US2085928A - Automatic volume control for radio receiving apparatus - Google Patents

Description

July 6, 1937. s. A. STEVENS ET AL ,0

AUTOMATIC VOLUME CONTROL FOR RADIO RECEIVING APPARATUS Filed Sept. 22, 1934 2 Sheets-Sheet 1 III-l- Q INVENTORS Sydney Arthur Stevens 72mm ATTORNEY and Lesgz'e Ernest Thongpsozz July 6, 1 93 7.

vs. A. STEVENS ET AL AUTOMATIC VOLUME CONTROL FOR RADIO RECEIVING APPARATUS Filed Sept. 22, 1934 2 Sheets-Sheet 2 SydneyAmlz INVEQITORS zuuS' evens and Les eEnne t7120122p'son. BY 51 1} THEIR ATTORNEY Patented July 6, 1937 UNlTED sr'ras PATENT orrics AUTOMATIC VOLUME CONTROL FOR RADIO RECEEVING APPARATUS tion of Pennsylvania Application September 22, 1934, Serial No. 745,146 In Great Britain September 30, 1933 Claims;

This invention relates to automatic volume control for radio receiving apparatus and has for its object to provide improved arrangements for eifecting control of this character.

Automatic control of the volume ofthe reproduced signal in radio-receiving apparatus is usually efiected by varying the grid potential relative to the cathode potential of one or more valves of the apparatus in accordance with the strength or amplitude of the received carrier wave so as to render this grid potential increasingly negative as the strength of the carrier wave increases and thus to reduce correspondingly the degree of amplification of the valve which is being controlled.

The variation of the grid potential of the controlled valve for this purpose is generally effected by the provision of a resistance arranged to be traversed by a direct current proportional to the strength of the carrier wave, the potential thereby developed across this resistance being applied to the grid of the controlled valve and it has been proposed to amplify this controlling potential by connecting a second additional resistance in the anode circuit of a valve upon the grid of which a potential derived from the first resistance is impressed, the amplified controlling potential being derived from this second resistance.

In radio-receiving apparatus embodying a detector of the dry surface contact type it is usual to connect a load resistance in the circuit of the detector and according to the principal feature of the present invention the potential across this resistance or any suitable portion thereof due to the rectified current traversing this resistance which is proportional to the strength of the carrier wave is arranged to be applied to the grid of a valve of the apparatus, the current in the anode circuit of this valve being thereby correspondingly modified and a potential derived from this modified anode current being impressed upon the grid of a Valve or valves so as to eifect an amplified volume control of this valve or valves.

Preferably the valve to the grid of which the potential derived from the load resistance is applied is the valve from which the detector is immediately supplied but this valve may be a valve preceding or following the detector supply valve or may be a valve specially provided for the purpose of amplifying the volume control potential derived from the load resistance.

Preferably a resistance is connected in the anode circuit of the valve above referred to and the potential across this resistance or a portion thereof is utilized for varying the grid bias potential of the valve or valves to be controlled.

The grid potential of the valves to be controlled by amplified automatic volume control is determined by the difference of the potential drops across two resistances. By making one of these resistances carry a substantially constant current such as the total anode current of all the valves in the receiving apparatus other than the valve utilized for amplification of the volume control current it is possible to render the potential drop across this resistance substantially constant. The potentials of the cathodes of all the valves except the amplification valve above referred to will thus be substantially constant and positive relative to the H. T. negative terminal. The anode current of the valve which is utilized as an amplification valve for effecting volume control is caused to traverse the other resistance before reaching the H. T. negative terminal and the potential of the positive-end of this resistance will then vary with respect to that of the remaining valve cathodes in a'manner which will be an amplified reproduction of the potential applied to the grid of this valve. The potential applied to the grid of the valve to be controlled is thus the difference between the potentials due to the potential drops in the two resistances.

The invention is illustrated by way of example in the accompanying drawings Figure 1 of which is a diagrammatic view showing the circuits of a portion of a radio-receiving apparatus embodying one form of the invention, Figures 2 and 3 being similar views of modified circuits embodying other forms of the invention. Figure 4 is a diagrammatic view of the complete circuits of a radio-receiving apparatus embodying a still further modification. 1

Referring now first to Figure 1 it will be seen that a portion of a superheterodyne receiving apparatus is illustrated comprising an I. F. valve V! which may be the last of a series of I. F. valves and a valve V2 which may be the preceding I. F. valve in the series or the preceding H. F. valve. The valve VI is shown as comprising an anode l, a grid 2 and a cathode 3 which is connected through resistances RI and R2 to the negativeiH. T. terminal as shown, this terminal being connected to the earth conductor iof the apparatus through a resistance R3. The tuned circuit of the anode I includes the primary winding 5 of a coupling transformer Tl, the secondary winding 6 of which is connectedto a detector face contact type and a load'resistance R4 one terminal 'I of the resistance R being connected through a wire 8 to a point 9 intermediate the resistances RI and R2.

The valve V2 similarly comprises an anode ID the tuned circuit of which includes the primary winding I I of a transformer T2, the grid I2 of the valve V2 being connected through the secondary winding 53 of a coupling transformer T3 and a wire I4 to a point I 5 intermediate the resistances RI and R2. The cathode I5 of the valve V2 is connected through a resistance R5 to the earth conductor 4. An adjustable point in the load resistance R4 is connected through wires II, I8 in series with the secondary winding I9 of the transformer T2 to the grid 2 of the valve VI.

It will be understood that the provision of the resistance R3 causes the potential of the earth suitable normal negative grid bias.

' When a signal is being received the mean potential of the grid I2 of the valve V2 will be the potential at the point I5 transmitted through the wire I l, and the mean potential of the grid 2 of the valve VI will be theresultant of the potential of the point 9 and the potential of the adjustable point in the resistance R4 to which the wire I7 is connected.

As the signal strength increases the current traversing the load resistance R4 will tend to increase but on the other hand the potential applied to the grid 2 from the resistance R4 by way of Wire Il will become more negative so that the anode current through the valve VI will tend to be reduced. This reduced current traversing the resistance R2 will decrease the drop of potential in this resistance so that an increase in the negative potential of the pointl will result and this potential transmitted to the grid I2 of the valve V2 will reduce the anode current of this valve and thus eiiect the desired amplified volume control. 7

It will be understood that the resistance R3 which is traversed by the anode currents of a number of the valves of the apparatus serves to maintain a normal grid bias for the valves relative to the cathodes connected to the earth conductor 4 and the potential at the point I5 is thus the resultant of the potentials due to the flow of currents in the resistances R2 and R3. 1

Referring now to Figure 2 a modified circuit arrangement similar to that of Figure 1 is illustrated in which delayed amplified automatic volume control is obtained by still further modifying the potential which is impressed upon the grid or grids of the valve or valves to be controlled.

For this purpose a resistance. R5 is connected in series with a dry surface contact rectifier M between the earth conductor 4 and the point I5 intermediate the resistances RI and'R2. The wire I4 leading to the grid or grids of the valve or valves to be controlled is in this case conance RI, but in this case the magnitude of theresistancerR2 is such that when the valve VI is receiving a weak signal, (so thatthe voltage drop across the resistance R4 is 'small theigrid bias on the 'grid 2 is low, and hence the anode current of the valve VI is relatively large) the voltage drop across the resistance R2 will be appreciably in excess of that across the resistance R3. Under these conditions the potential of the point I5 will be positive relative to the earth conductor 4. The fiow of current from the point l5 through the rectifier M in its reverse direction is however prevented by the rectifier so that since the resistance R5 is not being traversed by current the potential of point I9 will be that of the earth conductor 4, and hence the only grid bias applied to the preceding valves will be that resulting from the current in their own cathode resistances, such as the resistance R5 in Fig. 1. For weal; signals, therefore, the amplified automatic volume control is inoperative, and is delayed until a signal is received of such magnitude that the anode current of valve Vi is reduced to a value for which the potential drop across the resistance R2 becomes the same or less than the potential drop across the resistance R3. When this occurs, current will flow from the earth conductor 4 through the resistance R5, the rectifier M in its forward direction to the resistance R2. The

magnitude of the resistance R5 is so determined as to be much greater than the resistance in the forward direction of the rectifier M. The potential of the point I9 is therefore under these conditions very nearly equal to that of the point I5,

and any further increase in signal strength with 3 a corresponding reduction in the-anode current of the valve VI, will cause the volume control potential transmitted by the wire I4 to be substantially that of the point I5, so that the negative value of this potential will increase as the signal strength increases and will be an amplified reproduction of the grid control potential of the valve VI due to the action of the resistance R4. In the circuit of Figure 2, therefore simple automatic volume control is applied to the valve VI, and delayed amplified automatic volume control is applied to any desired preceding valves. It will be understood that instead of connecting the delay circuit it can if desired be arranged to operate prior to amplification in the circuit betweenthe load resistance R4 and the grid 2 of the valve VI.

Additional amplification of the volumecontrol potential can be effected by providing a resistance in the anode circuit of the controlled valve and deriving from thisresistance an amplified potential which is applied to the grid of a preceding valve or valves so that a cascade amplification action is obtained.-

Thevolume control termed quiet delayed automatic volume control can also be effected in receiving apparatus embodying the invention in the following manner.

The amplified automatic volume control is effected as above described by the variation in the drop of potential in the resistance connected in the cathode circuit of the control valve such as VI, while the quiet control is effected by the change in the potential across a resistance connected in the positive side of the anode circuit of'the. valve.' This potential which is positive relative to the potential of the earth conductor 4 varies in magnitude to a greater extent than the rectified signal voltage across the load resistance R4 on account of the amplifying action of the valve VI and may beused to control the grid bias potential applied to a L. F. valve, and by its considerable magnitudeis suificient to vary the grid bias of the L. F. valve from a value such thatthe valve passes no anode current at all, down to a point at which the valve operates normally.

In a preferred arrangement for this purpose illustrated in Figure 3 a suitable resistance R6 is interposed in the connection between the positive terminal of the H. T. source and the anode l of the detector supply valve VI utilized for amplification of the automatic volume control, the anode terminal 20 of the resistance R6 being connected through an adjustable resistance R? connected to earth at E to one terminal 2i of a gas discharge tube N the other terminal 22 of which is connected through a filter resistance R8 to the grid 23 of an L. F. valve V3 of the apparatus, the terminal 22 of the tube N being also connected to the earth conductor 4 through a grid resistance R9.

It will thus be seen that under quiet conditions the grid 23 which is connected to the earth conductor through the resistances R8 and R9 is at earth potential and by applying a positive potential to the cathode M a negative grid bias for the grid'23 is obtained.

The cathode 24 of the valve V3 instead of being connected directly to the earth conductor 3 is connected to a point of positive potential relative to earth which is greater than the negative grid bias potential necessary to cause the valve V3 to take a zero anode current. This potential may be obtained in any suitable manner, and as shown in Figure 3 the cathode 24 of the valve V3 is connected through a resistance RN] to a wire 25 which is connected to a point in the cathode resistance of the output valve or some other resistance in the apparatus in such a manner as to impress on the cathode 24 a suitable potential which is positive relative to the potential of the grid 23.

When a weak signal is being received of insufiicient strength to be worth reproduction, the voltage drop across the load resistance R l will be small and the valve VI will be operating at a low value of grid bias potential determined by the resistance RI, sothat its anode current will be relatively large and the potential of the terminal 20 will therefore be low relative to the earth conductor t on account of the large voltage drop across the resistance 6. Under these conditions the anode current of the valve V3 will be zero and the valve will not therefore be able to operate as an amplifier. Although therefore the H. F. and I. F. amplifying valves are working at their maximum sensitivity, there will be no audio output from the loudspeaker. When a stronger signal is tuned in, the voltage drop across the load resistance R4 will increase, and the potential of the grid 2 of the valve Vi will become more negative relative to that of its cathode 3. The valve V I will thus operate to effect simple automatic volume control in the manner above described and will cause amplified automatic volume control to be applied to the preceding valves.

As the anode current of the valve VI decreases the potential drop across the resistance R6 will also decrease and the potential of the terminal 29 will therefore become more positive relative to the earth conductor 4. The gas discharge tube N connected in the anode circuit between the terminal 2B and the resistance R9 has the effect of preventing the passage of current through this resistance until the potential of the terminal 20 increases to a predetermined value relative to the earth conductor 4 whereupon the tube N will become conducting and current will then pass through the tube and through the resistance R9 to the earth-conductor 4. The flow of current through the resistance R9 will cause a drop of voltage therein rendering the upper end of the resistance R9 positive relative to the earth conductor l, this potential being applied through the filter resistance R8 and its associated condenser as a grid bias to the grid 23 of the valve V3. The magnitude of the resistance R9 is so proportioned that the grid bias will be greater than the excessive negative bias already applied to the valve V3 as above explained. The grid bias or difference of potential between the grid 23 and the cathode 2 E of the valve V3 can under'these conditions be arranged to be of the normal value for the valve to operate as an amplifying valve. A further increase in the strength of the received signal will cause the anode current of the valve VI to be still further reduced and the potential of the terminal 28 will consequently be increased,

thus causing an increase in the current traversing the discharge tube N and the resistance R9. This increase of current would have the effect of still further reducing the bias of the valve V3 were it not for the fact that the resulting increase in the.

.the terminal it to a value sufficient to cause the discharge tube. N to become conducting, and hence the valve V3 will be operating on an excessive negative grid bias and will not pass the V unwanted signal. In order to adjust the predetermined signal strength at which the control shall become operative, the adjustable resistance R? is provided and this resistance may either be connected between the terminal 26 and earth, as shown in Figure 3, or between the terminal 20 and the H. T. positive terminal depending partly on the characteristics of the discharge tube employed, and also upon the H. T. voltages of 'the' receiving apparatus. It will be observed that the addition of this quiet control circuit in no way alters or-interferes with thesimple or amplified tautomatic volume control circuits or their operalOll.

The neon tube N may, if desired, be so mounted in the apparatus as to be visible and will thus serve as .a tuning indicator in the well known manner.

Furthermore, if the valve immediately preceding the detector is arranged to operate on the reflex principle, this valve will serve as an L. F. amplifier in addition to its other functions and the valve being provided with automatic volume control in-accordance with the invention low frequency automatic volume control will thus be obtained.

Referring now to the circuit arrangement for a superheterodyne receiving apparatus shown in igure 4 it will be seen that the aerial A is. coupled by means of a band-pass device B to circuit of a second I. F. valve VI. which serves asa supply valve for the detector D. The load resistance R4 is connected through an L. F. transformer Tl to the grid circuit of an output valve Vl the anode circuit of which is arranged to supply current tothe loud speaker (not shown) of the apparatus through a transformer TLS.

The rectifier D is connected in series with the load resistance R4 and a resistance RI I across the terminals of the secondary winding 6 of the transformer TI and the terminal 25 of the resistance RII is connected by a wire 21 to an adjustablepoint 28 in a potentiometer resistance RI2 one terminal of which is connected to the earth conductor 4 and the other terminal to a point of suitable relatively low potential.

Theterminal 29 of the resistance RII is connected by means of a wire 30 through a rectifier M2 in its reverse current direction to the point I5 intermediate the resistances RI and R2 the point I 5 beingconnected to a volume control wire I4 which is connected to the grid circuits of the valves V4 and V5 which are the volume-com trolled valves of the apparatus.

The anode I of the valve VI is connected through a condenser CI and a dry surface contact rectifier M3 to the point 9 intermediate the resistances RI and R2, the-rectifier M3 being associated with a load resistance S and a potentiometer resistance R13 connected between the point 9 and the H. T. positive terminal. The resistance RI3 enables a delay action to be obtained by applying an adjustable positive potential to the lower end of the resistance S so as to bias the detector M3 and prevent the detector rectifying received signals of below a predetermined strength.

When signals of sufficient strength are received, a negative potential is built up at the upper electrode of the rectifier M3,. this potential being transmitted through a filter device consisting of a resistance RM and its associated condenser to the grid 2 of the valve VI, thereby applying simple automatic volume control, and by the action of the resistances R2 and R3, as previously described, causing the valve VI to operate as an amplifying valve to apply amplified automatic volume control to the preceding valves. As regards obtaining the quiet control action a relatively large delay voltageis introducedinto the circuit of the second detector D, by connecting in the detector circuit a resistance RH across which a fall of potential is produced by tapping off a positive potential from the upper end of resistance R2, which for weak signals is arranged to have a potential appreciably higher than that of the earth conductor 4, so that current will flow from the point I5 through the rectifier M2, wire 39, resistance RI I, wire 2'5 to the earth conductor 4 through the potentiometer resistance RI 2. The effect of this current will be to make the point 29 positive relative to the point 26; some of ,the current in the circuit will therefore flow through the secondary winding 6, rectifier D and the resistance R4, as the Whole of this circuit is in parallel with the resistance RI I. If the magnitude of the current thus flowing is arranged to be sufiicient, the rectifier D will always be operating on its forward characteristic, and will not there fore rectify even though appreciably large signals may be generated in the windings of the at the aerial and should not be permitted to reach the loud speaker. When a stronger signal is received, the efifect of the circuit including the rectifier M3 will'be to apply a larger control to valve Vi, and the point at which this control becomes operative can be determined by the amount of delay introduced from the potentiometer resistance RI3. One effect of this control voltage is to apply simple automatic volume control to the valve VI, a second effect being to apply amplified automatic volume control to the preceding valves, and if desired this amplified volume control may be delayed by a delay circuit consisting of a rectifier M and a resistance R5 indicated in dotted lines in Figure 4 and operating in the manner already described. The third eirect of this control voltage, however, is to reduce the potential of the point I5 below that of the point 2%, so that instead of current flowing through the resistance R! I in the direction of the arrow, there is a tendency for the current to reverse. The rectifier M2 prevents this reversal, so that there is no longer any bias of either polarity applied to the circuit of the second detector D, which then operates in the normal manner. It will be evident that by suitably proportioning the values of the resistances the detector circuit can be made to function at any desired signal strength.

In order to prevent a received signal of temporarily very low value due to fading from failing to be transmitted, a condenser C of relatively large capacity is connected across the terminals of the resistance RI I as shown.

The receiving apparatus of Figure 4 is shown asrprovided with terminals P. U. for connection to the pick-up device of a gramophone and when the apparatus is being employed for the reproduction of gramophone records the I. F. valve VI is utilized as a first L. F. amplifying valve in the well-known manner, switches SI and S2 being under these conditions adjusted from the positions shown in full lines to the positions shown in dotted lines.

In all the circuits'above described embodying the invention it will be noted that simplautomaticvolume control is arranged to be supplied to a valve such as the last I. F. valve which is 7 subject to a relatively high voltage so that a high control potential cannot be impressed thereon without risk of distortion in operation. The amplified volume control, on the other hand .is arranged to be applied to an earlier valve or valves of the receiving apparatus which being subject to relatively lower voltages is capable of having relatively high control potential im-' pressed thereon without distortion.

The invention is evidently not limited to the particular circuit connections above described and illustrated by way of example which may be varied in many respects without exceeding the scope of the invention.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to beperformed, we declare that what we claim is:

1.In receiving apparatus embodying a plurality of electron amplifying valves and a detector the combination.'comprising, a first resistor connected in the load circuit of saiddetector, a firstcircuit means to connect at least a portion of said reistor' across the grid and cathode of the valve immediately preceding the detector to effect simple automatic volume control for that valve, a current sourcehavingits positive terminal connected to the anodes of said valves, a ground conductor connected to the cathode of each of the valves ahead of the valve supplying the detector, a second resistor interposed between the negative terminal of the source and the cathode of the valve supplying the detector, at third resistor interposed between the negative terminal of the source and said ground conductor to create a given potential for said conductor, and another circuit means connected with the grid of at least one valve ahead of the valve supplying the detector and including an asymmetric unit connected between the ground conductor and the terminal of said second resistor remote from the negative terminal of the source and said unit disposed with its forward direction toward said terminal of the second resistor to effect delayed amplified automatic volume control for said other valve.

2.,In receiving apparatus embodying a plurality of electron amplifying valves and a detector the combination comprising, a resistor connected in the load circuit of said detector, circuit means to connect at least a portion of the resistor across the grid and cathode of the valve immediately preceding the detector to effect simple automatic volume control for that valve, 2. current source for the anode circuits of 'said valves, a second resistor interposed in the anode circuit of said preceding valve between the negative terminal of the current source and the cathode, a third resistor interposed between the negative terminal of the source and the cathode of another one of said valves, and another circuit means including a fourth resistor and an asymmetric unit connected between the terminals of said second and third resistor remote from the source to effect delayed amplified automatic volume control for said other valve.

3. In receiving apparatus embodying a plurality of electron amplifying valves and a detector the combination comprising, means to establish a normal negative grid bias potential for the valve immediately preceding the detector, means including a first resistor interposed in the load circuit of said detector and having connection to the grid of said preceding valve to establish simple automatic volume control for that valve, a source of anode current for said valves, a second resistor interposed between the negative terminal of the source and the cathode of said preceding valve, a third resistor interposed between the negative terminal of the source and the cathode of another one of said valves, said second and third resistor characterized by the normal poten tial drop across the third resistor being less than that across the second resistor, a connection including a fourth resistor and an asymmetric unit between the terminals of said second and third resistor remote from the current source and with the forward direction of said unit toward the terminal of the second resistor, and means to connect the terminal between said unit and the fourth resistor with the grid of said other valve whereby delayed amplified automatic volume control for said other valve is effected.

4. In receiving apparatus embodying a first and a second electron amplifying valve and a detector the combination comprising, means interposed in the grid circuit each valve to effect a normal negative grid bias potential, a source of current for the anode circuits of the valves, a first resistor interposed between the negative terminal of the source and the cathode of the second valve, a second resistor interposed between the negative terminal of the source and the oathode of the first valve, said resistors characterized by the normal potential drop across said first resistor being greater than that across said second resistor, a circuit connection including a third resistor and an asymmetric unit connected between the terminals of said first and second resistors remote from the source and with the forward direction of the unit toward the terminal of the first resistor, means including a resistor in the load circuit of the detector for applying a potential between the terminal of the first resistor remote from the source and the grid of said valve, and other means to connect the terminal between said unit and the third resistor with the grid of the first valve.

5. In receiving apparatus including a high frequency amplifying valve, a detector and a low frequency amplifying valve the combination comprising; a first resistor interposed in the load circuit of the detector, means to connect at least a portion of said resistor with the grid of the high frequency tube to effect automatic volume control of that valve, a second resistor interposed in the anode circuit of said high frequency valve, means to establish a normal negative grid bias potential for the low frequency valve and characterized by effecting substantially normal zero anode current of that valve, circuit means including a resistor and a gas discharge tube connected between the terminal of said second resistor toward the anode of the associated valve and the grid of the low frequency valve, and means including a source of alternating signaling current connected with the grid of the high frequency valve to vary the potential of said grid with respect to the cathode in accordance with said signaling current whereby the potential applied to said circuit means is varied to modify the normal negative grid bias potential of the low frequency valve to effect amplification of the output of the detector.

6.In receiving apparatus embodying a high frequency valve, a detector and a low-frequency valve the combination comprising; a grid circuit for the low frequency valve connected between the grid and a ground conductor, said circuit including two resistors and a winding inductively coupled with the output of the detector, means connected between the cathode of the low frequency tube and such ground conductor to effect a quiet grid bias that gives substantially zero anode current, a resistor and a winding serially interposed in the anode circuit of the high frequency valve with said winding inductively coupled with the input of the detector, means including a source of alternating signaling current connected with the grid of the high frequency valve, and another circuit means including a discharge'tube connected between the terminal of the last mentioned resistor toward the anode of the high frequency valve and the mid terminal of the two resistors of the grid circuit of the low frequency valve whereby the potential effected by the current of the anode circuit of the high frequency valve on said discharge tube in response to said signaling current is operative to modify the grid bias of the low frequency valve.

7. In receiving apparatus embodying a high frequency valve, a detector and a low frequency valve the combination comprising; a grid circuit for the low frequency valve including a winding coupled with the output of the detector, means including a source of potential connected with said grid circuit and characterized by establishing a quiet grid bias potential that effects substantially zero anode current, and anode circuit for the high frequency valve including a winding coupled with'the'inp ut of the detector, means including a source of alternating signaling current connected with the grid of the high frequency valve, and a circuit means including a discharge tube connected between a point of varying potential of the anode circuit of the high frequency valve and the grid circuit of the low frequency valve to modify the quiet grid bias potential in response to the signaling current applied to the high frequency valve whereby amplification of such signal'energy after detection is effected. V

8. In receiving apparatus including a high frequency amplifying valve, a detector and a low frequency valve the combination comprising; a first circuit means including a source of alternating signaling current coupled with the grid circuit of the high frequency valve, a second circuit means including a first and a second resistor as well as the detector and a winding, said winding coupled with the anode circuit of the high frequency valve to inductively receive an electromotive force in response to the amplified signaling current, grid circuit means for said low frequency valve and including said first resistor,

and other circuit means including a rectifier and a current source connected across said second resistor, said rectifier disposed to pass current which flows in said second resistor in a direction opposite to that supplied through the detector in' response to the electromotive force induced in the winding of said second circuit means whereby the detector operates on its forward characteristic and quiet automatic volume control for the low frequency valve is effected. V

9. In receiving apparatus including a high fre-' quency amplifying valve, a detector and a low frequency valve the combination comprising; a

first circuit means including a source of alternating signaling current coupled with the grid circuit of the high frequency valve, a second'circuit meansincluding a first and a second resistor as well as the detector and a winding, said winding coupled with the anode circuit of the high frequency valve to inductively receive an electromotive force in response to the amplified signaling current, a third circuit means including a first rectifier and a load resistor connected between the anode and cathode of the high frequency valve, said rectifier disposed with its forward direction toward the cathode, means to connect said load resistor with the grid of the high frequency valve to effect automatic volume control for said valve in response to variations effected in the current supplied to the anode of said valve, grid circuit means for said low frequency valve and including said first resistor,

and a fourth circuit means including a second rectifier and a current source connected across said second resistor, said second rectifier disposed to pass current which flows in said second resistor in a direction opposite to that supplied through the detector in response to the electromotive force induced in the winding of said second circuit means whereby the detector operates on its forward characteristic and quiet automatic volume control for'the low frequency valve is effected. V

10. In receiving apparatus including a first stage and a second stage high frequency valve, a detector and a low frequency valve the combination comprising; a first circuit means including a source of alternating signaling current coupled with the grid circuit of the first stage high frequency valve, a second circuit means including a first and a second resistor as Well as the detector and a winding, said winding coupled with the anode circuit of the second stage high frequency valve to inductively receive an electromotive force in response to the amplified signaling current, a third circuit means including a first rectifier and a load resistor connected between the anode and cathode of said secondstage valve, said rectifier disposed with its forwarddirection toward the cathode, means to connect said load resistor with the grid of said second stage valve to effect automatic volume control for that valve in response to variations effected in the current supplied to the anode of said second stage valve, a source of current having its positive terminal connected with the anodes of said valves, a ground conductor connected with the cathode of said first stage valve, a third and a fourth resistor connected between the cathode of said second stage valve and the negative terminal of said current source, a fifth resistor interposed between the ground conductor and the negative terminal of the current source, means to connect the mid terminal of the third and fourth resistors with the grid of said first stage valve to effect amplified automatic volume control for that valve in response to variations effected in the current supplied to the anode of said second stage valve, grid circuit means for said low frequency valve and including said first resistor, and a fourth circuit means including a second rectifier and a current source connected across said second resistor, said second rectifier disposed to pass current which flows in said second resistor in a direction opposite to that supplied through the detector in response to the electromotive force induced in the winding of said second circuit means whereby quiet automatic volume control for the low frequency valve is effected.

SYDNEY ARTHUR STEVENS. LESLIE ERNEST THOMPSON.

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