US2046237A - Volume control for amplifiers - Google Patents

Description

June 30, 1936. 5 BALLANTmE 2,046,237

VOLUME CONTROL FOR AMPLIFIERS Filed July 5, 1929 4 Sheets-Sheet l 3d Grid Wm H afkoznetgo.

J1me 1936- s. BALLANTINE 2,046,237

VOLUME CONTROLFOR AMPLIFIERS Filed July 5, 1929 4 Sheets-Sheet 2 Rad/'0 Frequency 07,011) l/faqe gwowntot:

June 30,)936. I s BALLANTINE 2,046,237

VOLUME CONTROL FOR AMPLIFIERS Filed July 5, 1929 4 Sheets-Sheet 5 June; 30, 1936, s. BALLANTINE VOLUME CONTROL FOR AMPLIFIERS Filed July 5, 1929 4 Sheets- Sheet 4 f a g mama: AMA 3 v f g 7 z i I Patented June 30, 1936 UNITED STATES VOLUME CONTROL FOE AMBLIFIEBS Stuart Ballantine, ,Mountain Lakes, N. 1., assignor, by mesne assignments, to Radio Corporation of America, Duration of Delaware New York, N. Y., a cor-- Application July 5, 1929, Serial No. 376,163

41 Claims.

This invention relates to methods oi,-and apparatus for, controlling the transmission in amplifiers, and particularly to methods of, and apparatus for, extending the range of amplification control in multi-stage amplifiers throughout which distortionless amplification may be obtained.

It has been customary to control the amplification oi'an amplifier stage by varying theener gizing voltage impressed upon an electrode of the amplifier tube, for example the grid bias, and in the case of cascaded radio frequency, or carrier wave; amplifiers, a wide range of controlhas been secured by simultaneously varying the bias on the grids of all of the amplifier tubes. This conventional method of controlling radio frequency amplification is described in my copending application Ser. No. 231,273, filed Nov. 5, 1927 patented July 26, 1932 as U.,S. Patent No. 1,869,331, relating to a method of, and apparatus for, automatically controlling the amplification in accordance with received signal energy. It has been found experimentally, however, that if the several grids are biased equally, a value of common grid bias is reached at which the relation between the input and output voltages of the amplifier becomes non-linear.

Objects of the present invention are to provide methods of, and apparatus for, maintaining distortionless amplification while varying the amplification over a wide range. Further objects are to increase the range of amplification control throughout which cascaded stages operate as a linear amplifier. More specifically, objects of the invention are to provide a method of, and apparatus for, amplification control which will increase the upper limit which the input signal voltage may reach before the distortion becomes objectionable.

These and other objects of the invention will be apparent from the following description, when taken with the accompanying drawings in which:

Figs. 1 and 2 are diagrams comprising curves representing the relation between input voltage and output voltage.

Fig. 3 is a diagram illustrating the ranges through which the bias voltages of successive stages may be varied while maintaining distortionless amplification,

Figs. 4, 5, and 6 are fragmentary diagrams of cascaded amplifier circuits embodying the invention.

The novel features which I'believe to be characteristic of my invention are set'forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawings in which I have indicated diagrammatically several circuit organizations whereby my invention may be carried into effect.

The curves of Fig. 1 were plotted from data taken with a four-stage radio-frequency amplifier which had been designed to supply a maxi- 10 mum of 20 volts to a high-voltage linear detector. The amplitude was to have been maintained at 10 volts, the 20 volt limit being set to take care of 100% modulation, The various curves represent the relation between the radio 15:

frequency output and input voltages for various grid bias voltages, the particular bias voltage which was common to all stages being indicated on Fig. 1 adjacent the respective curves.

It will be seen that the amplifier system re- 20 mains linear until the bias voltage reaches about 9 volts, and that it departs rapidly from linearity as the common negative bias is extended beyond that point. Considerable distortion occurs when the control voltage is made highly 25 negative to reduce the amplification for strong input signals, and even if the output voltage were maintained at 10 volts by automatic or manual control of the common grid bias, the audio output of the detector would not be constant since 30 the cut-off efiect shown in Fig. 1 effectively increases the degree of modulation of the signals.

These effects become of importance when the input signal level is high (as, for example, when the radio receiver is located near a transmitting station), and their effect is to limit the range of control; that is, to limit the range of input voltage over which the signal may vary before distortion appears.

Thebasis for the method of control which I employ may be understood from a consideration of the curves of Fig. 2, which set of experimental curves shows the relation between radio frequency input and output voltage for a single stage 01- an amplifier. It is to be noted that the curves are plotted with logarithmic coordinates in order that a wide range of voltages may be represented. Each curve represents the relation between radio frequency input and output voltages for a fixed grid bias, the value 01' the bias for each curve being indicated adjacent that curve on Fig. 2.

It will be seen that up to a certain point, for any given bias voltage, the relation between radio frequency input and output voltage is approxi- 7 gion of distortionless operation. To avoid distortion in a cascaded amplifier, the grid bias and the radio frequency input voltage of each stage must be so related that they lie to the left of the bounding curve RE, that is, in the region of linear response. The straight line RT completes the boundary and represents the residual transmission through the amplifier stage, which is, of

course, linear, and which may arise in several ways.

In a shielded tetrode stage without provision for neutralizing the effect of a small residual unshielded plate-to-control-grid capacity, it would arise from the electrostatic coupling through this capacity. In the case of an ordinary unshielded triode with a balancing network, it may arise from a slight unbalance, intentional or accidental. It may also be intentionally provided by coupling in the circuits external to the tube. This leakage is often useful in adjusting the linear boundary, and it permits the use of higher radio frequency input voltages without distortion.

The set of curves of Fig. 2 reveals the important fact that the higher the radio frequency voltage output desired from the stage, the smaller becomes the range over which the amplification can be varied. Since the voltages in all stages are different, operation in accordance with the present invention comprises controlling the overall amplification over the broadest permissible range by a graduated variation'of the ampllfication in the individual stages, the ranges of control for the individual stages being so chosen as to keep all stages in the region of linear response. The burden of control is thus placed upon the stages in which the signal voltages are lowest, and in this way the range of control is extended far beyond that which is possible in the known arrangements in which the biases ofall stages are equal, or are varied at the same rate.

This considerable extension of the range of distortionless control is shown graphically in Fig. 3, which is a diagram showing the voltages to be applied to the various grids of an amplifier comprising cascaded stages of the characteristics shown in Fig. 2.

It is assumed that a high voltage detector is connected to the output terminals of the final radio frequency stage and that the maximum output to the detector is to be 20 volts. On the Fig. 3 diagram, the fixed point D indicates this value of 20 volts at which the amplifier output bias were varied at the same rate on alltubes,

the limits of the range of variation, without distortion, at the input terminals of the amplifier, will be represented by points A and G, since the small variation which is permitted in the final stage limits the ranges of control on the first and second grids to the regions A'G and BF, respectively.

By departing from the prior practice of emaosaasv ploying a common grid bias for all stages, the range of control is extended for the first and second stages. Distortion in the final stage is elimi-' nated by restricting the output voltage of the preceding stage to a maximum of 2.2 volts, point C 5 in Fig. 3. The data of Fig. 2 shows that the bias of stage 2 may be increased negatively until the input voltage for that stage attains a value of 1 volt, point B, Figs. 2 and 3. Similarly, in Fig. 2 the curves show that for an output of 1 volt, the 10 input voltage for the first stage may be 0.75 volt, point A. The range of control has thus been extended to the value AG, Fig. 3, and it will be seen that its magnitude is enormously greater than the range A'G which is permissible when common bias voltages are employed.

In the circuit diagram which illustrates the invention as embodied in a radio receiver of the type including an automatic volume control, Fig. 4, only those parts which are of interest in connection with the present invention are shown in heavy lines.

The receiver includes three tuned radiofrequency amplifier stages employing tetrodes, or screen grid tubes, T1, a triode detector, and two 25 audio amplifier stages. These tubes, and the rectifier tube T: which forms part of the auto- III ' matic volume control system, are of the alternating current type, and the circuits (not shown) for supplying current to the tube heaters may be of the usual type.

So far as radio frequency currents are con-' cerned, the low potential sides of all circuits are at ground potential, being terminated at the shielding, or ground, line I. Plate current is supplied from batteries, or preferably a power supply device, not shown, which is connected across terminals +B, B. An intermediate point of the voltage divider 2, which is shunted across the plate supply terminals, is connected to the ground line I by a lead 3.

The automatic volume control is applied only to the first two radio frequency stages, the inductance L: of. the third stage being connected directly to the ground line I, while the inductances La of the preceding stages are grounded through by-pass condensers C. The cathode circuits of the radio frequency stages include grid bias resistors 4 which determine the bias on the third stage and the normal operating point for the first two stages.

The operating potentials for the volume control tube T2 are obtained by connecting the oathode, through lead 5; to a point in voltage divider 2 at which the direct current potential is less than that of the grounding lead I; the anode of tube T: being connected through series resistances B,

I and lead Ste-the ground line I, and the grid being connectedthrough leak resistance 9 and so adjustable contact III to that portion of voltage divider which is at less than ground potential.

The grid of the volume control tube '1: is connected, through condenser I I and lead I 2, to the grid of the detector tube, and the output of the tube T2 is applied to the low potential'tenninals of the inductances L: of the first two stages by leads ll, II respectively.

In accordance with the present invention, the range of control impressed upon the stage is graduated by connecting lead I 3 to the anode of the control tube, and lead I I to the Junction of series resistances 8, 1.

As explained in my aforesaid patent, the output 15 the bias voltage of the second tube may be varied is less than the bias voltage range of the first tube.

The value of carrier voltage at which the automatic control starts to function is regulated by the variable bias voltage tap ill of tube T2. The input voltage regulator I5 is provided to keep strong signals from exceeding the upper limit of distortionless control, point A, Fig. 3.

The invention is equally applicable to multistage amplifiers in which the amplification control is effected by the variation of the other voltages of the tubes, either in conjunction with a simultaneous variation of the grid bias, or separately.

For example, Fig. 5 illustrates the application of the invention to a cascaded amplifier in which the control of amplification is effected by varying the potentials impressed upon the screen-grids of tetrodes. The general circuit arrangement of the amplifier forms no part of the invention, and, therefore, will not be described in detail.

The volume control circuit elements are shown by heavier lines, and comprise a battery IE, or other suitable source of current, and a series of voltage dividers for regulating the voltages impressed upon the screen-grids G2 of the cascaded tetrodes T1, T2, T3. The resistance elements H of the voltage dividers are of identical construction, and the switch arms I8 are mounted on a common shaft for simultaneous operation by a suitable volume control knob, or dial, l9. In accordance with the present invention, the several switch arms iii are insulated from each other by non-conducting sections 20 of the operating shaft, and the switch arms are angularly displaced from each other to place, for all adjustments of the control device, progressively higher voltages upon the screen-grids of the succeeding tetrodes of the cascaded amplifier. The angular displacement of the contact arms I8 is so chosen, with respect I trodes of cascaded tubes.

to the changing slope of the'gain-control voltage characteristic of the tetrodes, that the operating pointsof succeeding stages fall upon portions of the curve which are of different slope.

For a given angular adjustment of the control knob l9, the control voltages are all changed by equal increments, but the changes in amplification are not equal in the several stages, being progressively smaller in succeeding stages.

As shown in Fig. 6, the control device-for an amplifier circuit, of the general type illustrated in Fig. 5, may comprise a gang voltage divider having a series of identical resistances I1 and aligned contact arms l8 when progressively higher voltages from the current supply source iii are impressed across the resistances ll of succeeding stages. Although this arrangement produces progressively greater changes of control voltages in succeeding stages, the corresponding changes in amplification are progressively smaller since the several tetrodes are operating upon different portions of their characteristic curves.

The specific control circuits which I have described illustrates the general applicability of the basic invention to the various typesof amplification control which are based upon a regulation of the operating potentials impressed upon the elec- It will be apparent to those familiar with the design and construction of amplifiers that the graduated amplification control may be provided in cascaded amplifiers in which the overall amplification is regulated by varying the plate potentials, or the cathode, or cathode heater, potentials in a plurality of stages.

The invention contemplates the graduation of the ranges of control in a cascaded amplifier, and it will be apparent that there is wide latitude in the choice of the electrical circuits and the me-,-

chanical details of the apparatus which may be employed for varying, at difierent rates, the amplification of the individual stages of a cascaded amplifier. It is therefore to be understood that control circuits and control apparatus other than the specific embodiments described herein fall within the scope of my invention as set forth in the following claims.

I claim:

1. In a. transmission system including cascaded tube stages for amplifying an incoming signal at radio frequency, the method of maintaining a uniform and distortionless transmission level which comprises simultaneously varying the amplification of theseveral stages at different rates. 2. In the operation of a tube amplifier including a plurality of stages for successively amplifying an incoming wave without change of frequency, the method of extending the range throughout which distortionless volume control may be efiected which comprises progressively decreasing the range of control in successive stages of said amplifier.

3. In the operation of cascaded amplifier stages for amplifying an incoming wave at radio frequency and of the type having linear and nonlinear response ranges, the method of maintaining an overall linear amplification while controlling the output volume, which comprises graduating the volume control impressed upon the separate stages in accordance with the range of linear response of the respective stages.

4. In the process of .varying the amplification of cascaded radio frequency amplifier stages by impressing upon an element of each stage a; control voltage derived from and varying in magnitude with received signal energy, the method which comprises progressively decreasing the range of control voltages impressed upon succeeding stages.

5. In a transmission system including cascaded amplifier stages operating at the same frequency, the method of maintaining distortionless amplification while varying the overall amplifica tion which comprises-determining for a; predetermined maximum output the limits of the respective ranges of linear response of the individual stages, and adjusting the range of values of the variable volume control elements of the individual stages to maintain the operation of each stage within its respective range of linear response.

6. The combination with a plurality of cascaded tube amplifier stages operating at the same frequency, of volume control means automatically responsive to signal amplitude variations for effecting progressively smaller changes in the amplification of succeeding stages. v

'7. An electrical transmission system of thetype including a plurality of cascaded tube amplifier stages all amplifying received energy at the same frequency, and means automatically responsive to signal amplitude variations for varying an energizing voltage of each stage to control overall 7 5 amplification of .said system, characterised by the fact that said amplification means includes elements progressively decreasing the range throughout which the energizing voltages of succeeding stages may be varied.

'8. The combination with a plurality of cascaded amplifier stages for successively amplifying incoming energy at its received frequency. of means automatically responsive to signal amplitude variations for varying an amplification-controlling voltage applied to each of said stages, and

circuit elements in said voltage-variation means for progressively decreasing the voltage changes applied to successive stages.

9. The invention as set forth in claim 8, wherein said voltage-variation means comprises a tube rectifier, an input circuit for said rectifier and shunted across the output of said amplifier.

stages, and connections for applying the output of said rectifier to the grids of said stages; and said circuit elements comprise resistance in the rectifier output circuit.

10. The combination with a cascaded tube amplifier, and means for rectifiying carrier wave energy to produce a direct current output, of circuit connections for impressing upon a tube element in each of a. plurality of stages a potential determined in magnitude by the direct current output, and means for progressively decreasing the magnitude of the voltage so impressed upon succeeding stages.

.11. The invention as set forth in claim 10 wherein said rectifier means comprises a tube having a resistance in the plate circuit thereof, and the circuit connections are so made to spaced points in said resistance that a lesser fraction of the voltage, drop across said resistance is applied to succeeding stages of said amplifier.

12. In an electrical transmission system-of the carrier wave type, a plurality of cascaded-tube amplifier stages, a ground line and circuit connections for maintaining the low potential terminals of the input circuits of said stages at the carrier wave potential of said ground line, resistors in the cathode circuits of said stages for establishim a normal direct current bias of said stages, and means automatically responsive to signal amplitude variations for varying the bias voltages of said stages, said means varying the bias voltage of succeeding stages over progressively smaller ranges.

' each successive stage, and a common control Iiiv means automatically responsive to Signal amphtude variations for varying all of said means simultaneously. I

15. Areceiver for high frequency signal waves including a detector, at least two tube amplifier stages preceding said detector, an electrondischarge tube rectifier circuit with a signal connection to the detector input, said rectifier circuit including means for developing a direct current potential from signals impressed on the rectifier, and connections from the rectifier circuit means to an input electrode of each stage for iml device is varied at a difi'erent rate.

pressing thereon direct cm'rent control potentials of such difierentmagnitudes as to maintain substantially constant the signal energy supplied to said detector input. Y

16. A receiver for high frequency signal waves 5 including a detector, at least two tube amplifier stages preceding said detector, an electron discharge tube rectifier circuit with a signal connection froma cold electrode thereof to the detector input, means for maintaining the cathode of the rectifier tube positive with respect to said cold electrode, said rectifier circuit including means for developing a direct current potential from signals impressed on the rectifier, and connections from the rectifier circuit means to an input electrode of each stage for impressing thereon direct current control potentials of such different magnitudes as to maintain substantially constant the signal energy supplied to said detector input.

1'1. 'A receiver for high frequency nal waves including a detector, at least two tube amplifier stages preceding said detector, an electron discharge tube rectifier circuit with a signal connection to the detector input, said rectifier circuit 25 including means for developing a direct current potential from signals impressed on the rectifier, and connections from the rectifier circuit means to an input electrode of each stage forimpressing thereon direct current control potentials of such 30 different magnitudes as to maintain substantially constant the signal energy supplied to said detector input and manually controllable means connected to at least'one of the amplifier stages for regulating the maximum signal strength transmitted to said detector.

18. In a system for converting alternating current into uni-directional current of the type comprising a plurality of preceding space discharge devices followed by a rectifier and a.final load v4o circuit, a net work for automatically controlling the transmission efficiencies of said devices comprising a rectifier provided with an alternating current input circuit coupled to the input of said first rectifier, and direct current output circuits 45 connected to ton control elements of said devices from different direct current potential points of said second rectifier circuit in such a manner that the on efiiciency of each 19. In a system for converting alternating current into uni-directional current of the type comprising a plurality of preceding space discharge devices followed by a rectifier and a final load circuit, a network for automatically controlling the transmission eillciencies of said devices comprising a rectifier provided with an alternating current input circuit coupled to the input of said first-rectifier and. direct current output circuits connected to on control elements of on said devices from different direct current potential points of said second rectifier circuit in such a manner that the on efilciency of each device is varied at a different rate and means for predetermining the value of alternating current intensity at which said network starts to function. 20. In a high frequency amplifier system, a plurality of screen grid tubes arranged in cascade, means for supplying at least one of the cold electrodes of each of said tubes with negative energizing potentials progressively decreasing for each successive stage, and a common control means automatically responsive to signal amplitude variations for varying all of said means simultaneously. 1s

21. In a high frequency amplifier system, a plurality of screen grid tubes arranged in cascade, means for supplying a signal control grid electrode of each of said tubes with negative energizing potentials progressively decreasing for each successive stage, and a common control means automatically responsive to signal amplitude variations for varying all of said means simultaneously.

22. In a high frequency amplifier system, a plurality of screen grid tubes arranged in cascade, means for supplying the screen grid electrade of each of said tubes with positive energizing potentials progressively increasing for each successive stage, and a common control means for varying all of said means simultaneously.

23. In a high frequency amplifier system, a

plurality of screen grid tubes arranged in cascade,

means for supplying at least one of the cold electrodes of each of said tubes with positive energizing potentials progressively increasing for each successive stage, and a common control means for varying all of said means simultaneously.

24. In an amplifier system, a plurality of electric discharge devices vhaving grid elements, means for automatically causing biasing potentials to be impressed on said grid elements at unequal rates with respect to each other in response to changes in carrier intensity, the greater rate of change occurring on the grid of the device normally experiencing the least signal potentials.

25. In an amplifying system having a plurality of amplifying stages in tandem, a control circuit comprising an electric discharge device having an input and an output circuit, a resistor in said output circuit associated in varying degrees with the grid circuits of said amplifying stages, the earlier stages being associated in greater degree with said resistor than subsequent stages, whereby a change'in the input circuit of said electron discharge device will produce unequal changes in the amplifier characteristics of said amplifying stages, respectively in proportion to the degree of association.

26. In the operation of an electrical wave amplifier working into a rectifier and subject to signals of varying magnitude, the method of automatically controlling the gain of said amplifier,

which comprises impressing upon the amplifier input circuit two discrete direct current potentials which vary automatically and according to different functions of the magnitude of the incoming electrical wave, one of said potentials being predominately effective for weak signals and the other predominately effective for strong signals.

27. In automatic volume control apparatus wherein two discrete potentials are employed to control amplifier gain, means whereby one of said discrete potentials is obtained by rectification of the amplifier output, and means whereby the second potential is derived from the spaces current flow in the cathode circuit of the amplifier.

28. The method of operation of an electrical wave amplifier so as to secure automatic gain control thereof, which comprises applying to said amplifier a gain control potential which varies automatically with the magnitude of the input of said amplifier and applying to said amplifier a second gain control potential which varies automatically as a function of said first gain control potential.

29. The method of operation of an electrical wave amplifier so as to secure automatic gain to succcessive stages, said voltage variation means said aforementioned circuit elements comprising resistance in the rectifier output circuit, and a I automatically with the magnitudfof thelr'i'put of said amplifier and applying to said amplifier a. second gain control potential which varies auto- 5 matically as a function of said first gain control potential, said second gain control potential being obtained by the voltage drop due to the fiow of current in the cathode circuit of said amplifier. 30. The method of 'operation of a carrier wave amplifier receiving electrical signals of varying magnitudes was to secure an automatic control of the gain of said amplifier, which comprises impressing a direct current potentialgvarying with signal strength upon the input circuit thereof and 15 impressing upon said input circuit a second direct current potential automatically decreasing in magnitude as the strength of the received electric -signals increases, both of said direct current potentials functioningv as gain control voltages. 20

31. "The combination'with a plurality of cascaded amplifier stages whose input circuits are maintained at a common carrier wave frequency,

'of means for varying an amplification-controlling voltage applied to each of said stages, circuit elements in said voltage-variation means for pro'- gressively decreasing the voltage change applied to successive stages, said voltage variation means comprising a tube rectifier, an input circuit for said rectifier shunted across the output of said amplifier stages, connections for supplying the output of said rectifier to the grids of said stages, said aforementioned circuit elements comprising resistance in the rectifier output circuit, and a detector" tube havingits input circuit connected to said amplifier output and the rectifier' input circuit. I

32. The combination with a plurality of cascaded amplifier stages whose input circuits are maintained at a common carrier wave frequency, of means for varying an amplification-controlling voltage applied to each of said stages, circuit elements in said voltage-variation means for pro gressively decreasing the voltage change applied comprising a tube rectifier, an input circuit for. said rectifier shunted across the output of said amplifier stages, connections for supplying the output of said rectifier to the grids of said stages,

detectortube having its input'circuit' connected to said amplifier output and the rectifier input circuit, and means for varying the transmission efiiciency of said rectifier tube.

33. In a high frequency signal transmission system, a plurality of electron discharge tube stages arranged in cascade, means for supplying at least one of the electrodes of each of at least two successive tubes with a positive energizing potential, the potential applied to the second of the successive tubes being the greater in magnitude, means for simultaneously varying the magnitudes of said potentials, the constants of said successive tubes being chosen to cause the changes in amplification thereof to be progressively smaller.

34. In a high frequency signal transmission system, a plurality of electron discharge tube stages arranged in cascade, means for supplying at least one of the electrodes of each of at least two successive tubes with a positive energizing potential, the potential applied to the second of the successive tubes being the greater in magnitude, means for simultaneously varying the magnitudes of said potentials by equal increments, the constants of said successive tubes beingchosentocause-thechangesinamplificationthereoftobep sr flivelynnaller.

35. In ,a high frequency si nal tra system, a plurality of electron discharge tube stages arranged in cascade, means for supplying at least one of the electrodes of each of at least two successive tubes with a positive energizing potential. the potential applied to the second of the successive tubes being the greater in magnitude, means for simultaneously varying the magnitudes of said potentials by progressively increasing increments, the constants of said successive tubes being chosen to cause the changes in amplification thereof to be progressively smaller.

36. In an electrical wave on system employing electron discharge tubes in cascade, the method of controlling the wave tran through said tubes which includes deriving a direct current voltage from the waves which varies in magnitude with the amplitude of the latter, and varying the amplification of the tubes with said voltage so that the amplification of the first tube varies to a greater extent than that of any of the tubes following.

37; In a radio receiver employing electron discharge tubes in cascade, the method which comprises automatically varying the amplification of at least two of the tubes in response to received signal carrier amplitude variations. and simul-. taneously causing the change in amplification of the first of the two tubes to occur at a greater rate.

38. In a radio receiver of the type including means amplifying received signals at radio frequency, a network for deriving from the amplifled signals avvoltage representative of the. signal modulation in still further amplified form, means for further amplifying the amplified modulation representative voltage, means responsive to signal carrier amplitude variations for automatically ad- Justing the amplification or the first means, and an auxiliary manually variable device, connected between said network and the modulation voltageampliiying means, for controlling the trans- 1nili'iistziron or amplified modulation voltage to the 89. In a radio receiver having a demodulator, s apluralityoi'tubesarrangedincascadetotransmit received signals in amplified form to the demodulator input, an audio amplifier, an automatic volume control network constructed and arranged to, vary the gain oi. the first of the cas- 1o cadedtubesto agreaterextentthanthatofthe following tubes, adjustable means other than said network for varying the intensity of the signals transmitted to the demodulator, and means between the demodulator output and said audio amplifier for adjusting the intensity of the audio signals transmitted to the audio amplifier. 7 40. In a radio receiver of the ype ncluding means amplifying received modulated signals at radio frequency, a network for deriving-from the amplified signals a voltage representative of the signal modulation, means for amplifying the mod-' 'ulation representative voltage, means responsive to signal carrier amplitude variations for automatically adjusting the amplification of the first means, and an auxiliary manually variable device, connected between said network and the modulation voltage amplifying means, for con trolling the n of modulation voltage to the latter.

41. In a radio receiver having a demodulator, a plurality of tubes arranged in cascade to transmit received signals in amplified form to the demodulator input, an audio amplifier, an automatic volume control network constructed and arranged to vary the gain of at least one of said cascaded tubes, adjustable means other than said network for varying the intensity of the Signals transmitted to the demodulator, and means between the demodulator output and said audio amplifier for adjusting the intensity of the audio signals transmitted to the audio amplifier.

STUART BALLANTINE.

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