US2067033A - Electrical rectifier and detector system - Google Patents

Description

1937- s. Y. WHITE I 2,067,033

' ELECTRICAL RECTIFIER AND DETECTOR SYSTEM Originl Filed July 29, 1929 3 Sheets-Sheet l INVENTOR Afikinez Y Willie ATTORN V Jan. 5, 1937. s. Y. WHITE 2,057,033

ELECTRICAL RECTIFIER AND DETECTOR SYSTEM Original Filed July 29, 1929 3 Sheets-Sheet 2 a r I I I INVENTOR 2 sla 15mm ATTORNE Jail. 5, 1937. 5, wHlTE 2,067,033

. ELECTRICAL RECTIFIER AND DETECTOR SYSTEM Original Fild July 29, 1929 s Sheets-Sheet s INVENTOR ,szdm KW/u'ie BY v I Patented Jan. 5, 193'? UNITED STAT ELECTRICAL RECTIFIER AND. on'rno'roa SYSTEM Sidney Y. White, New

York, N. Y assignor, by

mcsne assignments, to Radio Corporation of America, New York, Delaware N.'Y., a corporation of 8 Claims.

My present invention relates to electrical systems, and in particular electrical systems involving alternating current rectification, high frequency signal current detection and like effects.

My present application for Letters Patent is a continuation in part of the application for my United States Letters Patent No. 1,789,664, granted 20 January 1931, and is a division of my copending application for United States Letters Patent filed 29 July 1929, Serial Number 381,754.

A particular object of my invention is employing cascaded electron tubes with connections and modes of energizing and operating making possible novel and useful signal and other alternating current rectifying and detecting effects.

Many of the physical details and operating featuresof the systems herein'disclosed are extensively illustrated, described and commented upon in my aforesaid patent and co-pending applica- 20 tion, so that reference to these prior exposes may facilitate understanding the present inventionfrom its herein following description in connection with the various figures of the accompanying drawings.

Fig. 1 diagrammatically illustrates a cascaded electron tube system of an uneven number of tubes including connections and elements for employing features of my invention.

Fig. 2 diagrammatically illustrates a cascaded O electron tube system of an uneven number of tubes having various details and elements differing from Fig. 1.

Fig. 3 includes modifications of the details and elements of Figs. 1 and 2.

Figs. 4 and 5 are systems of an even number of tubes differing from each other in details and elements.

Figs. 6 and 7 are additional systems including features of: my invention effected in novel ways.

Fig. 8 serves as a graphic aid to explanation of a useful feature of my invention.

Referring to Fig. 1, element VT1, VTz and VTs are triple electrode electron tubes connected in cascade in direct-coupled fashion through coupling resistances R2 and R3, the anodes of the several tubes being energized by the batteries B1, B2 and B3, connected and poled as shown. The filaments are heated by current from battery A1 connected and poled in a conventional manner as shown. The output circuit of tube VTs includes a translating device LS in series with a condenser C3 and in shunt to a choke coil CH, one conventional arrangement.

The anode energizing circuit of output tube VTa returns to its filament by way of resistance RC included in the input circuit of the leading my aforementioned patent and co -pending appli-v cation, which result is, however, not a primary feature of my present invention.

Since the system is of direct-coupled nature, it is apparent that alteration of potential in preceding elements of the system will carry through to the output of the system; for example, a change in potential of the grid of tube VT1 will change the anode current of tube V'Is, as will a change in electron emission from the filament of tube VT1 and other like possible changes of state in the system.

It is obvious that if the amplifying ability of the system is large the overall displacement effect from one end of the system to the other Will be correspondingly large, so much so that a relatively insignificant change of potential on the grid of tube VT1 may cause the anode current of the tube to leave entirely the straight portion of the output current characteristic; curve, a usually intolerable adjustment for such practices as faithful reproduction of audio frequency currents.

It is seen, however, that any change in the anode current of tube VT3 will develop a corresponding change in the potential across resistance Re, which change in potential is impressed upon the grid of tube VT1 and, being a series of an odd number of tubes in cascade the polarity of the developed potential is opposed to the effect tending to change the anode current of the tube V'I's. In other words, the arrangement acts to'stabilize the system, it being possible with proper adjustment to maintain the operation substantially around the mid-point of the anode current characteristic of the output tube VTs even with a system of very high amplifying ability having fairly large disturbing changes of potential impressed upon the grid electrode of tube VT1.

It is well known that the impressing of alternating electrical currents on the grid of a three electrode type of tube has the effect of developing a negative potential on the grid, particularly in the case of such tubes so energized as to rectify the impressed alternating currents, the effect being particularly evident in the case of high frequency currents of the order generally used in radio practice, the amount of biasing effect being proportional to the intensity of the impressed alternating currents.

Referring to Fig. 1, it is seen that the biasing potentials impressed upon the grids of tubes VT2 and VT: depend upon the values of the direct current components flowing through resistances R2 and R3, respectively; that is, the anode currents of the preceding tubes. It is apparent that if there is a rectification effect in tube VT1 the normal anode current of this tube will be modified by the rectified component, so that the normal bias on the grid of tube VT2 will be modified to the extent that the anode current flowing through coupling resistance R2 is modified by the rectified component of the incoming alternating currents.

The normal plate current or anode current of tube VTa, flowing through resistance Re, establishes an initial negative potential for input tube VT1 in accordance with the usual practice of initially negatively biasing the grid of the input tube. For faithful reproduction, it is desirable to have the initial biasing potential of greater value than the amplitude of the incoming alternating currents in order that the incoming currents can at no time change the resultant potential to a positive nature. However, the tube is more sensitive to weak incoming signal currents when weakly biased than when strongly biased, but should be strongly biased when occasion for receiving strong incoming signals arises, in order not to bring in the effect of having the grid swung to a positive potential by the incoming signal energy. The system of Fig. 1 is automatically capable of bringing about these desirable conditions through proper adjustment of the degrees of the actions herein referred to. Assume that the value of resistance Re is so chosen that the normal anode current of tube VTx develops an initial bias for the grid of tube VTl, resistance Re can be so chosen that as the bias effect on the grid of tube VTI is increased by increased incoming strength of signal, the biasing potential developed in resistance Re is not increasing at the same rate, so that the difference between the potentials increases, to leave an increasing biasing potential for the grid of tube VT1 with increase of strength of incoming signal current. In other words, the system can be made highly sensitive to incoming weak signals, and to automatically adjust itself to have adequate biasing potential for incoming strong signals.

If the compensation is not complete, it is apparent that the anode current of the output tube will not remain at the mid-point of its characteristic curve, but will drift away from this point. However it is possible to arrange the system so that for weak incoming signals the anode current of the output tube is not at the mid-point, but will be pulled into a mid-point position for the strongest signals, for under these conditions the full length of the straight portion of the characteristic curve is needed more than when the incoming signals are weak.

In Fig. 2, I again show three triple electrode tubes connected in cascade relation by way of direct-coupling as in Fig. 1. In this case I show the tubes of the indirectly heated cathode type in locations VT"1 and VT"2, the heaters being heated in parallel with the filament of tube VT:

through the secondary winding S3 of transformer PT. I show a conventional rectifier and filter system for energizing the cold electrodes of the tube including potentials taken from a potentiometer resistance PR. The power rectifier is shown as a tube RT designed for full wave rectification, the tube being energized from an alternating current source AC through transformer PT and secondary windings S1 and S2. The filter system comprises the filter condensers F01 and F02 connected across the terminals of filter inductance FL, the negative side of the system being grounded at X. The current for the heaters of tubes VT"1 and VT"2 is reduced in po tential below that of the filament of VT; by a resistance RF.

The input to the system is shown to have a switch SW5 for selecting as an input source either the phonograph pick-up PU through a potentiometer resistance RP, or a high frequency signal input through transformer T and tunable circuit including condenser TC, the condenser C2 constituting a signal current by-pass condenser.

The potentiometer resistance PR may be made to pass practically only the anode current of the output tube VT3 by making that portion of the potentiometer between the points (1 and e very large in resistance value compared to that portion between points a and b, thus substantially limiting the current drain on the filter system to that maximum current required for the anode circuit of the output tube. The connections of coupling resistances R2 and R3 to potential points 0 and d respectively in potentiometer resistance PR takes the place as potential sources of the batteries B1 and B2 in Fig. 1.

As a stabilizer and adjuster of the grid potential of the input tube VT"1 I employ the thermionic tube VT4 connected as shown. The current in potentiometer resistance PR, and therefore the anode current of output tube VTs, is caused to flow through the filament of stabilizer tube VT4, the filament of the tube being chosen so that the heating had by the normal current maintains the filament on the verge of electron emission. The result is any change in the anode current of output tube VT3 will change the electron emission in stabilizer tube VT4, and therefore the conductivity of its space charge path between filament and anode, a three electrode tube being shown with the grid and plate elements tied together to form the anode. The anode is energized by the potential between points a and b, so that any change of the space charge path impedance will change the amount of current fiow through the path and therefore resistance R connected in series with the path. Resistance R is connected in the input circuit of tube VT1, and therefore the potential developed therein is applied to the grid electrode of tube VT"1.

It is thus seen that with the aid of this electronic arrangement any tendency of the anode current of the output tube VT3 to change with any degree of permanency may be offset by the change in electronic emission developing the amount of desired potential change in potential developing resistance R. Since the rate of change of temperature of a filament is low compared to the rate of change of signal current, it is apparcut that signal current changes in the output of tube VTs will be little affected by the stabilizing arrangement; whereas, any attempted permanent change will be affected. This is an advantage over the arrangement in Fig. 1 in that the resistanceRc inqFig. 1 introduces additionally regenerative feed-back of signal currents.

Obviouslythe sameadjustment for changing the grid bias potential with change of signalcurrent-intensity as pointed out in connection with Fig. 1 can be made in the arrangement of Fig. 2. In Fig. 3 an arrangement for stabilizing and controlling the degree of biasing potential of the carrying the anode current of the output tube VT3, is supplemented by a high resistance PR1. The result is that any change in the anode current of output tube VTs will be appreciably manitested in potentiometer resistance PR and not in high resistance PR1. The filament of input tube VT1 is connected to a point b in potentiometer resistance PR, while the grid of this tube is connected to a point b in resistance PR1, so that the normal grid bias potential of input tube VT1 is the difference of potential in the two portions of the resistances a and b and a and b. This differencecan be made normally negative for initial biasing of input tube VT1 by choosing a desired negative difference between the potentials of the two portions mentioned. The result is, any change in the anode current of output tube VT: will noticeably change the difference of potential across points a and b, and little change the potential across points a/ and I), thus changing thebiasing potential on the grid electrode of input tube VTl. As stated as to the previous fig-- ures, the adjustment can be made to give any desired rate of increase of biasing potential for the grid of input tube VT1 in proportion to strength of incoming signal current as may be desired. The switches SW10 and SWm indicate how the coupling resistances R2 and R3 may be connected for energizing to points of potential in either the potentiometer resistance PR, or its supplemental resistance PR1.

Fig. 4 is a cascade arrangement comprising tWo triple electrode tubes having the same form of stabilizing arrangement as that employed in Fig. 3. However, since Fig. 4 is of the even numbered type tube, it is necessary to reverse the polarity of the stabilizingaction, so that in, this case the filament of tube VT1 is connected to the point I) on resistance PR1 and the grid of the corresponding tube is connected to potential point b on resistance PR.

. Fig. 5 corresponds to Fig. l except in the matterof the stabilizing'feature, dependence being had in the Fig. 5 arrangement upon the variation in resistance of a heated filament, such as the filament of an incandescent lamp, with temperature. Lamp LP is shown inserted in. series with resistance PR, which resistance is preferably selected to be of such value with respect to supplemental resistance PR1, as to conduct the main body of the anode current of output tube VTz, so that variations in the output current of this tube will change the temperature of the heated filament, thereby changing the potential differ ence between points a and l) differently from the amount of potential change between points a and I), thus bringing about a desired change in the grid biasing potential of input tube VT1.

Thisarr'angement has a desirable result in that the changing of the temperature of the filament of the lamp LP cannot take place rapidly enough to respond to the frequencies of usual signal currents, but will respond to any tendency towards prolonged change in the anode current of the output tube.

Fig. 6 includes a simple but decidedly effective way of bringing about the stabilizing effect of control of input tube grid bias. Two tubes are shown in direct-coupled cascade, the input tube V1 being shown as of the screen-grid type; that is, including an electrode arrangedto electrostatically isolate the anode and control electrodes. The coupling resistance R2 is shown connected to the positive side of the source SF through a 1 high resistanceRz, there being a signal current by-pass condenser Cc connecting the filament to a point intermediate these resistances. A signal current by-pass condenser Ca is connected in shunt to potentiometer resistance PR to lessen the amount of signal current potential developed in resistance PR, this being helpful to lessen signal current feed-back effects.

A resistance R11 is shown connected between the cathode and the point I), so that both the anode current and the screen-grid current of tube V1 flow through this resistance to' develop a. potential therein. This resistance is selected of sufliciently high value to develop rather a. substantial value of negative potential with respect to the control electrode of tube V1; that is. considerably higher than needed for normal operation. This excess of potential is in large part neutralized by the opposing positive potential had by connecting the grid of tube V1 to the point of positive potential 7c in potentiometer resistance PR. There is, therefore, a differential effect in the changing of the resultant biasing potential on the control clectrol on the tube V1 with change of intensity of incoming signal current, making for very positive and certain stabilizing and grid biasing action. The screen-grid of tube V1 is positively energized as usual by connecting to the positive point 8 on. potentiometer resistance PR.

Fig. 7 shows the differential eifect applied to the usual transformer-coupled type of system. In this form of system the feature of stabilizing is not needed as the transformer coupling prevents direct current effects from being transferred throughout the system, but is useful in changing the biasing potential of the input tube to conform with changes in intensity of the incoming signal currents.

In Fig. 7 the tube D is the usual three-electrode type used as a detector for high frequency currents impressed through tunable circuit TO, the condensers C2 and C"3 being the usual signal current by-pass condensers. The detector stage is shown coupled to an amplifying stage including tube VT2 through a transformer AT, the output circuit of the tube VT2 being coupled to a translating device LS through a transformer OT. Condensers C9 and C3 are the usual signal current by-pass condensers. tubes are shown energized by connections to the source SF, the potential on the anode of the detector tube D being suitably reduced by series resistance R13. The resistance R12 in series with the anode circuit of tube VTz develops a potential which is applied as a biasing potential for the control electrode of tube VT2. A suitable part of this potential is used to oppose a large potential developed in resistance R11 in the anode- The anodes of the two cathode circuit of detector tube D, so that any change of current in the detector anode circuit due to rectification of incoming signal current changes the potential across resistance R11 to create a substantial difference over the opposing fixed potential obtained from resistance R12, the resulting percentage change on the control electrode of detector tube D being greater than is the percentage change in the potential developed in resistance R11 alone.

Fig. 8 graphically shows the need for and effect of changing the biasing potential of the detector grid and the change of intensity of incoming signal current. Graph 1 shows the characteristic curve had with a low order of grid bias, showing the shortness of the straight portion. Clearly this adjustment is capable of handling only very weak signals without distortion, as any incoming signal strong enough to change the bias to points approaching the points in the curve will be distorted. Graphs 2, 3, 4, 5 and 6 show how the characteristic curve is increased in straight line content with increase of initial bias, thus bringing out the ability of systems better handling strong signals by increasing the degree of bias. However, it is undesirable to have a permanently fixed high bias, as weak signals are not handled as effectively by high bias conditions as they are by correspondingly low bias conditions.

Having fully described my invention, and not intending any limitations by reason of the choice of the particular systems and arrangements employed herein for explanatory purposes, I claim:

1. An electrical system including a thermionic tube having cathode, anode and one or more interposed grid electrodes, a signal current input circuit connected between a grid electrode and said cathode, an energized output system comprising at least one circuit connected between said anode and said cathode including a resistance in common with said signal current input circuit of such value that it develops by means of the flow therethrough of the unidirectional component of the current of the output system a negative potential on the grid electrode of the said input circuit considerably in excess of the grid biasing potential normal to the operation of said tube, and a resistance in series with the anode to cathode path of a thermionic tube following the first said tube, said resistance constituting a source of potential in said input circuit positively connected to the grid electrode of such value that the resulting difference of potential between the two said sources is substantially that potential required as grid biasing potential for normal operation of said tube.

2. An amplifying system comprising a plurality of vacuum tubes connected in cascade, a resistor connected in the cathode-anode circuit of one of said tubes, a preceding tube, a connection from one terminal of said resistor to the cathode of said preceding tube, an impedance constituting a plate-current biasing impedance for said preceding tube connected in series in said connection, and a connection from an intermediate point on said resistor to the control electrode of said preceding tube.

3. An amplifying circuit comprising a plurality of cascade connected vacuum tubes, a source of direct current, a connection from the positive side of said source to the anode of one of said tubes, a connection from the negative side of said source to the cathode of said tube, a first resistor constituting a plate-current biasing resistor connected in the last mentioned connection, a connection from the negative terminal of said source to the cathode of a preceding amplifying tube, a second resistor constituting a plate-current biasing resistor connected in the last mentioned connection, and a direct current connection from the control electrode of said preceding tube to a point on said first resistor.

4. An amplifying system comprising a plurality of vacuum tubes connected in cascade, a resistor connected in the cathode-anode circuit of one of said tubes, a preceding screen grid tube, a connection from one terminal of said resistor to the cathode of said screen grid tube, an impedance connected in series in said connection, a connection from an intermediate point on said resistor to the control electrode of said screen grid tube, and a connection from an intermediate point on said resistor to the screen grid of said screen grid tube.

5. A circuit arrangement comprising a plurality of cascade-connected vacuum tubes including a screen grid tube, each of said tubes having a self-biasing resistor connected to its cathode and included in its anode to cathode circuit, and a direct conductive connection to the screen grid electrode of the screen grid tube from a point on the resistor which is connected in the anode to cathode circuit of a tube other than said screen grid tube.

6. A circuit arrangement comprising a screen grid tube coupled to a second tube, each of said tubes having a self-biasing resistor connected to its cathode and included in its anode to cathode circuit, and a conductive connection to the screen grid electrode of the screen grid tube from a point on the resistor which is connected in the anode to cathode circuit of the second tube.

'7. A circuit arrangement comprising a screen grid tube coupled to a second tube, a resistor connected to the cathode of the second tube and included in its anode to cathode circuit, a conductive connection from a point on said resistance to the screen grid electrode of the screen grid tube and a second conductive connection from a point on said resistance to the control grid electrode of the screen grid tube.

8. A circuit arrangement comprising a screen grid tube coupled to a second tube, a resistor connected to the cathode of the second tube and included in its anode to cathode circuit, and a conductive connection from a point on said resistance to the screen grid electrode of the screen grid tube, said connection to the screen grid electrode serving as the only source of operating potential for said electrode.

SIDNEY Y. WHITE.

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