US2144601A - Automatic volume control circuit - Google Patents

Description

Jan. 24, 1939. ANDREATTA 2,144,601

AUTOMATIC VOLUME CONTROL CIRCUIT I Filed NOV. 30, 1935 75 1NVEZ\TOR. AL FONS ANDREATTA ATTORNEY.

Patented Jan. 24, 1939 v NETED STATES PATENT OFFIQE AUTOIVIATIC VOLUDIE CONTROL CIRCUIT Alfons Andreatta, Berlin, Germany, assignor to Allgemeine Elektricitatz Gesellschaft, Berlin, Germany Application November 30, 19-35, Serial No. 52,323

In Germany February 20, 1935 1 Claim. (Cl. 250-20) Automatic volume control in radio apparatus stance, O to 6 volts. As already pointed out above is obtained, in g neral, in that the grid bias of only one half of the control potential is used for amplifier, or detector, tubes is varied in relation the control of grid 8. If the bias of tube at to the high frequency potential applied to the zero control potential is equal to 1 volt, there '5 input of the receiver. The tubes in this case thus appears at grid 8 a variation of l to 4 5 are so constructed that various grid biasing povolts, and at grid 6 a variation of -1 to '7 volts. tentials correspond to different degrees of am- In order to obtain a Wide range of control it is plification. In the drawing, the usual circuit is desirable to utilize fully these voltages for the represented in Fig. 1. Figs. 2 and 3 show the control. However, this cannot be done in the 10 two different modifications of the invention. circuit shown, since the Voltage drop at resistor 10 The control potential at resistor 2 and pro- 9 is in opposition to the control potential. It is duced by tube l is applied, across resistors 3 and necessary to provide a. bias of, for instance, 3 to the first control grid 6 and across resistor volts at the biasing resistor ll] of tube I in view I to the second control grid 3 of tube 5. In the of the considerable tone frequency potential at circuit shown, grid 8 is not supplied by the entire the grid of the tube. 15 control potential, but receives only a part thereof At the control potential 6 volts, grid 6 has a for instance one half of the control potential. potential of 6 (resistor 2) +3 (resistor Ill) 1 A resistor Q through which a voltage drop is (res to 9) VO- 3 has the potential produced by the cathode current, supplies a fur- 3 (from resistor 2) +3 (resistor l9) 1 (resistor ther grid bias for the tube 5. The tube 5 has 9) 1 volt. In place of a control of 1 to 7, 20 three biasing potentials applied: or 1 to 3 volts there occurs a control in the (l) A negative bias derived from the resistor range from -4 to 1 or 0 volt, i. e. the control 9 d whose lu depends upon the c th de fails at the second grid. It, therefore, follows Current that despite the considerable number of elements (2) The control potential at resistor 2 which is nd de pite the co trol of two d an ent y 25 like ise negative. unsatisfactory control will be obtained with the (3) A positive bias at resistor H! which techknown circuit, and which is far from sufficient nically cannot be suppressed and which is in for compen g most of the fadi p e wmenaopposition to the potentials I and 2. The aforementioned drawback is overcome by Ordinarily, the resistors are so dimensioned the automatic volume control circuit described 30 that at a control potential equal to zero, both in the following. With this circuit it is possible grids of t tube m b cgntrglled h a l negato attain the widest possible control determined tive bias of, for instance, one volt impressed by the exponential characteristic of the tube or thereon in order to prevent grid current. This is tubes s and y the Control Potential produced accomplished by increasing the Voltage drop at at resistor 2. In the new circuit the direct cur- 35 resistor s by, for instance, one volt above that n w through r i or 9 is maintained conat resistor it. If a high-frequency potential is stant so that also a constant voltage drop through applied to the input resistor 4 Which is amplified t e es t W be produced. The direct current in the tube 5 and detected in the diode path ll, Potential pp aring at resistor I0 is constant as the grid potentials of tube 5 become negative in aforementioned. The negative grid bias results 40 View of the control potential appearing at the from the difference of the direct current potenresistor 2. tials produced at resistor 9 and at resistor H],

Consequently. 3118 P te current of tube 5 Will be in addition to the control potential at resistor 2. decreased AS a result thereof there occurs a Since in view of the arrangement of the circuit,

further Q -i f the girld Voltage of tube the potentials at the resistors 9 and Ill are connamfly P f that as a result of the stant, the variation of the negative grid biasing flecrrcase p f Current the voltage q potential depends only upon the potential at rethrough the resistor 9 becomes smaller. As will t 2 th t a t 1 b be seen from the following data, this voltage or so a m Xlmum con m w} e variation is undesirable, since it acts against the a In the example of the calcplatlon aboYe 50 control potential and decreases the range of acglven there Wonk} 1n fact be obtained for gnd 6 a control potential of l to '7 volts (as comticn of the control.

It will be assumed that the available variation pared Wlth to volts 0f the hltherto known of the high-frequency potential at resistor 4 proarran nt), a r grid 8 a control p ntial 55 duces at resistor 2 a control potential of, for inof l to 4 volts-(in the hitherto known ar- 55 rangement no control at all was obtained through rid 8).

The circuit diagrams 2 and 3 show examples for the practical application of the invention. In the circuit of Fig. 2, the emission current of the end tube is at the same time passed as additional direct current through the resistor 9 whereby practically a constant voltage drop through resistor 9 is obtained since the emission current of the end tube is larger by one order than the emission current of tube 5.

The plate current of end tubes as used at this time in radio apparatus with volume control is approximately 40 mA, and the plate current of a controlled tube is 3 to 4 mA. While in the above example the voltage at resistor 9 fluctuates on account of the cathode current Within the limits between 0 and 3 volts, the voltage produced by the cathode current remains practically constant when applying the invention. Those skilled in the art will realize that resistor 9 should have its re-- sistance reduced to a value such that the total current flow therethrough will provide the desired normal operating bias for the grid 6.

A further example of applying the invention is shown in Fig. 3. In this circuit a practically constant voltage drop is produced through the resistor 9 by the additional current of the voltage divider of the screen grid. This is accomplished in that the screen grid potentiometer consisting of the resistors l2 and i 3 is not grounded at the pole as is usually done, but is placed at the cathode of the tube 5 so that the potentiometer lies in series to the resistor 9. The extent to which the basic voltages existing at resistor 9 shall be independent of the cathode current of tube 5 simply depends upon a corresponding dimensioning of the resistors l2 and I 3.

The automatic volume control according to the invention, may also be obtained in another way, for instance, the exciting current of the field coil of a dynamic loudspeaker may be passed through the resistor 9. This has for its effect an especially great independence from the cathode current of tube 5 since the latter is only & of the exciting current.

What is claimed is:

In a radio receiver comprising at least one sig nal transmission tube provided with at least a signal input electrode, a cathode and an output electrode, an impedance in the space current path of the tube developing a first direct current voltage, a signal rectifier including an impedance in its space current path for developing a second direct current voltage which varies in magnitude with the signal amplitude, a source of direct cur rent voltage of relatively fixed magnitude, said signal input electrode being connected to said cathode through an automatic gain control path including at least a portion of said rectifier impedance, said fixed source and at least a portion of said first impedance arranged in series relation, the voltage of said fixed source being in polarity opposition to the first and second direct current voltages and the latter two voltages biasing said signal input electrode negatively, and means for maintaining said first voltage substantially independent of the changes in negative bias of said signal input electrode, said means comprising a direct current source connected to said first impedance in such a manner that the current thereof flows through the impedance, the magnitude of the last source being sufficiently greater than that of the transmission tube space current that the said first direct current voltage remains substantially constant in value.

ALFONS ANDREATTA.

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