US2020363A - Automatic volume control arrangement - Google Patents

Description

Nov. 12, 1935.r

v. D. LANDON- AUTOMATIC VOLUME CONTROL ARRANGEMENT Filed Aug. 19, 1953 2 Sheets-Sheet 1 vmwrmw w ATToRNEY NOV. 12, 1935. V, D, LANDON 2,029,363

AUTOMATIC VOLUME CONTROL ARRANQEMENT Filed Aug. 19, 1933 2 Sheets-Sheet 2 lNvENToR VERNON D. LANDON ATTORNEY Patented Nov. 12A, 1935 PATENT FPIEy V'AUTOMATIC VOLUME CONTROL ARRANGEMENT Vernon D. Landon, Collingswood, N. J., assignor Yto Radio Corporation of America, a corporation of Delaware Application August 19, 1933, Serial No. 685,965

,- Y 9A Claims.

My present invention relates to gain regulation systems, and more particularly to automatic volume control arrangements for'radio receivers.

It is old in the art to use a separate tube for the 3i-i.. V. C. function of radio receivers. However, this always has involved undesirable complication in the B supply system. It has hitherto been impossible, when using a separate A. V. C. tube, to self -bias or ground all cathodes and have all loi-grid returns' (with no'applied signal) at, or'near,

ground potential. The reason is obvious; the B supply of the A. V. C. tube is in series with the B supply of the RF tubes in all past examples of this system. Either -B is grounded and the RF zcat'nodes placed about 109 volts positive with respect to ground, or the RF cathodes are grounded (or self-biased to ground) placing B Vabout 100 volts negative to ground. Each of these expedients is highly undesirable.

lilly solution of the problem eliminates the necessity of placing the two B supplies in series. True it requires a voltage 100 volts negative to ground. However, this connects only to a portion of the circuit in which hum is easily filtered out due to the high impedance level, and hence the drop across a lter reactor maybe utilized. Hence, the chief object is to obtain the advantage of a separate A. V. C. tube with its fiat A. V. C. characteristic without some of the disadvantages.

Another prime object of my present invention is to provide an automatic volume control arrangement for a radio receiver wherein, unlike automatic volume control systems kn'own in the prior art, the control rectifier tube output electrode is at a positive potential with respect to the cathodes of one or more controlled high frequency amplifiers.

Another important object of the present inven-` tion is to provide in an automatic volume control arrangement for a radio receiver, a Volume control tube whose output electrode is at a positive potential with respect to the cathode of a 'con--V trolled tube preceding the control tube.

(Cl. Z50-20) Y following description taken in connection with wherein like reference characters in the different 10 figures designate similar circuit elements, there is shown in Fig. 1 a conventional form of superheterodyne receiver embodying one form ,of the invention. While the invention is disclosed in connection with a superheterodyne receiver, it 15 is to be clearly understood that the receiver can be of the cascaded tuned radio frequency amplilier type. The various circuits of the superheterodyne receiver will only be described briefly since those skilled in the art are well awarerof 20 the specific connections of a superheterodyne receiver of the type shown in Fig. l.

A signal collecting means, such as a grounded antenna circuit A, is coupled to the tunable input circuit I of a radio frequency ampliiier 2 whose 25 gain is to be automatically regulated. The tubeV 2 is of the radio frequency pentode type, and known as a 58 tube, the anode circuit of the tube being coupled to a tunable input circuit 3 of the first detector tube 4. The rst detector tube is also of 30 the pentode type, and, with the succeeding intermediate frequency amplier tube 5, is of the 58 type.

'Ihe local oscillator 6 of the receiver is conventionally shown, its tunable circuit 1 being repre- 35 v sented as including a variable tuning condenser, which variable tuning condenser is uni-controlled with the variable tuning condensers of circuits 2 and 3, this being represented by the dotted lines 8. In the anode circuit of the pentode rst detector 4o tube there is included a network 9 resonant to the opertaing intermediate frequency, this network 9 being coupled to a similar network 9', also tuned operating intermediate frequency, this network 9 being disposed in the grid circuit of the inter- 45 mediate frequency amplifier 5. A line I9 represents the connections between the local oscillator 5 and the cathode circuit of the first detector tube and it is to be understood that this numeral i9 designates the conventional connections which 5o',A

couple the local oscillator and lirst detector.

The anode circuit of the tube 5 includes a resonant circuit l I tuned to the intermediate frequency, the intermediate frequency energy in the circuit Il lbeing fedv to two paths. One of 55;;

these paths, represented by the numeral I2, includes the second detector and succeeding audio frequency network, the circuits connected to the path I2 being omitted to preserve simplicity of disclosure. The second path to which the intormediate frequency energy of network II is fed, includes the circuit I3, tuned to the intermediate frequency, and coupled to circuit II. The automatic volume control tube is designated by the numeral I4, and the circuit I3 is disposed in the grid circuit of tube I4, the latter being a tube including independent diode and pentode sections and is of the 2B7 type.

The circuits described up to this point are generally well known to those skilled in the art, and it will be recognized that the tube I4 functions as a source of direct current control potential for regulating the gain of the radio frequency amplifier tube 2, the first detector tube 4 and the intermediate frequency amplifier tube 5. In systems known heretofore the anode of the control tube I4 has been at a negative potential with respect to the cathodes of the controlled tubes. However, by means of the present invention these controlled tubes have their cathodes at a negative potential with respect to the output electrode of the control rectifier.

Furthermore, the present system of automatic volume control is accomplished in a practical and easily manufactured circuit, and with a minimum of auxiliary circuit elements. This is accomplished by connecting the anode of tube I4 to the low potential side of resistor R1 of the power source bleeder through a lead I5. The high potential side of resistor R1 is connected to the positive terminal of the positive potential supply source, this source being omitted, but it being clearly understood that it may be the usual filtered rectified alternating current source, or even a direct current source. The negative side of the potential supply source is represented by the symbol (-B) and the negative side of the bleeder is connected to the -B terminal through a path which includes the lead I6 and I6. The bleeder comprises four resistors in series, these being designated as R1, R2, R3, an-d R4. A practical set of values for these resistors, it being emphasized that these values are merely illustrative, are as follows:

R1=30O,000 ohms; R2=180,000 ohms; R3=6,000 ohms; R4=194,000 ohms.

The junction of resistors R1 and R2 is designated as being of a value of volts, the junction between resistors R2 and R3 is designated as having a potential of 0 Volts, while the junction of resistors R3 and R4 has a value of 3 volts, and the negative side of resistor R4 has a potential value of -100 volts.

The diode anode of control tube I4 is connected by a lead I'I to the junction of resistors R2 and Re., and therefore this diode anode is at zero volt potential, or at ground potential. The automatic gain regulation path, designated A. V. C. includes a lead I9 having one terminal thereof connected to the junction of resistors R3 and R4, the lead I9 being connected to the grid circuits of tubes 2, 4 and 5 through resistors 25, 2I and 22 respectively. Appropriate radio frequency by-pass condensers are connected between the grid and cathode electrodes of each of tubes 2, 4 and 5, and the usual common cathode potential supply connection is made to the anodes of tubes 2, 4, and 5 through lead 23.

The anode of control tube I4 is connected by lead I5 to a point of +100 volts on the supplyA bleeder, while the anodes of the preceding tubes are supplied with a potential of 250 volts. Proper screen grid potential is secured for the tubes by connecting a secondary bleeder resistor R5 between lead 23 and ground, and then connecting 5 the lead 24 between the screen grid leads of tubes 2, 4 and 5, and point a on bleeder R5. The lead 25 connects the screen grid of tube I4 to point b on bleeder R5, this point being at a less positive potential than point a.. The control grid of tube 10 I4 is connected through tuned circuit I3 and lead 25 to a point intermediate resistors Rs and R7, one side of resistor R7 being connected to lead I6 and the -B terminal, while one side of resistor Re is connected to the grounded cathode l5 of tube I4.

The resistors R1, R2, R3, R4 are so proportioned as to give the indicated voltages to ground when the control tube I4 is cut off, and this is the normal Zero signal condition. When a very 20 strong signal is tuned in the potential values. associated with these last named resistors become respectively +2,50 volts, +20 Volts, 40 volts, 43 volts, and 100 volts, eiectively approaching cut-off of the radio frequency tubes. 25 Of course, a moderately strong signal will only partially cut olf the controlled tubes in the manner usual to automatic volume control systems.

It will be observed that an accurate balance is required between the values of R1, R2 and R4, 30 to prevent the voltages marked zero volts and -3 volts from varying badly under zero signal conditions. To remove this diliiculty, the resistors are first calculated on a voltage divider basis as indicated. The value of R2 is then deu creased l0 or 15 per cent. This would cause the Voltage on the positive terminal of R3 (0 V. point) to rise to possibly 10 volts positive if the diode connection were not present. In fact, the voltages remain practically unchanged because 40 of the diode current which flows when the diode plate is very slightly positive. Each of the resistors may now be varied over moderate limits without affecting the bias on the amplifier tubes appreciably. About one-half mil of plate current 45 in the automatic volume control tube would be required to cut oi the amplifier tubes plate current in this preferred embodiment.

When the diode connection is made, the potential of the positive end of R3 becomes the same 50 u as ground potential within one or two tenths of a volt due to the diode current which flows. Moderate variations in the valuesof R1, R2 and R4 now cause unappreciable variations in the potentials of the terminals of R3 to ground. When a signal is 59V applied, the A. V. C. tube does not start to function until the signal amplitude reaches a predetermined value of several volts on the grid of the A. V. C. tube. Plate current then flows, increasing the current in R1 and decreasing that in Rz, 60 R3 and R4. The potentials of the terminals of Ra cause negative biasing off of the radio frequency ampliiiers just suflicient to maintain the radio frequency voltage applied to the A. V. C. tube at the desired value over a wide range of input 65 amplitudes.

In Fig. 1 the .automatic volume control tube is shown actuated with intermediate frequency on its grid. By adjusting the ratio of screen voltage to bias voltage, the intermediate frequency 70 voltage required to barely start plate current may be adjusted to any desirable value such as 10 volts of intermediate frequency. Increasing this one or two more volts will be sufficient to cut off thevradio frequency tubes. Hence, a very flat 'l5-vv' curve will be obtained, of radio frequency input to Y Y the receiver versus audio output; It is sometimes desirable to keep intermediate frequency out of the automatic volume control tube to prevent the intermediate frequency harmonics being fed back to the input circuit. This makes `it desirable to actuate the automatic volume control tube with direct current.

In Fig. 2 there is shown a circuit arrangement for actuating the automatic volume control tube with a direct current component. As in the case of Fig. 1 the power potential supply source is not shown, but the leads and 3l are to be understood as connected to the +B and B terminals of the power potential source. 'ITne resonant circuits I! and i3, which were described in connection withFig. l as tuned to Vthe operating intermediate frequency, are connected between the intermediate frequency amplifier network and the second detector. networks preceding circuit i l are similar to those shown in Fig. l preceding Vthe circuit H therein. The second detector tube is of the type known as an 85 tube, and is of the duplex diode pentode type. .That is to say, the tube 32 includes a pentode section independent of a pair of diode sections. This type of tube is now well known to those skilled in the art, and most generally comprises a common cathode sleeve for the diode and pentode sections, the diode anodes 33 in the present case being strapped together and connected to the high potential -side of circuit I3.

The cathode is connected to tlie low potential side of circuit i3 through a resistor 3d shunted by a condenser 35, the control grid of the pentode section being connected by lead 36 to the ungrounded side of resistor 313. The electron stream from the cathode 3@ to the electrodes of the pentode section of tube 32 is `independent of the electron stream fiowing to the diode anodes 33. For this reason the tube 32 functions in a dual capacity. One of these capacities'comprises diode rectification for second detection, while the other capacity comprises pentode ampliiication, of the audio frequency component of the second detection step. The audio frequency amplifier network usually connected to theA output electrode of the pentode section oi tube 32 is not shown, but the circuit necessary for the utilization of the direct current component of the pentode section output is shown.

The automatic volume control tube is of the pentode type, as in Fig. l, and has its control grid connected to the anode of the pentode section of tube 32 through a path which includes lead 4I, resistor l2 and lead 43. The lead d3 is connected to the positive potential lead 3U through a resistor 43. The low potentialV side of resistor 42 is connected to the negative potential lead 3| through a resistor 44, the less negative side of resistor M being at a potential of about -15 volts. The ground lead I8 is connected to the cathode 3B of tube 32 through a' bias resistor R8, but'it is to be noted that if the diode second detector does not have to be maintained at a positive potential, the detector cathode resistor R8 may be omitted.

The bleeder R1, R2, R3, and R4 is employed as in Fig. l the anode of tube d@ being connected to the junctions of resistors R1 and Rz, the zero volt side of resistor R3 being connected, as in Fig. 1, through lead l1 to the suppressor grid of the radio frequency amplifier tube .2. The automatic Volume control lead le is connected to the -3 volt point of resistor R4 as in Fig. 1, the remaining connections being the same as in this last named It will be understood that theV figure. The screen Vgrid potential for tube is derived from the junction of resistors 59 and 5l, the latter resistors being connected in series between leads 3@ Vand I'.

The control grid of the tube 4@ is rmaintained 54 well below cut-off since the, voltage divider is disposed in the plate circuit of the detector tube 32, this arrangement being similar to that employed in Fig. l. Hence, any moderate change in the values of the detector plate resistors simply 10 changes by a slight amount the values of bias change required to begin to actuate the automatic Volume control tube. It should be noted that in Fig. 2 all the elements of both tubes, except the control grid of tube lill, are at all times positive l5 with respect to ground. The cathodes of the signal amplifier tubes, as shown in Fig. l, are of course grounded.

While I have indicated and described several systems for cariying my invention into effect, it 20. f

output electrode of said control tube to a point 30.

of positive potential on said divider, an amplifier gain control connection conductively connecting the signal control grid of said amplifier to a point on said divider which is negative with respect to said rst point, means for maintaining the catli- 35..

odes of the amplifier and control tube at a common voltage which is intermediate the voltage of said two points, and means for transferring amplified signal energy from said signal ampliiier to the input circuit of said control tube. 40

2. In combination, a signal amplier, a control tube for regulating the amplifier gain, a voltage divider, means for connecting the output electrode of said control tube to a point of positive potential on said divider, a gain control connec- 45 tion conductively connecting the signal control grid of said amplifier to a point on said divider which is negative with respect to said iirst point, means for transferring amplifier signal energy from said signal amplifier to the input circuit of said control tube, means for maintaining the amplii'ier and control tube cathodes at a common positive Voltage with respect to the amplifier grid, and means for connecting the control grid of the conf trol tube to a point in the divider circuit of such negative potential that the control tube is cut oi in the absence of signal energy.

3. An automatic volume control for a receiver, the latter including at least one signal amplifier provided with a tube having a cathode, an anode and a control grid, said control comprising a succeeding control tube provided with a cathode, control grid and plate, means for coupling the grid of the control tube and the anode circuit of the 'preceding amplifier, a commo-n source of direct current voltage for the ampliiier and control tube, means for establishing the cathodes of the amplifier and control tube at a common voltage, a gain control connection from the ampliiier grid to a point on said source which is at a predetermined negative voltage with respect to a second point on the said source, said second point being at a voltage equal to that of said common voltage, a connection from the control tube anode to a third point on said source which is positive with respect to the first two points.

4. In a system as defined in claim 3, a connection from the said cathodes to the negative terminal of said source.

5. In a system as dened in claim 3, means in the space current path of the control tube for maintaining the control tube grid at out-off voltage in the absence of received signals.

6. In a system as defined in claim 3, an auxiliary anode in the control tube, and a connection from the auxiliary anode to said second point on the voltage source.

7. An automatic volume control for a receiver, the latter including at least one signal amplier provided with a tube having a cathode, an anode and a control grid, said control comprising a succeeding control tube provided with a cathode, control grid and plate, means for coupling the Vgrid of the control tube and the anode circuit of the preceding amplier, a common source of direct current voltage for the amplifier and control tube, means for establishing the catho-des of the amplier and control tube at a common voltage, a gain control connection from the amplier grid to a point on said source which is at a predetermined negative voltage with respect to a second point on the said source, said second point being at a voltage equal to that of said common voltage, a connection from the control tube anode to a third point on said source which is positive with respect to the first two points, said voltage source comprising a plurality of resistor elements arranged in the space current path of the control tube, the voltages of the rst and second points become increasingly negative with signal amplitude increase, and the voltage of the third point becomes less positive.

8. An automatic volume control for a receiver, the latter including at least one signal amplier provided with a tube having a cathode, an anode and a control grid, said control comprising a succeeding control tube provided with a cathode, control grid and plate, means for coupling the grid of the control tube and the anode circuit of the prece-ding amplifier, a common source of direct current voltage for the amplifier and control tube, said source comprising a plurality of resistors arranged in series in the control tube space current path, means for establishing the cathodes of the amplifier and control tube at a common voltage, a gain control connection from the amplier grid to a point on said source which is at a predetermined negative voltage With respect to a second point on the said source, said second point being at a voltage equal to that of said common voltage, a connection from the control tube anode to a third point on said source which is positive with respect to the first two points, and an additional signal amplier, interposed betweeri the first amplifier and control tube, and having its cathode at the said common voltage and its grid connected to the said rst point.

9. An automatic volume control for a receiver, the latter including at least one signal amplifier provided with a tube having a cathode, an anode and a control grid, said control comprising a succeeding control tube provided with a cathode, control grid and. plate, means for coupling the grid of the control tube and the anode circuit of the preceding amplier, a common source of direct current voltage for the amplifier and control tube, means for establishing the cathodes of the amplifier and control tube at a common voltage, a gain control connection from the amplifier grid to a point on said source which is at a predetermined negative voltage with respect to a second point on the said source, said second point being at a voltage equal to that of said common voltage, a connection from the control tube anode to a third point on said source which is positive with respect to the rst two points, said voltage source comprising a resistive potentiometer arranged in the control tube plate circuit, and a signal demodulator coupled to the amplier anode circuit.

VERNON D. LANDON.

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