US2061710A - Automatic volume control - Google Patents

Description

Nov. 24, 1936. D MCCAA ET AL 2,061,710

AUTOMATIC VOLUME CONTROL Filed NOV. 9, 1929 4 Sheeis-Sheet l Nov. 24, 1936.

D. G. MccAA ET AL 2,061,710

AUTOMATIC VOLUME CONTROL I Filed Nov. 9, 1929 4 Sheets-Sheet 2 Nov. 24, 1936.

GRH) BIAS -o- D. G. MCCAA ET AL AUTOMAT I C VOLUME CONTROL Filed NOV. 9, 1929 cARmER VOLTAGE. E.

l l i l l i VOLTAGE AmPLaFxcATloN' PER STAGE NTERNM. PLATE inPEnANcE GRID BIAS 4 Sheets-Sheet 3 Nov. 24, 1936. D. G MCCAA ET AL AUTQMATIC VOLUME CONTROL F'iled Nov. 9, 1929 4 Sheets-Sheet 4 L CARRIER RHPLITUDE VOLTS IBOV Patented Nov. 24, 1936 AUTOMATIC VLUME CONTROL Application November 9, 1929, Serial No. 405,964

15 Claims.

This invention relates to radio receiving systems and has particular reference to the automatic control of volume oi the output of such systems. Y

One of the objects oi the invention is to limit the output volume to any predetermined level regardless ci the amplitude of the carrier wave input to the system.

Another object is to so control the output Volume of a radio receiving system that strong carrier waves are reduced to a predetermined level, while carrier waves which are weaker than that level will be totally unaffected. In other Words, unless a carrier Wave is present and is higher than the level setting, the radio receiving system will maintain its full normal sensitivity.

A further object of the invention is to provide `a more sensitive control than has heretofore been possible with systems of the prior art and which is obtained by deriving a small differential unidirectional voltage corresponding to the carrier voltage, amplifying this diilerential voltage, and then using the amplified voltage to bias the grid or grids of one or more tubes preceding thedetector tube oi the system.

A still further object of the invention is to provide a sensitive voltage control which, when incorporated with a receiving system, will function without producing hovvls due to the setting up of local oscillations or the leakage of undesirable oscillations from the input into the direct current amplifier.

Other objects will appear hereinafter.

The differential voltage is obtained by deriving a uni-directional voltage from the carrier in the output of a rectifying detector and opposing said voltage by an external source of unidirectional electro-motive force, the differential voltage being the algebraic sum of the derived voltage and the opposing voltage. 'Ihe differential voltage is then impressed on the grid of a direct current amplier where it is amplified and from the output ci this tube, it is impressed on the grid or grids of the vacuum tubes of the receiving system preceding the detector tube. Said grids are biased in accordance with the amplitude of the incoming carrier Wave, that is, if a strong carrier Wave comes in from the antenna and passes through the system, a large change plate current will take place in the output circuit of the detector tube, thereby producing a large differential voltage on the input of the direct current amplifier which, vin turn, puts a large bias on the grids of the tubes preceding the detector, thereby considerably cutting down the (Cl. 25d-20) amplification oi said tubes. On the other hand, if a weak carrier wave is impressed on the antenna, a small differential voltage is derived and a less negative bias is impressed on the grids of the tubes preceding the detector, thereby permitting the tubes to .amplify to a greater extent. v If the carrier wave is below the level setting, then there is no effect on the system and no control of volume occurs.

Some of the features of the volume control of the present invention which distinguish it from the prior art are:

1) The provision of a special radio frequency iilter in the grid circuit of the tube or tubes which are automatically biased and other filters in the circuit winch make for the diflerence between satisfactory operation of the system and a system which would set up undue howls caused by oscillations being generated in the system or due to the feed-back effect of the system.

(2) The use of a high impedance primary coil L' in the output circuit of the automatically biased tube or tubes.

(3) The use of a potentiometer voltage to buck the voltage derived in a time circuit in the plate circuit of the detector tube.,

(4) The use of a direct current amplier to increase the effect of the differential voltage.

(5) The use of a potentiometer carrying direct current only, instead of a signal voltage-divider in the iinal output circuit to effect control of output volume level. y

(6) The provision of an automatic biasing means on the grid ci the detector tube itself.

(7) The provision of an automatic bias on all of the tubes of the system up to and including the detector.

A clearer understanding of. the system and operation of the system will be had from the drawings, in which Fig. 1 is a Wiring diagram of a radio receiving system with the mcdiiications and additional apparatus required to carry out our invention with the use of a grid leak detector;

Fig. 2 shows a system similar to that of Fig. l except that in place oi the grid leak detector a biased detector is used;

Fig. 3 is a graphical diagram showing the various relations between the carrier wave voltage and the uni-directional grid biasing voltages of f the direct current ampliiier and the radio frequency amplifiers;

Fig. 4 is a diagram similar to Fig. 3, showing the relation between the biased voltage as compared With the voltage amplication in thaty stage, using a standard radio frequency transformer and using a radio frequency transformer with a high impedance primary;

Fig. 5 is a diagram explaining the relations shown in Fig. fl;

Fig. 6 shows the relation between the carrier amplitude in volts and the output to the speaker in volts for systems of the prior art and for the system of our invention at various level settings; and

Fig. '7 shows a modification in Which a low voltage filament-type tube, such as a UX 199, is used as the ampliiicaticn variationy element corresponding to V1 of Figs. l and 2 and using a curn rent amplifying tube, such as the UX 245 type, corresponding to V4 of Figs. 1 and 2.

Referring to Fig. l, the vacuum tubes V1 and V2 are radio frequency amplifiers, V3 a grid leak detector tube and V4 a uni-directional voltage amplifier tube of the screen grid type. The tubes are shown of the heater type but it is obvious that the iilament type tubes may be used Without departing from the invention. In order to prevent self-oscillation in this system, which may be due to the modications used in this invention, it is necessary to provide the grid circuit of each automatically biased tube with a lter system comprising condensers C1, Cz, C3 and the radio frequency chokes RFC, as in the grid circuit of. tube V1. The primary coil in the output circuit of tube V1 comprises, for example, sixty turns instead of the usual fifteen turns provides a high impedance in the output circuit to match the impedance of the tube V1, as hereinafter explained. A radio frequency by-pass condenser Ci is connected in series with the primary and is connected to the cathode return through condenser Cz and the ground. In the plate circuit of the detector tube V3 is a radio frequency choke RFC and a radio frequency by-pass condenser C3, While in series with the primary of the audio frequency transformer, is an audio frequency bypass condenser Cv. The direct current component of the plate current of the detector V3 is impressed on the time circuit RC which has its positive end connected to the slider of the potentiometer P, which, in turn is connected across a plate supply voltage of 22 volts. The negative end of the time circuit is connected to the grid of the tube V4. The screen grid `of the tube V4 is connected to a potential of 67 volts. The pla of the tube V4 is connected through resistance R1 which may be of the order of 200,000 ohms, to a plate supply voltage of approximately 90 volts. The end of the resistance R1 adjacent the plate of tube V4 is connected to the grid oi tube V1 through the special filter. By reason of the pote-ntial applied to the cathode, the grid of the tube V1 is arranged to have a negative bia-s of 3 volts with respect to the cathode when no bias is produced by the vacuum tube V4. The vacuum tub-e V2 may have the usual connections or may be so arranged as to also be biased from the output of the tube V4. The cathodes of all of the tubes are heated by the filaments which are supplied with alternating current from the transformer T. It will be noted that the cathode of the detector is connected, as is customary, to a point which is at a potential of 6 volts positive with respect to the ground. The tubes V1 and V2 are neutralized by condensers C5 to prevent selfoscillation due to the inherent capacities` of the tubes, in a well-known manner. The adjustment of the neutralizing point of condensers C5, however, is accomplished in a manner different from that of the prior art and is as follows: The slider of the potentiometer P is adjusted to its maximum positive position so that no plate current flows in the tube or tubes o be neutralized and then the adjustment of condenser C5 is made of minimum signal. rihis action occurs because a maximum positive setting on potentiometer P gives a maximum negative bias on tube V1 and, therefore, the tube is completely blocked except for the tube capacity and no plate current can flow. It is advisable to neutralize all the auton matically biased tubes in order that the cut-ofi` may be more nearly c nipletc. The neutralizing tap of the secondary of the transformer, which has the high impedance primary, should include as many turns to ground as the rimary does in order to neutralize over the entire frequency range.

The operation of the system is as follows2--A signal carrier Wave of certain average amplitude is impressed on the antenna and is ainpliiied by 1e tubes V1 and V2 and detected by the tube V3. It is characteristic of the grid leak type of detector that with no signal, a cert-ain direct current flows in the plate circuit and with signal, the current in the plate circuit is reduced, the reduction depending on the voltage amplitude of the incoming carrier. This direct current is made to ow through the resistance R which is shunted by the capacity C and comprises what is known a time circuit, the lower end of the resistance R being connected to the slider of the potentiometer P. The potential between the cathode lead and the negative end of the potentiometer is [i5 volts. The potential across the potentiometer resistance is 22 volts. Considering that a 2 milliampere i rent is ilo-Wing in the plate circuit of the detector with no carrier present, We may assume that l1, milliamperes Will flow with the carrier unde consideration present. if We assume a value of 0,000 ohms for resista .ce R, it is obvious that the voltage drop across R will be 20 volts with no signal present and l5 volts when the carrier is present. Also, the potential across R will be negative on the plate of the detector tube. Upon a study of the circuit between the negative end of R and the negative end of the potentiometer P, it will be seen that when no carrier is present, the voltage will be 20 volts negative on the grid of tube V4 with the slider at the negative end and 2 volts positive with the slider on the positive ond of the potentiometer. When a signal is present to the extent above mentioned, these voltages will be modified to l5 volts negative and 'l volts positive. respectively. The negative end of the potentiometer is connected to the cathode of the tube V4 which, if cf the UY 224 type, has such a characteristic that no current flows in the pl circuit until the grid is less than 2 Volts negative with respect to the cathode when using the plate and screen potentials indicated. Resistance R1 is connected so that the plate current of the tube Vi ows therethrough. As shown in the diagram, the potential drop across R1 will be negative on the plate but, of course, if there no current fiowing, there will he no potential drop. Con-- sidering the diiferential voltage available between the grid the cathode of the tube V4, it be seen that either with or With-out signal present, the potentiometer P may be so adjusted that the plate current will or Will not flovv through R1 as desired. As will be readily seen, by proper arrangement of voltage and resistance values applied to tube V4. the voltage variation across R1 will be an amplified reproduction of the voltage across R. Considering th-at an adjustment is made in which current flows through R1, the potential across it will be added to that of the source marked 3 volts, which is connected between the cathode and the grid of the tube V1 with the negative potential on the grid. As has been hereinbefore stated, an increase in the negative potential on the grid of tube V1 will reduce the amplification in that stage and because the amplification has been reduced, the carrier will reach the detector with a lesser amplitude than has been considered. The current through the resistance R will, therefore, be changed less than 1/ milliampere from its normal iiow and the voltage across the input terminals of the tube V4 will be more negative on the grid and the change in grid. voltage on tube V1 will be less than it was previously assumed. Like all electrical systems, this system will automatically adjust itself to give the desired output in accordance with the level setting of the potentiometer P.

The system including condensers C1, C2, C3 and chokes RFC prevents radio frequency currents from entering the Aresist-ance R1 and the plate circuit of the tube V4, while the condensers C1, Cs and C7 prevent audio o'r radio frequency currents from entering the input circuit of the tube V4. These precautions assure that no alternating current will be amplified by the tube V4.

It is important to note that during one-half cycle of the incoming carrier wave, the grid of tube V3 goes positive and grid rectification current iiows through the leak resistor R3. The voltage set up across this resistor has both .a unidirectional and an audio component. The latter component is applied to the grid of tube Vs which serves to amplify it. Thus audio frequency currents representing the demodulated signal appear across R3 due to grid rectification and these currents are applied to tube V3 which amplifies them. It will be apparent then that a stage of the system including a single vacuum tube, namely the detector tube, is provided with means for demodulating a modulated carrier, for deriving biasing potentials, and for lamplifying the demodulated signal.

In Fig. 2 is shown a modication of Fig. 1 in which a detector of the grid bias type is substituted for the grid leak detector. The time circuit RC is connected in the plate cathode circuit but instead of being connected between the plate and the potentiometer, as in Fig. 1, it is connected between the cathode and the potentiometer with one end of the potentiometer connected to a potential of 6 volts positive in the power supply. Because of the direction of the flow of plate current through it, the potentials across resistance R will be positive toward the detector cathode and negative towards the potentiorneter and power supply. The positive end of the resistance R is connected to the grid of tube V4 and the negative end is connected to the grid of the detector so that the detector is automatically biased by the time circuit RC in accordance with the amplitude of the carrier wave. The advantages of automatically biasing the Idetector are that it is prevented from being overloaded by being automatically biased to the best point forthe carrier amplitude. The vacuum tube V1 is arranged to be biased from the output tube V4 in the same manner as in Fig. 1. The vacuum tube V2 is so arranged as. to also be biased from the output of the tube V4. In this instance, however, the grid return of V2 is connected to an intermediate point on the resistance R1 so that the grid of V2 is biased to a lesser extent than the grid of tube V1. With this arrangement, matched tubes are unnecessary. It will be seen that the bias on V1 is more than that necessary to produce zero plate current when cut-oli in tube V2 begins. It is not advisable to bias the tube before the detector unless all other tubes are arranged to cut off on a lower amplitude signal. Otherwise, distortion will occur.

Although the plate to cathode voltage of V1 is indicated as 90 volts on the diagram, better cut-off will be obtained with 45 volts on the plate and one volt normal grid bias instead of 3 volts.

It will be noted from the connections in this figure that the action of the time circuit RC is to cause the grid of tube V4 to become more positive, or, in other words, less negative with an increase in carrier voltage, thereby causing f a greater plate current to flow through resistance R1, the greater plate current producing a greater voltage drop to make the bias on tube V1 more negative, thereby reducing the amplication of the tube and bringing the output of tube V3 back to normal. In other words, the action in this ligure differs from that in Fig. 1 in that an increase in the carrier produces an increase in the direct current iiow of the detector tube, while in Fig. 1, an increase in the carrier produces a corresponding decrease in the plate current of the detector tube, but in each case, the increase or decrease is made to affect the grid of tube V4 in the same manner, that is, in the first case, an increased carrier makes the grid more negative and in the second case, makes it less positive, the final result being the same.

In systems of the prior art, so little voltage is developed across the RC circuit that without amplication, almost no Volume control will occur. However, in the special case where one audio frequency amplifier only is used between the detector and the sound reproducer, there may be suflicient voltage available across RC to properly control the grids of V1 and V2.

In Fig. 3 is shown graphically the relation of the grid bias voltages on the direct current ampliier tube an-d on the radio frequency amplier plotted against the carrier amplitude.

t will be noted in this figure, in which curve a represents the bias on the grid oi tube V4 and curve b represents the bias on tube V1 of Fig. 1, that with the control of the carrier level set at a certain point, there is no biasing effect on the tube V1 until the carrier voltage reaches a certain point c and then an increase in the carrier voltage produces a corresponding increase in the grid bias on the tube V1 until the blocking limit is reached.

Figs. 4 and 5 explain graphically the purpose of using a high impedance primary in the plate circuit of tube V1. In Fig. 4, the curve e represents the voltage amplification per stage plotted against the grid bias of that stage when a standard transformer having a low impedance primary is used, while curve f represents the Voltage amplication per stage against grid bias when a special transformer having a high impedance primary is use-d. It will be noted that a bias of 11/2 Volts gives the maximum amplification in a standard transformer represented by the point h and an increase in bias to 3 volts produces a decrease in amplication, as designated by point i. On the other hand, in the curve f, the amplication is lower with a bias of 11/2 volts but reaches a maximum, as indicated by point g, when the normal bias is set at 3 volts. It is for this reason that a high impedance primary is used in the plate circuit of tube V1 and the normal grid bias on the tube is set at 3 volts, co 1responding to the point y in the curve e of Fig. 5. This curve shows the relation of the internal plate impedance against the grid bias of tube V1 and shows that a higher impedance occurs when a higher negative bias is used and, therefore, it is essential to use a higher external impedance to get maximum amplification. It is apparent that when this type of high impedance primary is used, a lower negative voltage is required en the grid to cut oil the signal.

In Fig. 6 are shown comparison curves for different settings of the level adjustment or the potentiometer P of the system of our invention as compared to automatic volume control systems of the prior art. rihe curve A represents the output to the speaker in volts against carrier amplitude in volts when no volume control or level adjustment is used. The output lreeps on increasing with increase the carrier until the overload point is reached, at which point, no substantial increase in output taires place. The curve B .shows the relation or the output to speaker to the carrier amplitude with a level adjustment set to the level of the dotted curve when one tube is automatically biased in accordance with systems of the prior art and curve C represents the output when two tubes are automatically biased in a simiiar manner. lio these two curves, the output continues to rise until the level F is reached, at which point, a decrease in the output is produced. With two tubes automatically biased, the curve C is produced in which a still greater decrease in output to the speaker is effected. In both these cases, however, the output is not nearly as close to the limit of the level as when the automa ic volume control of our system is used, as represented by the curve D, in which only one tube is biased, the grid bias being rst amplied by the direct current ampliier before being applied to the tube. rihe reason that the curve D is nearer the level adjustment than curves B and C is that the same increase in carrier as in curves E and C above the level setting would cause much more bias and, therefore, much more attenuation when an ampliiier is used, but because of the increased attenuation, less increase in carrier Voltage in the detector is necessary to bring the output down to the level of the system. The dotted curve J represents a level setting of 50% of the setting I and curve E represents the output when reduced 50% by an output voltage-divider, as is generally done in systems of the prior art. The curve K represents the output when the level adjustment is decreased 59% by means of the potentiometer P of our system. it will be noted that with a voltage-divider, peint F is brought down to the point l-l, which shows that the output is reduced in like amount for both weak and strong carriers. ln other words, a weak Signal is cut down to the same extent as a strong signal, whereas when a potentiometer is used, weak sig nals are unaffected, since the curve continues to rise to the point G without reduction in amplication and only at the pont G, which is 50% of the previous level setting, a reduction of the volume is effected and maintained at the level, as represented by curve l. From the iigure, it will be seen that a greater advantage is obtained by our improved system in that a carrier which is below the level setting remains unaffected and a stronger signal is produced than with the systems of the prior art and only carriers which are higher or stronger than the level setting are kept at a predetermined level and are kept to this level more closely than with other systems. Also a greater range of carrier amplitudes will be held constant, which is a feature of particular advantage in case of fading. This advantage may be readily perceived from Fie. 6 by comparing curve OEE with curve CGK particularly portions OH and OG, respectively. The area OGH which is cross-hatched represents the advantage obtained since the system according to our invention represented by portion CG gives a greater output to the speaker for the same carrier amplitudes between O--M than that obtained by the systems of the prior art represented by the portion OH.

Fig. '7 is a modification showing a filament tube er the 'UX 199 type substituted for the radio frequency amplier tube V1 and a current amplifier such as a UX 245 type, substituted for the voltage ampliiier tube Vl. In a system arranged in this manner, the reduction of amplication is obtained by a change in current flow in the I'llament or tube V1 instead of a change in negative bias on the grid thereof. rEhe filament oi the tube is operated at rated current and the filament current is opposed by the plate current from the tube When the plate current from tube V4 increases, it opposes the ilament current of tube V1 to a greater extent, reducing th-e filament temperature of the tube and thereby reducing the amplification.

In Figs. i and 2, the resistance R1 and condenser C1 function as a time circuit in like manner the time circuit RC, but their combined effects are diierent, because they are isolated by the tube V4, than they would be if they were directly connected in series or in parallel. Due to the arrangement of V4 with the time circuit RC in the gid circuit and the time circuit R1, C1 in the plate circuit, a much greater time lag occurs in the biasinor of tube V1 than would occur if the two time circuits were not isolated by the tube V4. The reason for this is that R1 does not shunt R and that the voltage is not applied to R1, C1 until the voltage across RC has built up to a substantial extent. r'his means that a more economical time system is produced in that the elements C and C1, R and R1 need not be large nd expensive. The limitation to the Value of R is that if it be too large, an excessive amount of detector plate voltage is lost.

The amplified differential voltage, as derived in the above systems, may be applied to the grid, as shown, or to the screen, the plate or the filament of any tube preceding the detector.

While we have shown several modications of our invention for the purpose of description and illustration of its principles. of operation, it is apparent that other changes and modifications may be made therein without departing from the scope of the invention. We desire, therefore, that only such limitations shall be imposed thereon as are indicated in the appended claims.

Vile claim:

i.. In a radio receiving system comprising a plurality of vacuum tubes including a detector, means for automatically controlling the output volume of said system comprising a resistor in the plate-cathode circuit of said detector for causing a voltage drop therethrough, means for amplifying said voltage, means for causing said amplified voltage to affect a vacuum tube preceding said detector, and a lter interposed in the input circuit of said vacuum tube to prevent feed-back of undesirable oscillations from the output of the detector.

2. In a radio receiving system comprising a plurality of vacuum tubes including a detector, means for automatically controlling the output volume of said system comprising a resistor in the output circuit of said detector for causing a Voltage drop therethrough to affect one of said vacuum tubes preceding said detector, whereby the eiiiciency of the system is modied, a lter interposed in the grid-cathode circuit of said vacuum tube to prevent feed-back of undesirable oscillations from the output of the detectors, said filter comprising a pair of condensers having their junction point connected to ground and to the tuning condenser in said grid-cathode circuit, la pair of choke coils, one of said choke coils having one terminal connected to the o-ther terminal of one of said condensers and to the grid return of said Vacuum tube, and the other choke coil having one terminal connected to the other terminal of the second condenser and to the cathode of said vacuum tube, and a third condenser connected across the remaining terminals of said choke coils.

8. In a radio receiving system comprising a plurality of vacuum tubes connected in cascade including a detector, means for automatically biasing one of the tubes preceding said detector to maintain the output of said system constant within predetermined limits, said means comprising a resistor for causing a potential drop therethrough to affect the bias on said tube preceding the detector, means for maintaining a high minimum negative bias on said tube, and a transformer associated with the output circuit of said biased tube having a primary coil of relatively high effective impedance to effect a quick cutoff of said tube at a relatively low biasing potential.

4. In a radio receiving system comprising a plurality of vacuum tubes including a detector, transformers connecting said tubes in cascade, means for automatically biasing one or more of the tubes preceding said detector to maintain the output of said system constant within predetermined limits, said means comprising a resistor in the circuit of said detector for causing a potential drop therethrough to aiect the bias on one or more of said tubes preceding the detector, and means for maintaining a high minimum negative bias on said tube, the transformers associated With said biased tube or tubes having primary coils of relatively high effective impedance to eiiect a quick cut-ofi" on the efficiency of said tubes at relatively low biasing potentials.

5. In a carrier Wave receiving system comprising a plurality of Vacuum tubes including a signal demodulator, energized from a single source of energy, the method of automatically controlling the output volume of said system Within predetermined limits in accordance with the amplitude of the input carrier Wave which comprises deriving a uni-directional voltage from the output of the signal demodulator, applying said voltage to the grid of the signal demodulator to affect the bias thereon, simultaneously causing said voltage to affect the bias on the grid of one of the tubes preceding the signal demodulator.

6. In a carrier Wave receiving system comprising a plurality of vacuum tubes including a detector connected in cascade, the method of automatically controlling the output volume of said system Within predetermined limits in accordance with the amplitude of the input carrier Wave Which comprises deriving a uni-directional voltage from the detector tube, causing said Voltage to bias the grid of said detector tube, and simultaneously causing said voltage to affect the bias on at least two of the vacuum tubes preceding the detector, one to a greater extent than another, in accordance with the v-ariations of said derived voltage.

'7. In a carrier Wave system comprising a plurality of vacuum tubes including a detector, one or more of the tubes preceding the detector being cf the low Voltage, low current filament type, the method of automatically controlling the output volume of said system Which comprises operating one or more of said tubes preceding said detector at the rated value of lament current, deriving a uni-directional current from the system, and causing said current to oppose to a greater or lesser extent the filament current of the tube or tubes preceding the detector, Whereby the efliciency of said tubes is modified.

8. In a carrier Wave system comprising a plurality of vacuum tubes including a detector, one or more of the tubes preceding the detector being of the low'voltage, low current filament type, the method of automatically controlling the output volume or" said system which comprises operating one or more of said tubes preceding the detector at the normal rated value of filament current, deriving a uni-directional current from the plate circuit of the detector, and causing said plate current to affect to a greater or lesser extent the filament current of the tube or tubes preceding the detector, whereby the efficiency of said tubes is modified in accordance with the amplitude of the input carrier Wave.

9. In a radio receiving system comprising a plurality of vacuum tubes of the heater type including a detector, means for automatically maintaining the output volume of said system constant in spite of variations in the carrier Wave, comprising a time circuit connected in the plate-cathode circuit of said detector, a voltageoperated thermionic vacuum tube having an indirectly heated cathode, a grid, a plate and a screen electi'ode, the grid of said tube being connected to one terminal of the time circuit and the cathode connected to the other terminal of the time circuit thru a source of potential and a voltage-divider, the plate of said tube being connected thru a resistance to a positive source of potential, and a connection from the junction point of the plate and resistance to the grid of one o1 the vacuum tubes preceding the detector.

10. In a carrier Wave receiving system comprising a plurality of vacuum tubes including a detector connected in cascade, the method of automatically controlling the output volume of said system Within predetermined limits in accordance with the amplitude` of the input carrier wave which comprises deriving a uni-directional voltage from the detector tube, causing Said voltage to affect the bias on one of the vacuum tubes preceding the detector to a greater extent than it does the bias on a succeeding one of said tubes preceding the detector so that the one tube will be blocked before the other.

l1. In a radio receiving system, means for amplifying the incoming signals at a frequency above audibility, including a vacuum tube having a control grid, an independent cathode, and an anode, means comprising another vacuum tube for deriving biasing potentials from signals received by the system, means for amplifying said derived potentials, comprising a Vacuum tube having a control grid, an independent cathode, and an anode, means for supplying the amplied potentials to the control grid of said rst-mentioned tube to automatically control the output level of the system in accordance with the received signals, and a single source of unidirectional potential supply furnishing the necessary normal uni-directional potentials to all of said vacuum tubes, the anode of said last-mentioned tube being energized by the same potential as energizes the control grid of said rstmentioned tube, and the cathode of said rstmentioned tube being energized more positively than the cathode of said last-mentioned tube by an amount suriioient to provide anode energi- Zation for said last-mentioned tube.

l2. A signaling system comprising an amplifier having a cathode, anode and control electrode, connected to a three electrode detector coupled to the output of said amplifier, which detector produces a uni-directional change or" voltage dependent on the alternating signal voltage irnpressed thereon, a volume control tube having a cathode, anode, and control electrode, a connection for coupling the said change of voltage to the control electrode of said Volume control tube, means for maintaining the cathode 0f said Volurne control tube at a potential greatly negative relative to said amplier cathode, means for maintaining the anode o said volume control tube at a potential normally slightly negative relative to said amplifier cathode, a resistance in series with the anode of said volume control tube for causing thereon a corresponding change of voltage whereby an increase in the current supplied to said rectier will produce an increase in the anode-cathode current through said volurne control tube, and a connection from the anode of said volume control tube to the control electrode of said amplier, whereby the amplification of said ainplier is regulated automatically.

13. In a signaling System, a vacuum tube ampliiier having a cathode and a control electrode, a Vacuum tube detector coupled to the output of said amplier, a volume control tube coupled to the output or said detector, said volume control tube having a cathode and an output electrode, means for maintaining the cathode of said volume control tube greatly negative relative to said amplifier cathode, means for maintaining the output electrode of said volume control tube normally slightly negative relative to said amplier cathode, means for causing said output electrode to become more negative in the presence Vof an amplified signal, and a direct current connection between said output electrode and said control electrode, whereby the amplification of said amplifier is regulated automatically.

14. A radio signal receiving apparatus which includes a carrier current ampliiier having a control electrode and a cathode, a detector tube having a grid, a cathode and an anode arranged for grid rectiiication, and connected to the output oi said amplifier, a resistor connected in the anode circuit or said detector tube, across which is developed a uni-directional rectiiied voltage which causes the voltage at said anode to become less positive upon an increase of anode current, a volume control tube having a cathode, an input and an output electrode, said input electrode being connected to said anode, whereby variations in the detector anode Voltage are impressed on said input electrode, means for causing the cathode of said volume control tube to be more positive than said input electrode, means for maintaining the cathode of said volume control tube greatly negative relative to the cathode of said amplifier, means for maintaining said output electrode normally slightly negative relative to the cathode of said amplier, a resistor connected between said output electrode and the cathode of said volume control tube, whereby said output electrode becomes more negative when the voltage at said input electrode becomes more positive and a connection from said output electrode to said control electrode, whereby an increase of the negative voltage of said output electrode decreases the amplification of said amplifier.

l5. A radio signal receiving apparatus which comprises a carrier current amplifier having a cathode and a control electrode, a detector tube of the grid-detection type having a plate electrode, a volume control tube having `a cathode, an input electrode and an output electrode, a resistor connected in the plate circuit of said detector tube, a connection from said input electrode to said plate electrode, means for maintaining the cathode of said volume control tube greatly negative relative to said amplier cathode, means for maintaining said output electrode slightly negative relative to said amplifier cathode, a resistor connected between said output electrode and the cathode of said volume control tube, and a connection between said output electrode and said control electrode, Whereby an increase in the incoming signal strength creates an increase in the negative bias on the control electrode of said amplifier.

DAVID G. MCCAA. REYNOLDS D. BROWN, JR.

CERTIFICATE GF CORRECTION.

Patent No. 21361571@ November 24, 1936.

'AVID Ga NCCAA, ET AL.

It is hereby Certified. that eiror appears in the printed Specification of Jehe above numbered patent requiring oorreoion es follows: Page 5, second Column, etike ou?J lines 56 'to 68 inclusive, Comprising claim lO, and for claims now appearing *ehe patent es numbers 11, 12, 13, 14 and 15 reed 10, 11; 12, 13 14- eepeetively; and that the seid. Letters Patent should 'be reed with these oozreetions therein that the Same may conform io the reood. o Cese in the Patent Office.

SigneL and. sealed this 24th dey August, A. D. 1957.

Leslie Frazer (Seel) Acting Commissioner of Patents.

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