US2127334A - Electronically coupled regenerative amplifiers - Google Patents

Description

A g.16,1938. J. L. HATHAWAY 2,127 3 ELECTRONICALLY COUPLED REGE NERATIVE AMPLIFIERS Filed Dec. 16, 1932 4 Sheets-Sheet l INVENTOR- i u. L. HATHAWAY ATTORNEY- J. IL. HATHAWAY 2,11%334 ELECTRONICALLY COUPLED REGENERATIVE AMPLIFIERS Filed Dec. 16, 1932 4 Sheets-Sheet 2 ATTORN EY- Aug. 16, I938. J; L. HATHAWAY ELECTRONICALLY COUPLED REGENERATIVE AMPLIFIERS Filed Dec. 16, 1932 RM n 2 mw N NM m ET I W: N 2 nm fi L J I I I 1 I I 1 1 I l I I I l I l I I I 1 I I I l I I I I I I I 1 I 1 I I I I 1 11-11::|||||1|||1||1LY|||||||J 1 u u n Y m m n m u m m m M\ m m m a u h h u 1 w n u I Jo h a Q a n n m: Q) Q n m m m H m m M N b G) X w m 2 NU N v n MN u k n S w\ n U n m Q Q m n u b x m i. m m m m m "I |L I |L N J. L. HATHAWAY 2,127,334 ELECTRONICALLY COUPLED. REGENERATIVE AMPLIFIERS Filed Dec. 16, 1932 4 Sheets-Sheet 4 I l l I I I l 1 v INVENTOR- J.L.HATHAWAY ATTORNEY- Patented Aug. 16, 1938 UNl'iED STATES PATENT OFFICE Jarrett Lewis Hathaway, New York, N. 1., assignor to Radio Corporation of America, a corporation of Delaware Application December 16, 1932, Serial No. 647,626

Claims.

This invention relates to a method of and device for relaying and amplifying alternating currents.

More in detail, this invention relates to the amplification of alternating current and/or volt ages or potentials by the use of a thermionic tube amplifier arranged in a novel circuit and utilizing a novel system of controlled regeneration.

The thermionic tube may be of a type having four or more electrodes. The regeneration as ob tained in the present invention is obtained by coupling between the cathode circuit and the control grid circuit. The present arrangement is novel in that the control grid circuit is not cou pied to the output circuit yet controlled regeneration, to the extent necessary to obtain increased amplification, is provided for. The object in keeping the input and output circuits uncoupled will appear more in detail hereinafter. The anode or output element is coupled only by electronic means to the input elements and circuit and to the regenerative parts of the amplifier. Thus, the output circuit and its load are not appreciably affected by the regeneration, nor do they affect the regeneration.

Regeneration generally occurs in thermionic tube amplifiers known in the prior art unless some special means is taken to prevent such regeneration. It is a well known and accepted principle that regeneration without self-oscillation may increase the amplification of a thermionic tube enormously by decreasing the effective resistance of the associated circuits and by lessening the damping effect of said tube and said circuits on the signal currents. However, heretofore such regenerative amplifiers have had certain inherent defects which in general rendered them. unsatisfactory. Especially do these defects become noticeable when several amplifier stages are connected in cascade. In such an arrangement interaction occurs not only between input output circuits of a stage but also between the stages and a final amplifier may interact or react on preceding amplifiers due to the regenera tion or feed-back effect between the grid circuits and the output circuits, or between one output circuit and a preceding input circuit, or vice ve all of which may be and often is caused by inductive or capacitive transfer of energy from one circuit to another, either by way of induction, capacitive coupling, or via the tube impedance. This feed-back effect, or regeneration, makes such amplifiers unstable and subject to self-oscillation. When in cascaded amplifiers, the feed-back is from a given stage to a preceding stage or stages, causing regeneration, the degree of useful regeneration is limited, due to selfosciilation occurring before much amplification gain has been attained. The amplification gain is much greater if each stage is separately regenerative, and is relatively unaifected by input and output tubes and loads.

Moreover, with the amplifiers of the prior art it has been difficult to cover a wide band of frequencies without readjusting the permissible 10 feed-back between circuits of a stage or between stages. Furthermore, where provision has been made for readjusting the feed-back circuits or elements thereof, the operation thereof is difiicult and usually not satisfactory.

The primary object of the present invention is to provide a method of and means for relaying and/or amplifying alternating currents and/or voltages whereby extraordinary amplification may be obtained.

Another object of the present invention is to provide a method of and means for amplifying and/ or relaying alternating currents and/ or voltages whereby extraordinary amplification may be obtained through the use of stable and easily controlled regeneration.

A further object of the present invention is to provide a method of and means for amplifying and/or relaying alternating current voltages, increasing extraordinarily the amplitude of said voltages during the relaying process, to obtain such amplification by the use of easily controlled regeneration, and to provide means whereby, in spite of said regeneration effect, several stages may be connected in cascade and operate inde- 3 pendent of each other as far as reactions therebetween due to couplings are concerned.

An additional object of the present invention is to provide a method of and means for amplify-- ing alternating currents as described above in which the method of and means for obtaining regeneration is of a novel nature and such that the method of and means for amplifying will operate efiiciently over an extremely wide frequency range without change or adjustment of the regeneration circuits.

The novel features of the present invention have been pointed out with particularity in the claims appended hereto.

The novel method of amplifying and/or relaying oscillations, and the manner in which the same may be carried out will be best understood from the following detailed description thereof and therefrom when read in connection with the drawings in which like reference characters indicate like parts, and in which:

Figure 1 illustrates a single stage electronic coupled regenerative amplifier as of the present invention;

Figures 2, 3 and 4 show modifications of the arrangement of Figure 1; while Figures 5, 6, 7 and 8 show modified details of the prior arrangements.

Referring to the drawings, and in particular to Figure 1 thereof, V indicates a thermionic tube of the screen grid type having its cathode I indirectly heated by a filament 2. An input inductance L1 is connected between the control grid 3 and the negative terminal of the anode and screen grid voltage source 8 and may be tuned to the signal frequency by a capacity C1 connected, as shown, in parallel therewith. Oscillations to be amplified or relayed may be impressed from any source not shown onto the inductance L1 by way of an inductance 4 coupled thereto. The input circuit connected by way of L1 between the control electrode 3 and the cathode I is completed, as shown, by way of a resistance R2 shunted by a capacity C2 in series with an inductance L2. This inductance L2 is also in the cathode return circuit. The inductance L2 is inductively coupled to inductance L1 and serves as a feedback coil to provide the regeneration effect.

In order to control the regeneration effect a variable resistance R1 is connected in shunt with inductance L2, as shown. The resistance R2 is a biasing resistance to determine the potential difference between the cathode l and the control electrode 3, while the condenser C2 by-passes radio frequency oscillations around this resistance.

The anode 6 is connected, as shown, to an output inductance L3. The anode direct current circuit is completed by way of battery 8, resistance R2, and inductance L2 and resistance R1 to the cathode l. The screen grid electrode I 0 is connected, as shown, to a point on the source 8. Radio frequency oscillations in the anode circuit and in the screen grid electrode circuit are bypassed around the source 8 by by-pass condensers C4 and C3 connected as shown. The output inductance L3 is shielded from the tube V and from the input inductances L1 and 4 and the inductance L2 in the cathode circuit by a shield S.

The oscillations amplified in the tube V and appearing in L2 may be utilized in any work circuit connected with the inductance ll coupled to L3.

In operation the screen grid tube V amplifies and relays the alternating current voltages appearing on its control grid 3 in the usual manner. The amplified and relayed voltage oscillations appear in the output inductance L3. The cathode inductance L2 carries the total of the screen grid, control grid and anode currents, both the spacing currents, that is, the direct currents, and the alternating currents. These currents are pulsating in characteristic and have a frequency which is determined by the frequency at which the control grid 3 is excited. This pulsating voltage or current energy is transferred inductively, in this case, from the inductance L2 to the input circuit of V by way of inductances L1 and/or 4. The phase of the energy fed back into the input circuit is such as to augment the energy therein and to produce self-oscillation within the amplifier. However, in practice, the feed-back voltage is kept below a point of oscillation by the shunting effect of the regeneration control R1,. The

result is that the grid electrode 3 receives excitation far above that due to the original applied voltages, yet excitation of the control grid is controlled in frequency and in amplitude by the original signal.

The regeneration effect obtained in the amplifier, as described thus far, is substantially independent of the anode and output circuit. The anode and output circuits are electrically isolated from the input electrodes, and the input circuit and the regenerative elements of the amplifier and should receive energy only by the electronic stream. The isolation of the anode is accomplished by the screen grid electrode H], which is maintained at a positive potential by the source 8. The by-pass condenser C3 acts as a filter in this case and assists in maintaining a potential on the screen grid electrode which is constant at all times. With the screen grid elements maintained at constant potential and with a high output circuit impedance, the anode space current may have greater magnitude than the screen grid current, although the magnitude of the screen grid current pulsations, due to grid excitation, will be greater than the plate current pulsations. If the anode circuit impedance is high and the screen grid circuit impedance is low this may not be entirely true. This pulsating screen grid current constitutes one of the components in the cathode circuit and is the major source of regeneration. The anode current pulsations likewise flow in the cathode coil but have a minor effect on regeneration. The output inductance L2 is magnetically and electrostatically isolated with respect to V, and with all elements to the left of V, by the shield S. In this amplifier, therefore, the only coupling between the input electrode and input circuits and the anode and output circuits is by way of the electronic stream flowing from the cathode I through the grid electrodes 3 and Hi to the anode 6.

While, for purposes of illustration, I have shown direct current sources as being utilized to energize the electrodes in this amplifier, it will be understood that any type of potential sources now in common use may be used, whether they be direct or alternating current.

Where a greater amount of amplification is desired than can be obtained by the single stage shown in Figure 1, the arrangement of Figure 2 may be used.

In the arrangement of Figure 2 applicant has shown three stages connected in cascade. Each of these stages is substantially similar to the single stage of Figure l and a detailed description thereof at this point is deemed unnecessary. It is, however, noted that the reference numerals and characters of Figure 1 are used to indicate the corresponding or similar parts in Figure 2.

In the arrangement of Figure 2 the oscillations to be amplified are applied to inductance 4 and the output oscillations are impressed from the final anode inductance L3 on to the inductance H.

Due to the tendency of the several stages in cascade to oscillate because of coupling between the stages and elements thereof, it is desirable to place in each screen grid lead and in each anode lead a radio frequency choke coil RFC between said elements and their power sources, not shown, and to connect the telimnal u; ea... or WM cadjacent the electrode to which it is connecte to the shield S and to round bv by-pass cnn. denser C3 and C4 as shown, thereby completely filtering all oscillations from the energizing source and preventing reaction between said oscillations in said sources. The negative terminal of the anode and screen grid source is also grounded to the shields.

Where several stages are connected in cascade, as in Figure 2, the shielding S between stages must be complete. Shielding in this case is accomplished by enclosing each regenerative input circuit and the amplifier tube which it feeds in a separate metallic shield S of any one of the well known types of good shields. The output circuit L3", ii of the final stage is also enclosed, as shown, in a separate individual shield to prevent reaction of this circuit which carries a larger amount of energy than on the prior stages or circuits. Here, as in Figure 1, further shielding is provided between input and output electrodes by the screen grid electrodes H3, H3 and The operation of the arrangement of Figure 2 is similar to the operation of the arrangement of Figure 1, except that the oscillations are amplified repeatedly in the several stages and an enormous amount of amplification can be obtained. In each amplifier the only coupling between the anode and output circuits and the input circuits and the control grid is electronically by Way of the electron stream between the cathode and anode. Here, as in the prior arrangement, regeneration is controlled in each stage by the resistances R1.

When it is desired to amplify ultra high .frequency energy the push-pull arrangement disclosed in Figure 3 may be advantageous. In this arrangement the incoming oscillations are impressed from inductance 4 on to the symmetrical inductances L1 connected between the control grids 3 of vacuum tubes V. The oscillations are amplified and repeated in tubes V and appear on the anodes t and in the anode circuit of tubes V including the inductances L3 connecting the anodes 63 to the direct current source, not shown, by way of lead !2. The amplified oscillations are impressed from the inductances L3 to the symmetrical inductances L1 connected with the control grids 3 of vacuum tubes V1, amplified therein, and appear in the output inductances L3, from which they are impressed on to the inductance H, which may be connected with any load circuit. In this arrangement the input circuits connected to each of the pairs of cascade amplifiers V, V, V1 and V1 are tuned by variable capacities C1 and C1.

In this arrangement the desired potential difierence between the cathodes and the control electrodes is obtained, as in the prior arrangements, by the use of resistances R2 and parallel capacities C2. These resistances and capacities may be placed on the grid circuit adjacent the cathode, as in stage V, or adjacent the grid, as in stage V1. In the latter arrangement the biasing resistance value is considerably higher than when used in the cathode circuit, since the grid current is only a fraction of the cathode current.

Here, however, the control of the transfer of energy between the cathode circuit and the input circuits to produce regeneration is effected in a manner different than in the prior arrangements. Regeneration control is obtained in this pushpull arrangement by connecting the leads M between the cathodes of the push-pull tubes to movable points on the inductances L1 and L1. By sliding these points along the aforesaid inductances, the desired amount of regeneration or coupling between the cathode circuit and the grid circuit may be obtained.

In order to insure symmetry of the input circuits as to their several portions and electrical balance of said circuits and all portions thereof with respect to the grounded shield S, the electrical centers of inductances L1 and L1 are connected to the grounded shield by leads it, which also serves as the high voltage connection. This symmetry of the circuits is further enhanced by the manner in which anode potential is supplied to the anodes by way of the windings L3 and L2 by Way of leads i'l connecting the electrical center of these windings to a source of positive potential, not shown, which has its negative terminal connected to the shield S.

The operation of the arrangement of Figure 3 is the same as the operation of the arrangement of Figure 1 except that a push-pull action is obtained in the present case. Furthermore, in the present case the several stages are shielded so that electron coupling only is obtained by the input and output circuits and no coupling is obtained between elements of the adjacent stages. In the present arrangement the circuits and tubes are symmetrically grounded with respect to the shield so that the entire amplifier is balanced as to its components and with respect to ground contributing toward stability in operation.

In Figure 4 is shown an amplifier comprising a stage having a single tube V feeding into a push-pull stage including thermionic tubes V1. This push-pull stage in turn feeds into a second push-pull stage including the thermionic tubes V2. This arrangement is in some respects similar to the arrangement described in detail hereinbefore. In this arrangement regeneration is obtained in the first stage by connecting the cathode l of tube V to a sliding point on the inductance L1. In the second stage, that is, the first push-pull stage, regeneration is obtained by connecting the cathodes I by leads M to sliding points on the inductances L1 so that the amount of inductance in the cathode circuits and the grid circuits may be varied to cause the desired regenerative coupling between these circuits to produce the amount of regeneration desired. The filaments 2, 2 of tubes V and V1 may be heated from the same source by leads H9. The tubes V2 are supplied with cathode heating current from any source by way of separate leads W, as shown. One of the leads i6, preferably the lead connected with the negative terminal of the cathode heating source, is connected as shown, to the grounded shield S.

In the final push-pull stage V2 of Figure 4 the inductances L1 may be of heavy copper wire. Portions of these inductances L1" may serve as. portions of one of the filament heating leads. The other filament heating lead may be wound side by side with the turns of the inductances L1" but insulated therefrom. The inductances L1 may comp-rise a conductor in the form of a heavy tube, preferably of copper as shown in Figure 5. Then lead may be within the tube. This, as in the case where heavy copper wire is used, is to prevent heating in this grid circuit by lowering the resistance of said circuit to high frequency oscillations.

The tubes V2 have in the present case directly heated filaments. The filaments may be heated by circuits which include as one lead a portion of the copper tubing of the inductances L1". This has been shown more in detail in Figure 5, in which a portion of the copper tubing of inductances L1 forms one lead of the filament heating circuit, for example, the negative lead (since the -A usually is grounded). The other lead to the filament of the tubes may be a conductor threaded within the hollow conductor, as shown. The portion of the hollow tube conductor of inductances in the cathode lead and the conductor threaded within said hollow conductor serve as inductances in said filament lead to prevent radio frequency oscillations from reaching the filament heating source by way of leads l8.

Here, as in the prior case, the desired degree of regeneration is obtained by adjusting the leads [4 and I 4 to the desired point on the grid inductances and symmetry and balance is obtained by grounding the electrical centers of the grid inductances of the push-pull stages to the shield S, and by supplying anode potential by leads connected to the electrical centers of the anode windings.

In the present arrangement, due to the fact that different type tubes are used, two sources of filament heating current may be used, one of the sources furnishing current to the filament of tubes V, V1, and the other source furnishing current to the directly heated filaments of tubes V2.

The operation of the arrangement of Figure 4 is substantially similar to the operation of the arrangement of the prior figures and a detailed description thereof is thought unnecessary at this point. Here, as in the prior arrangement, amplification in each stage is obtained by means of electronic coupling only, and each stage is shielded by the shield S from the prior stages so that the anode circuit of each tube is coupled only electronically to the input electrodes and input circuits. For this reason an enormous amount of amplification can be obtained without the amplifier oscillating.

In some cases it may be desirable to replace the filament heating circuits and the input inductances of Figure 5 by the arrangement shown in Figure 6.

Especially is the arrangement of Figure 6 desirable when for some reason it is thought unwise to have the grid inductance, that is, the hollow tubular inductance in the grid circuit, carry the heating current. In this case the filaments of the tubes may be heated by leads threaded within the inductances L and insulated therefrom as shown. In this modification the resistance R2 and capacity C2 may be omitted, and grid bias may be supplied from a source as shown by connecting the electrical center of the inductances L to the negative terminal of said source and the positive terminal of said source to ground to the shield S and to the negative terminal of the filament, anode and screen grid sources.

Other methods of supplying filament heating voltage to direct heated tubes may be used, such as radio frequency choking inductances I as shown in Figure 8 in each filament supply lead or one choking inductance I in one lead with the other supply connection through the grid inductance as shown in Figure 7. In these figures the inductances L may be as in any of the prior figures.

Having thus decribed my invention and the operation thereof, what I claim is:

1. An electron relay system comprising, a container enclosing an electron emission element, a control electrode and an anode, an input circuit between said control electrode and said emission element, an output circuit between said anode and said emission element, said circuits being shielded from each other, an auxiliary electrode in said container maintained at a positive potential relative to said emission element and a circuit connected between the auxiliary electrode and said emission element, said circuit having a portion in common with a portion of said input circuit and means coupling said portion common to said circuits to the remainder of said input circuit to produce controlled regeneration.

2. An electron relay system comprising, a thermionic tube having a control grid electrode, an emission element, and an anode electrode, an input circuit connected between said control grid electrode and said emission element, an output circuit connected between said anode and said emission element, said input circuit having a portion variably coupled to the remainder of said input circuit, means for shielding said control electrode from said output electrode comprising an auxiliary electrode interposed between said electrodes and maintained at a positive potential relative to the emission element, means for producing controlled regeneration in said input circuit, including a circuit between said auxiliary electrode and said emission element, said lastnamed circuit including said portion of said input circuit, and shielding means interposed between said output circuit and said input circuit.

3. An electron relay of the regenerative type comprising, a thermionic tube having a control grid and an anode electrode, and an emission ele ment, an input circuit connected between said control grid and emission element, a circuit connected with said emission electrode and regeneratively coupled to said input circuit, regeneration control means in said last named circuit, an output circuit connected between said anode and emission element, means within said thermionic tube for shielding said anode electrode from said control grid, and means without said thermionic tube for shielding said input circuit from said output circuit.

4. An electronically coupled regenerative amplifier comprising, a thermionic tube having input and output electrodes and an emission element, a circuit connected between the input electrode and emission element, an output circuit connected between the output electrode and emission element, said circuits having a portion in common, said portion including an inductance in series with a resistance shunted by a capacity, and a variable resistance connected in parallel with said inductance, said inductance being coupled to said input circuit.

5. A cascade push-pull amplifier comprising a plurality of stages of thermionic tubes, each stage comprising a pair of tubes in push-pull relation having regenerative input circuits and output circuits which are coupled to said input circuits primarily by the electron stream in said tubes, said input circuits and said output circuits being magnetically and electrostatically shielded from each other.

6. An electron relay comprising, a thermionic tube having an output electrode, an input electrode, and an emission element, an input circuit including said emission element, said input circuit having portions coupled together, an output circuit coupled to said tube, said output circuit including a portion of said input circuit, means Within said tube for shielding said input electrode from said output electrode, and means for shielding said input circuit from said output circuit.

7. An electron relay system comprising a thermionic tube having a control grid electrode, an emission element, and an anode electrode, an input circuit connected between said control electrode and said emission element, means in said input circuit for producing regeneration in said circuit, an output circuit connected between said anode and said emission element, said output circuit being coupled mainly to said input circuit by way of the electron stream in said tube, means for shielding said control electrode from said output electrode comprising an auxiliary electrode interposed between said electrodes and connected by way of a potential source to said emission element, and shielding means interposed between said output circuit and said input circuit.

8. A cascade pushpull amplifier comprising a plurality of stages of thermionic tubes, each stage comprising a pair of tubes in pushpull relation having regenerative input circuits which are electrostatically and electromagnetically balanced with respect to each other and to ground, and balanced output circuits which are coupled to said input circuits mainly by way of the electron streams in said tubes, said input and output circuits being magnetically shielded from each other.

9. A11 electronically coupled regenerative amplifier comprising, a thermionic tube having an input electrode and an output electrode and an emission element, an output circuit including a variable impedance connected between said output electrode and said emission element, an input circuit including said variable impedance connected between said input electrode and said emission element, said circuits having a portion including said variable impedance in common, and means for coupling said common portion to the remainder of said input circuit.

10. An electronically coupled regenerative amplifier comprising, a thermionic tube having an anode, a cathode, a control grid and an auxiliary electrode, an input circuit connected between said control grid and said cathode, an output circuit connected between said anode and said cathode, an auxiliary circuit connected between said auxiliary electrode and said cathode, all of said circuits having a portion in common through which the current between said electrodes flows, and means for producing controlled regeneration in said circuits including a Variable impedance in said common portion, and means for coupling said common portion to said input circuit.

J. LEWIS HATHAWAY.

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