US1545855A - Amplifier circuits - Google Patents

Description

July 14,, i925. 1,545,855

7 E. o. SCRHVEN AMPLIFIER CIRCUITS Filed July 29, 1924 2 Sheets-Sheet 1 I 3o 94/ 2590 I 5270 no oo 20 00 5600 fie uem lm/emfor: ah 4rd 050W? Jun m W25, 1,545,855

' E. O. SCRIVEN AMPLIFIER CIRCUITS Filed July 29, 1924 2 Sheets-Sheet 2 Patented July 14, 1925.

UNITED STA ES PATENT OFFICE.

EDWARD O. SCRIV'EN, OF NEW YORK, N. Y.. ASSIGNOR TO WESTERN ELECTRIC COM- 'PANY, INQORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

AMPLIFIER omcuirs.

Application filed July 29, 1924. Serial No. 728,880.

T 0 all whom it may concern:

Be it known that I, EDWARD O. SCKIVEN, a citizen of the United States of America, residing at New York city, in the county of New York and State of New York, have invented certain new and useful Improvements in Amplifier Circuits, of whichthe following is a full, clear, concise, and exact description.

This invention relates to electric amplifiers. It has for an object to obtain a constant direct current potential for the control electrode of a repeater or electric discharge device without requiring the use of a special battery for that purpose.

This application is a continuation in art of my application Serial No. 609,985, led

on December 30, 1922.

As is well known in the art, electric discharge devices, when used for example as amplifiers or repeaters, are frequently employed in circuits in which it may be found desirable to maintain a constant direct current potential difference between the control electrode and the cathode, whereby more satisfactory repeating or amplification may be obtaine In accordance with this invention as hereinafter described in detail an impedance element such as a resistance is placed 'in'the space current path of the amplifier between the cathode and the negative terminal of the source of voltage supplying space current to the repeaters, and the control electrode is connected to that terminal of the resistance adjacent to the negative end of the battery. This arrangement makes the control electrode negative with respect to the cathode, which is the arrangement desired in most instances. However, a resistance connected in this way produces coupling between the plate and grid circuits which results in a feed-back of energy through the tube in such a direction as to oppose normal amplification' In order to reduce this coupling for the frequencies to be amplified it will generally be preferable to shunt the alternating current around the resistance by a shunting condenser, for example. Though this arrangement aids in reducing the coupling, there is very likely to'be considerable feed-back, particularl at low frequencies to which a condenser 0 any but a very high capacity offers an appreciable impedance.

This will result in the lower frequenoiesbelng inefficiently transmitte One feature of this invention comprises, the use of a phase reversing network between the common impedance and the grid in order to produce coupling of aiding, polarlty.

Another feature of the invention comprises the use of a tertiary windin-gon the input transformer for introducing a feedback to compensate for the reverse phase coupling of the resistance common to the grid and plate circuits.

In accordance with another feature of this invention the amplification characteristic of the multi-stage amplifier employing a resistance. common to the plate and grid circuits is controlled by means of the coupling afforded by the inter-stage transformers and a condenser or other circuit having an iin vpedance which is variable with frequency in shunt to the resistance. 4

These and other features of the invention can be morev clearly understood by reference to the following description in connection with the drawing which shows diagrammatically several embodiments of the invention: Fig. 1 shows a single stage amplifier employing, in accordance with the invention, a tertiary winding on the input transformer for producing a compensating feed-back. Fig. 2 shows a' single stage amplifier employing a phase reversing network.

Fig. 3 shows a multi-stage amplifier which employs a resistance in the plate battery circuit for obtaining a' negative grid potential in only the last stage.

Fig. 4.- shows a .multi-sta e amplifier in which a negative potential or grids of all the stages is obtained from a common plate battery.

Fig. 5 is a curve showing the amplification frequencycharacteristics of the amplifier of Fig. 3, and

Fig. 6 shows a multi-stage amplifier employingv two tubes in push-pull relation in the last stage, the grids of. which are maintained at anegati-ve potential by means of 'a resistance common to the plate and "grid circuits.

Referring to Fig. 1, the vacuum tube ampli'fier 7 is rovided, as usual, with a filament 8, gri 9, and plate 10. The filament former 6, battery 16, resistance 15 to the cathode 8. The space current of the tube must, therefore, flow through resistance 15 producing a voltage drop therein. The control elect-rode being connected to the most negative end will be more negative than the cathode by an amount equal to the IR drop in the resistance. In order to prevent a variation in the grid potential due to the alternating current also flowing through the resistance; in other words, to reduce the coupling between the plate and grid circuits for the frequencies to be transmitted, a condenser 17 is shunted across the resistance so by the common resistance 15, a

as to bypass the alternating current. However, in most cases the condenser will not eliminate all the coupling between the plate and grid circuits since 1t offers an appreciable impedance to the lower frequencies. A tertiary winding 18 is, therefore, provided on the transformer 13 and connected across the resistance.15 in such a direction that the voltage which is induced in the secondary 14 is in phase with the voltage induced therein by the winding 12. In this way, the opposing coupling produced by the resistance 15 and the condenser 17 is compensated or may even be overcompensated and a boosting efi'ect produced at the low frequencies as is described more in detail in connection with the circuit of Fi 3.

In the arrangement of Fig. 2, 1n order to reverse the phase of the couplin caused high capacity condenser 19 is connected in the circuit between the secondary winding 14 and the negative terminal of batte 16. This condenser is shuntedby a very igh resistance 20 so as to provide a conductive path to keep the grid at a negative potential while offering a prohibitive impedance to alternating currents.

Referring to Fig. 3, the two-stage amplifier comprises the vacuum tubes 21 and 23 coupled together .by an inter-stage transformer 22. The cathodes 24 and 25 are connected in series with a battery 26 which supplies filament heating current. Energy to be amplified is impressed on the circuit through an input transformer 27. One

. terminal of the secondary of transformer 27 is connected to the grid 28 of the vacuum tube 21. The other terminal is connected to the cathode at a point 29 which is directly connected to the negative terminal of the battery 26 so that the grid 28 is maintained at a. negative potential with respect. to the cathode 24 by-the IR drop through cathode 25. A battery 30 is used for supplying the space current to both tubes. The output circuit of the tube 21 may be traced from its plate 31 through the primary 32 of the transformer 22, battery 30 and resistance 33 to cathode 24. The input circuit of tube 22 may be traced from the grid 34 through the secondary 35 of the transformer 22, the resistance 33 to the cathode 25. The

output-circuit maybe tracedfrom the anode 38 through the primary of the output transformer 39 battery 30 resistance 33 to cathode 25. v

The grid 34 is maintained at a negative potential by the IR drop in resistance 33. A condenser 36 is shunted across the resistance 33 so as to provide a by-pass for the alternating current. It may sometimes be desirable to shunt this condenser across both the resistance and the battery, as is indicated in Fig. 4 to be described hereinafter. The current can be traced from the terminal 40 of the resistance 33 to cathode 24, across the space within the vacuum tube to the anode 31, through the primary winding 32, battery 30 (which acts as a conductor for the alternating current) to, the other terminal' il of the resistance 33. Thepotcntial drop in the resistance is, therefore, impressed on the input terminals of the tube 23 through the transformer 22 the primary 32 operating in a similar manner to the tertiary Winding 18 in the circuit shown in Fig. 1. By properly poling this winding it is, therefore, possible to produce an aiding feed back proportional to the drop across the resistance and condenser.

Referring to Fig. 5 in Which'the coordinates represent gain in miles and the abscissae frequency on a logarithmic scale the group of curves A show the amplification of the am lifierin Fig. 3 when the winding 32 is oled so as to produce aidingcoupling and t e group B for opposing coupling;

The curvesof each group represent the amplification with shunting condensers of various capacities as indicated on the curve. Comparison of these curves shows that when the primary 32 is poled to produce opposing couplings, theamplification is low and falls off very rapidly at the lower frequencies,

even if the shunting condenser has a capam a wide ran e of frequencies such as was obby using too low a capacity too great a feed back is obtained which is, likely to result in SlIlglIlQ.

- In the circuit of Fig. 3, when using a 60 volt battery in the plate circuit of the second tube the resistance 32 was adjusted to -3,000 ohms, and shunted by a 0.3 m. f. condenser to give the best results.

The circuit shown in Fig. 4 is similar to that shown in Fig. 3 except that the grid 28 of the first tube is also maintained at a negative potential by the RI drop in resistance 33. This is provided for by an adjustable tap 42. By adjusting this tap any required negative voltage may be supplied to the grid 28. Much more pronounced efiects repeater 51, and in the third stage twocan be obtained with this circuit than with the circuit shown in Fig. 3.

Fig. 6 shows a three-stage amplifier comprising in the first stage a vacuum tube repeater 50, in the second stage a vacuum tube yacuum tube repeaters 52 and 53 connected in push-pull relation. The input circuit of the repeater 50 is coupled to the telephone transmitter 54 by a suitable transformer 56.

The output circuits of the tubes 52 and 53 are coupled to a receiving device 57, such .as a loud speaking telephone receiver bya suitable output transformer 55; The four cathodes 59, 60, 61 and. 62 are supplied with i heating current from a source of voltage 63.

A suitable source of voltage 64 is employed for supplying space current to all the stages.

The grids of the first two tubes, and 51, are maintained at negative potentials by means of resistances 65 and 66 included in the cathode circuits. The resistance 67 is I included in the plate'circuits' of all the tubes resistance 67 adjacent the negative terminal and the control electrodes of the tubes 52 and 53 are connected to the'terminal of the of the battery 64, whereby the'resistance 67 is included in the input-circuits of the tubes 52 and 53. as well [as in their output circuits so that the gridsof these tubes aremaintained at negative potentials with respect .to their cathodes by an amount depending on the IR drop in resis'tance67 in a similar Inannerto that of the amplifiers shown in the other figures. This potential di'fi'erence across theterminals of resistance 67 is in addition to the potential differences produced by the low resistances 7.0 and 71 in the filament heating.circuitsywhereby the control electrodes of tubes 52 and 53 are maintained more negative than the corresponding control electrodes of tubes 59 and 60. This arrangement isparticularly dcsirable since a greater grid cathode voltage is impressed upon tubes 52 and 53 than is impressed upon the preceding tubes. As shown in the drawing, the full potential of battery 64 is impressed between the cathodes and anodes of tubes 50, 51, 52 and 58, exce t for the )otential dro in resist- 1 P l P pling effect of the resistance.

It is to be understood that this invention may possess embodiments widely different from the particular circuit arrangement above described without departing in any way from the spirit of this invention as'defined in the appended claims.

What is claimed is:

1. In an amplifier comprising an electron discharge device having a cathode, a grid and an anode, a source of space current and an impedance common to the anode and grid circuits for maintaining the grid at a fixed potential with respect to the cathode, means for controlling the v anode-grid coupling effect of said impedance, comprising circuit arrangements for impressing upon'the grid an electromotive force opposite m phase to the electromotive force impressed upon the grid by the coupling efl'ect of said impedance.

2. In an amplifier comprising an electron discharge device having a cathode, agrid and an anode, a source of direct current potential associated with the anode circuit. and a resistance common to the anode and grid circuits for. maintaining the grid at a negative potential with respect to the cathode, a circuit having an impedance variable with frequency shunting said resistance, and means for controlling the amplification of low frequencies comprising circuit arrangements forimpressing on the grid an alternating electromotive force opposite in phase to that which is impressed by the natural coupling effect of said resistance .and said shunting circuit. j

3. In'an amplifier comprising an electron discharge device having a cathode, a grid and an anode, a source of potential associated with the anode-cathode circuit, and a resistance common to the grid and anode circuits for maintaining the grid at a negative potential with respect to the cathode, means for controlling the frequency-amplification characteristic of the amplifier comprising a circuit having an impedance variable with frequency connected in shunt to said resistance and transformer means -for impressing on the grid an electromotive force opposite in phase and proportional to the electromotive force impressed thereon by the natural coupling effect of said resistance and shunt circuit.

5. In a multi-stage amplifier, a plurality of electron discharge devices each having a cathode, a grid and an anode, a common source of space current for said devices, an impedance common to the grid and anode circuits of one of said devices for maintaining the grid of said device at a negative potential with respect to the cathode, and transformer means for impressing upon the grid an electromotive force opposite in phase to that which is impressed by the coupling effect of said impedance.

6. In a multi-stage amplifier, an electron discharge device having a cathode, a grid and an anode in each stage, a common source of anode-cathode potential for a plurality of stages, an impedance connected between the negative terminal of said source of potential and the cathode of at least one of the stages, connections from the terminal of said impedance adjacent to the negative terminal of said source of potential to the grid of one stage, connections from said impedance to the anode-cathode circuit of the preceding stage and a transformer for connecting said two stages having such a polar ity that the secondary termlnal connected to the grid of said first mentioned stage is of apposite polarity to the primary terminal connected to the anode of said preceding stage.

7. A multi-stage set comprising an electric discharge device in each stage having an anode, a cathode, and a control electrode, a common source of voltage connected to the anode and cathode of a plurality of stages for supplying space current to said devices, an impedance traversed bycurrent from said source, a connection between'the control electrode of one device and the cathode of said one device, said connection including at least a portion'of said impedance, and means for preventing said control electrode connection from causing said set to sin.

8. A multi-stage set comprising an e ectric discharge device in each stage having an anode, a cathode, and a control electrode, a common source of voltage connected to the anode and cathode of a plurality of stages for supplying space current to said devices, an impedance traversed by current from said source, a connection between the control electrode of one device and the cathode of said one device, said connection including at least a portion of said impedance, and means for by-passing alternating currents around said impedance.

'9. A multi-stage set comprising an electric discharge device in each stage having an anode, a cathode, and a control electrode, a common source of voltage connected to the anode and cathode of a plurality of stages for supplying space current to said devices, a resistance traversed by current from said source, a connection between the,

controlfelectrode of one device and the cathode of said one device, said connection including at least a portion of said resistance and a condenser of large capacity connected effectively in shunt to said resistance...

10. A multi-stage repeater set comprising a vacuum tube amplifier in each stage having an anode, a cathode and a control elec-- trode, a common source of voltage connected to the anode and the cathode of a plurality of the stages for supplying space current to said devices, a resistance connected .between said cathodes and the negative terminal of said source and arranged to be traversed by the space current from said source, a. connection between the control electrode of a device in a stage of said set subsequent to the first and the cathode of the said one amplifier, said connection including said resistance,'and a condenser of.

large capacity connected effectively in shunt to said resistance.

11. A multi-stage set comprising an electric discharge device in each stage having an'anode, a cathode, and a control electrode, a common source of voltage connected to the anode and cathode of a plurality of stages for supplying space current to said devices, an impedance traversed by current from said source, a connection between the control electrode of one device and the cathode of said one device, said connection including at least a portion of saidimpedance, and means lowerlng the impedance across said portion for preventing said control electrode connection from causing said set to sing. I

In witness whereof, I hereunto subscribe my name this 25th day of July A. D., 1924.

- EDWARD O. SCRIVEN.

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