaker.

If the noise level is such as to over-ride the suppressor, or negative diode, potential, then sensitivity may be reduced (by moving the arm S2 still further to the left) by increasing the normal negative bias on the grids of the control tubes thus making the overall amplication less so that the noise will not over-ride the negative potential on the diode element D'1. If this procedure is carried far enough it is obvious that no station .can be received, so that the range of the sensitivity control should be limited to such a value that stations with high eld strength can be received at the minimum sensitivity. This latter minimum point of sensitivity will then represent the extreme left position of the arm S2 on the potentiometer resistor Rs.

The principal advantages of the system shown in Fig. 3, as well as that shown in Fig. 1, reside in the fact that the detector, delayed automatic volume control and noise control functions are performed by only one tube. The audio output of the detector is approximately 50 volts for modulation before it overloads if the necessary intermediate frequency voltage is applied to the detector. This relatively high audio voltage permits the use of a compensated volume .control. The voltage for the automatic volume control is also more dependable because it depends upon a change in plate current of the detector and does not depend directly upon power from the intermediate frequency system. n

The noise control'feature providesa means for using a sensitivity control with a negative potential on the diode detector. potential on the diode eliminates the noise applied to the detector below a definite voltage, and the sensitivityv control permits an adjustment of noise level to the detector. An ordinary, sensitivity control in some receivers can be used as a volume control, but in the above system an adjustment of the sensitivity control either causes the'signal to disappear or to be receivednor` mally with a very limited range in which the signal is badly distorted. The result is that the user would not attempt to use the noiseplevel or sensitivity control as a volume control.

The circuit shown in Fig. 3 normally supplies audio Voltage through the coupling capacitor C6 to a high resistance potentiometer arrangement for compensated volume control, which potentiometer may be connected directly to the grid of an audio frequency driver tube. This latter volume control arrangement is shown in Fig. 1 between the tubes II and I3. rIThis is a satisfactory arrangement when the load in the plate circuit of the tube I I is very light, or has a high resistance. However, it is desirable at times to connect a transformer M6 to the plate circuit of the detector tube II sothat a push-pull output system, of the type shown in Fig. 1 bytubes I5 and I'I, .can be driven directly. In general, the latter arrangement means a relatively low resistance in the plate circuit of tube II so that it is not desirable to `use the resistance-condenser coupling network shown in Fig. 3.

The circuit arrangement shown in Fig. 4is designed to eliminate the plate load difliculty referred to in the preceding paragraph, and yet retain most of the desirable features of the circuit shown in Fig. 3.v The principal feature of the modification in Fig. 4 is the relatively low leak resistance R4, having a value of 0.1 megohm,

The negative lis to'y

with the high resistance audio volumecontrol P2, the resistor R of the manual volume control P2 having a value of about 1 megohm. The function of the manual volume control is similar to the compensated volume control in Fig. 1. It will be noted that the bias for the triode action of tube Il is the voltage across the resistor R4 so that the system for automatic volume control, detection and noise control as used in Fig. 3 may be employed here also. The resistor Re may be omitted if desired.

While I have indicated and described several systems for carrying my invention into eiiect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention as set forth in the appended claims.

What I claim is:

1. In combination, with a high frequency amplier whose gain is to be controlled in such a manner that the output of the amplifier is maintained at a substantially uniform level, a rectifier including a source of electrons and a cold electrode coupled to the amplifier output, means connected to the cold electrode of the rectier for maintaining the cold electrode negative with respect to the source of electrons when signals to be amplified are impressed upon the controlled amplifier input, an amplifier including a source of electrons and at least two cold electrodes, one of the two cold electrodes being connected to a point on said means, and the other cold electrode being connected to the source of electrons of the amplifier, a delay space discharge device electrically connected to the source of electrons of said amplifier, and an automatic volume control resistor connected between a cold electrode of the delay device and the high frequency amplifier.

2. In combination, an amplifier to be controlled as to the gain thereof, a rectifier, a second amplifier, means for impressing the rectifier output upon the second amplifier input, a device of asymmetric conductivity, means for impressing the second amplifier ouput on said device whereby the output of the second amplifier produces negligible effect in the output of said device until a desired threshold value is attained, and a direct current voltage connection between the output of said device and said controlled amplifier, the gain of said controlled amplifier being controlled from said device only after said threshold value is reached.

3. In combination, an amplifier to be controlled as to the gain thereof, a rectifier, a second amplifier, means for impressing the rectifier output upon the second amplifier input, a diode device, means for impressing the second `amplifier output on said device whereby the output of the second amplifier produces negligible effect in the output of said device until a desired threshold value is attained, and a direct current voltage connection between the output of said device and said controlled amplifier, the gain of said controlled amplifier being controlled from said device only after said threshold value is reached.

4. In combination, an amplifier to be controlled as to the gain thereof, a rectifier, a second amplifier, means for impressing the rectifier output upon the second amplifier input, a device of asymmetric conductivity, means for impressing the second amplifier output on said device whereby the output of the second amplifier produces negligible effect in the output of said device until a desired threshold value is attained, and a direct current voltage connection between the output of said device and said controlled amplifier, the gain of said controlled amplifier being controlled from said device only after said threshold value is reached, said second ampli; fier comprising an electron discharge tube including a cathode, control grid and anode, and said device consisting of an auxiliary anode disposed adjacent said cathode outside the electron stream between the cathode and the first said anode.

5. In combination, an amplifier to be controlled as to the gain thereof, a rectifier, a second amplifier, means for impressing the rectifier output upon the second amplifier input, a device of asymmetric conductivity, means for impressing the second amplifier output on said device whereby the output of the second amplifier produces negligible effect in the output of said device until a desired threshold value is attained, and a direct current voltage connection between the output of said device and said controlled amplifier', the gain of said controlled amplifier being controlled from said device only after said threshold value is reached, said second amplifier comprising an electron discharge tube including a cathode, control grid and anode, and said device consisting of an auxiliary anode disposed adjacent said cathode outside the electron stream between the cathode and the first said anode and said rectifier' comprising an additional auxiliary anode disposed adjacent said cathode outside said electron stream.

6. An automatic volume control arrangement for a radio receiver, which receiver includes a high frequency amplifier and a detector, said detector' including an electron discharge tube provided with a cathode, at least one control grid and at least one anode, a resistor in the cathode circuit of said detector tube, at least one auxiliary cold electrode in said detector tube, a direct current voltage connection between said auxiliary electrode and said amplifier for controlling the `gain of the latter, the voltage across said cathode resistor being of a magnitude exceeding the bias requirement for the detector.

7. An automatic volume control arrangement for a radio receiver, which receiver includes a high frequency amplifier and a detector, said detector including an electron discharge tube provided with a cathode, at least one control grid and at least one anode, a resistor in the cathode circuit of said detector tube, at least one auxiliary cold electrode in said detector tube, a direct current voltage connection between said auxiliary electrode and said amplifier for controlling the gain of the latter, the voltage across said cathode resistor being of a magnitude eX- ceeding the bias requirement for the detector, a second auxiliary cold electrode Within said detector tube, said second auxiliary electrode being connected to the output of said amplifier whereby it cooperates with a portion of said detector tube cathode to rectify signals supplied to the detector, means for connecting said control grid to a point on the detector input circuit whereby a wide range of voltage variation across said cathode resistor is secured.

8. An automatic volume control arrangement for a radio receiver, which receiver includes a high frequency amplifier and a detector, said detector including an electron discharge tube provided With a cathode, at least one control grid and at least one anode, a resistorin'the cathode circuit 0f said vdetector tube, at least one auxiliary cold electrode in said detector tube, a direct current voltage connection between said auxiliary electrode and said amplifier for controlling the gain of the latter, the voltage across said cathode resistor being of a magnitude eX- ceeding the bias requirement forI the detector and an additional control grid coplanarly arranged with respect to the rst control grid connected to a signal potential point on the detector input circuit which is out of phase with the point on the said input circuit to which the said first grid is connected.

9. In combination with ahigh frequency amplier stage whose gain is to be controlled, a tube provided with at least a cathode, control grid, and anode, and a pair of .auxiliary anodes positioned outside the electron stream between the cathode and said anode, a signal input circuit coupled between one of said auxiliary elecitrodes and the cathode, said signal input circuit being additionally coupled to the output of said amplifier, means for coupling said tube anode to a low frequency amplier', a direct current voltage connection between said control grid and said one auxiliary electrode, a direct current voltage connection between the other auxiliary electrode and said first amplifier, a resistive path in the cathode circuit of said tube, and an adjustable connection between said direct current voltage connection to said second auxiliary electrode and said resistive path.

10. In a superheterodyne radio receiver including an intermediate frequency amplifier, a second detector tube including a triode section and at least one independent diode section, an audio amplifier network connected tothe output electrodes of the triode section, a signal input circuit connected to the diode section to provide a rectication network, and a biasing impedance in the cathode circuit of the triode section connected to the said diode section for rendering the latter inoperative when signals of less than a predetermined amplitude are impressed on said input circuit, an auxiliary electrode in said tube pro- 7 provided with a cathode, a grid, an anode, and at viding a second independent diode section, and a direct current voltage connection between the auxiliary electrode and a gain control electrode of the intermediate frequency ampliiier.

ll'. In a superheterodyne radio receiver .including an intermediate frequency amplifier, a second detector tube including a triode section and at least one independent diode section, an audio amplifier network connected to the output electrodes of the triode section, a signal input circuit operative when signals of less than a predetermined amplitude are impressed on said input circuit, an adjustable audio volume connection between the grid of said triode section and apoint on said rectication network, and additional means for frequency compensating the said connection for different volume levels.

12. In a receiver of the type including at least one high frequency amplifier having a resonant input circuit, a detector stage including a tube least two cold electrodes adjacent said cathode but substantially unaffected by said grid, a signal circuit coupled to one of the cold electrodes and the cathode to produce rectified signal cur-v to the amplifier, a connection from the cathode to a point more negative than ground, and a resistance in said connection which is traversed by the anode current whereby the potential of cathode with respect to ground is positive in the absence of signals but becomes negative in the presence of strong signals.

13. In a receiver of the type including at least one high frequency amplier having a resonant input circuit, a detector stage including a tube provided with a cathode, a grid, an anode, and at least two cold electrodes adjacent said cathode but substantially unaffected by said grid, a signal circuit coupled to one of the cold electrodes and the cathode to produce rectified signal current, an impedance'which is high for both direct and audio currents connected between said one electrode and cathode to be traversed by said rectified signal current, means to impress between the grid and cathode voltage derived from said rectified current flowing through said impedance whereby the direct current component is decreased in proportion lto increasing signals, a direct connection from the other cold electrode to the amplifier, a connection from the cathode to a point more negative th-an ground, and a resistance in saidr connection which is traversed by the anode current whereby the potential of cathode with respect to ground is positive in the absence of signals but becomes negative in the presence of strong signals, means. for selecting at will a desired potential difference between the rectifier cold electrode and the cathode.

14. In combination with an amplier, rectier means for deriving a direct current proportional to an incoming signal, a space current device including an anode and a cathode, means for normallymaintaining said anode negative with respect to said cathode, and means whereby the said direct current is' utilized to cause a reversal of the polarity of said electrodes, with consequent flow of space current.

15. In a receiver of the type including at least one high frequency amplier having a resonant input circuit, a detector stage including a .tube provided with a cathode, a grid, an anode, and at least two cold electrodes adjacent said cathode bult substantially unaiected by said grid, a signal circuit coupled to one of the cold electrodes and the cathode to produce rectified signal current, an impedance which is high for both direct andV audio currents connecte-d between said one electrode and cathode to be traversed by said rectified signal current, means to impress between the grid and cathode voltage derived from sistance in said connection which is traversed by` thel anode current whereby the potential of cathode` with respect to ground is positive in the absence of signals but becomes negative in the presenceof strong 'signals and means for biasing the second cold electrode more negative than ground by an adjustable amount whereby current will not flow from the cathode to the second electrode until the cathode is more negative.

16. In a radio receiver, a radio frequency amplifier, a multiple function tube including a diode signal rectifier and an amplifier, circuit elements connecting said rectifier between said radio amplier and said second amplifier, means including a second diode for controlling the gain of said radio amplifier, and means for automatically suppressing the transmission of rectified signals by said tube when the radio frequency voltage impressed on said rectifier falls below a predetermined value. i

17. In a radio receiver, a radio frequency ampliiier, a multiple function tube including a diode signal rectifier and -an amplifier, circuit elements connecting said rectifier between said radio amplifier and said second amplier, means including a second diode disposed in said tube for controlling the gain of said radio amplifier, and means for automatically suppressing the transmission of rectified signals by said tube when the radio frequency voltage impressed on said rectifier falls below a predetermined value.

18. A multiple duty tube including an evacuated envelope, a cathode, a main anode, and a pair of co-planarly wound grids disposed within the envelope, said grids being arranged within the electron stream between the cathode and anode, and an auxiliary anode, of a relatively smaller area than said main anode, disposed adjacent said cathode outside said stream, the electron stream between said cathode and auxiliary anode being unobstructed by any electrode and independent of the said first stream, means for connecting the auxiliary anode and cathode to provide a diode rectifier circuit, and additional means for connecting the said grids to opposite sides of a signal input circuit.

19. In a radio receiver provided with a tube having a diode section and an electronic section including at least two cold electrodes and the cathode of said diode section, a signal input circuit connected to said diode section and providing a rectification network, a source of signal energy, means for connecting one of said cold electrodes to a point of alternating current potential in said network, and an auxiliary cold electrode disposed adjacent said cathode providing a second diode section, and a gain control connection between the auxiliary electrode and said signal source.

20. In a radio receiver, the combination with a tube having an anode, a control grid, plate and cathode, of a radio frequency amplifier, means cooperating with said anode and cathode to form a diode detector working out of said amplifier, means for automatically controlling the gain of said radio frequency amplifier, circuit elements for impressing upon said control grid an audio frequency Voltage developed by said diode detector, an audio frequency load in the plate circuit of said tube, means establishing a bias voltage between cathode and another tube ele ment to suppress the transmission of audio frequency currents by said tube, and means operable automatically when the received radio frequency voltage rises above a critical level to reduce the bias voltage to permit normal transmission by said tube.

21. The invention as set forth in claim 20, wherein said means for automatically controlling the gain of said amplifier includes a second anode within said tube and cooperating with said cathode to form a diode rectifier.

22. In combination with an amplifier of modulated high frequency carrier energy, a detector system comprising an electron discharge tube provided with a cathode, a plate and at least one control grid disposed in the electron stream between the cathode and plate, a resonant input circuit connected between the grid and cathode, at least two resistors connected in series with each other and connecting the grid and cathode. one of said resistors nearest the cathode being disposed in the space current path of the tube for developing a detection suppression bias for said grid in the absence of carrier energy above a predetermined intensity level, the said grid having impressed thereon direct current voltage developed across said other resistor when said energy increases above said level whereby the space current fiow through the said one resistor is reduced.

23. A radio receiver comprising an amplifier with potentially operated gain control means, a detector-amplifier-governor comprising a cathode, an anode, a grid and two auxiliary anodes arranged to receive electrons from the cathode without interaction with electrons fiowing to the other electrodes, a signal rectifier circuit comprising the cathode and an auxiliary anode coupled to an output circuit of the amplifier and to the grid, and an automatic gain control circuit comprising a potential source, the cathode, the second auxiliary anode and a connection to the gain control means and a manually operated sensitivity control for said first named amplifier.

24. In combination, a source of potential, a radio frequency amplifier with potentially operative gain control means, an electron tube having a hot cathode and a plurality of cold electrodes arranged to receive electrons from the cathode without interaction with electrons flowing to the other electrodes, a rectifier circuit comprising the cathode and a cold electrode electronically related to the cathode only coupled to an output point in the amplifier, an amplifier circuit comprising the source of potential, the cathode and cold electrodes coupled to the rectifier circuit and an automatic gain control circuit comprising the source of potential, an impedance, the cathode, a cold electrode electronically related to the cathode only and the gain control means.

25. In combination in carrier wave receiving apparatus, a source of electrical energy with potential taps, a carrier frequency amplifier with manual and automatic gain control means, an electron tube having an amplifier section and two diode sections, a rectifier circuit including one diode section coupled to the output of the carrier frequency amplifier, an amplifier circuit including the amplifier section coupled to the rectifier circuit and energized from taps on the source of energy, and an auttomatic volume control circuit including the other diode section, a connection including an impedance from said diode to an intermediate tap on the source of potential, and a connection from the diode to the automatic gain control means in the carrier frequency amplifier.

26. The method of carrier wave reception which comprises the successive operations of amplifying the carrier, rectifying the amplified carrier, re-amplifying the rectified carrier, bal ancing a direct current component of the reamplified rectified carrier against a fixed direct current and permitting current to flow for con-y all trolling amplification when the relative levels and polarities of the balanced currents satisfy predetermined conditions.

27. The method of governing the gain of an amplifier which comprises rectifying the output of the amplifier, amplifying the rectified output, balancing the amplified rectified output against a steady current, and passing governing current to control the gain of the amplifier when the amplified rectified output reaches a predermined level relative to the steady current.

28. In combination with a diode rectifier circuit having a tuned input circuit, a load resistor in circuit with said tuned circuit between the diode anode and cathode, an electron discharge tube having at least a cathode, plate and control grid, connections from the control grid and cathode of the tube to points of different direct current potentials on said resistor, the grid connection point being negative with respect to the cathode connection, a network in shunt with said load resistor comprising a resistor` and an audio by-pass condenser in series, and said control grid connection including an adjustable tap in sliding contact with said series resistor whereby the impression on the grid of the audio component of the voltage developed across the load resistor may be varied without changing the said direct current potential difference between said grid and cathode.

29. In a radio receiver, the combination with a radio amplifier, a detector, a direct current amplifier working out of said detector, and having a plate-cathode resistance by-passed for radio frequencies, a diode having said resistance connected between the cathode thereof and the anode through a serially connected resistor and a direct current source, said source impressing a positive potential upon said anode, and a circuit connection for impressing the direct current potential of one of said diode elements upon said radio amplifier as a gain control bias.

30. A radio receiver as set forth in the above claim 29 wherein said destroyer, direct current amplifier and diode comprise elements within a single vacuum tube.

3l. In the operation of a radio receiver including a radio amplifier working into a rectifying system which produces a direct current voltage that varies inversely with the radio input to the receiver, a device of uni-lateral conductivity having an output resistance included in a gain control circuit of said amplifier, and a source of direct current potential, the method o maintaining normal gain of said amplifier for all radio input below a critical value and then varying the gain with changes in receiver input above that critical value which comprises impressing the output voltage of said rectifying system on said device in a sense opposing conduction therethrough, and impressing upon said device from said source a direct current voltage tending to produce conduction and of a magnitude neutralizing the blocking eect of said first impressed voltage when the latter falls to the value corresponding to the said critical radio input to the receiver.

32. A radio receiver comprising an amplifier with amplification control means, an electron tube having a cathode, anode, control grid and at least two auxiliary anodes arranged to receive electrons from the cathode without influencing or being influenced by other electrodes, a rectifier circuit embodying the cathode and an auX- iliary anode for rectifying signals and a uni-laterally conducting circuit embodying the cathode, a potential source and an auxiliary anode for automatically controlling amplification for signals above a determined level.

33. In combination, a detector-governor comprising a cathode, an amplifier section and two auxiliary anodes, a rectifier circuit comprising the cathode and one auxiliary anode, a governor circuit comprising the cathode and second auxiliary anode and an amplifier circuit comprising the cathode and amplifier section.

34. In a modulated carrier-current signaling system employing a carrier-current amplifier and rectifier, which rectifier produces a modulated uni-directional voltage, a direct current voltage connection from said rectifier to an element of said amplifier whereby the amplification is automatically regulated, said connection including a space discharge device of unidirectional conductivity, and a connection from said rectifier to a modulation current amplifier whereby the signal is further amplified, and an additional connection from the output of the modulation current amplifier to the output electrode of said rectifier for varying the potential of said rectifier output electrode in dependence on the intensity of received carrier current.

LOY E. BARTGN.

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