US1953455A - Wave transmission system - Google Patents

Description

April 3, 1934. J G, ACEVES 1,953,455

WAVE TRANSMISSION SYSTEM Filed April 6, 1932 INVENTOR BY A? v 4 A'I'I'ORN EYS Patented Apr. 3. 1934 WAVE TRANSMISSION SYSTEM Julius Gourgues Aceves, New York, N. Y., as-

signor to Revelation Patents Holding Company, NewYork, N. Y., a corporation of Delaware Application April 6, 1932, Serial No. 603,467 11 Claims. (01.179-171) This invention relates to electrical transmission systems and with particularity to wave repeating systems employing electron discharge devices.

The invention is in the nature of an improvement on the type of system disclosed in applica-- tion Serial No. 394,172, filed September 21, 1929, and application Serial No. 533,396, filed April 28, 1931.

There are disclosed in said applications systems employing a plurality of sets of triode elements so connected that the grid of the second set may utilize a positive grid swing without producing noticeable distortion in the output. The generic circuit arrangements are such that the grid of the second triode set is inherently positive with respect to its cathode. Under normal conditions of tube design there is, therefore, a considerable flow of steady space current between the cathode and anode of the second triode set.

In order to take full advantage of the improved operating features of the generic system, and at the same time out down the normal plate current of the second triode set, it is suggested in application Serial No. 533,396, to maintain the second grid at or near ground potential by means of a choke coil connected between the said grid and ground. While this latter suggestion achieves a maximum power amplification from the system, with a. minimum of distortion, it nevertheless complicates the circuit connections. Furthermore, as the full advantages of the system require a choke coil which is of minimum ohmic resistance and of high A. C. impedance to the signal frequencies, the cost of such a choke is considerable as compared'with the remaining elements of the system.

Accordingly it is one of the principal objects of this invention to provide a novel method of maintaining the grid of a tube at a predetermined working point on the grid current-plate voltage characteristic.

Another object of the invention is to provide a method of utilizing the output voltages of a triode to maintain the static grid potential.

Another object of the invention is to provide a novel method of utilizing an inductance coupled to the output of a triode for maintaining the grid at a substantially fixed base potential.

A feature of the invention relates to a system employing a pair of triodes in cascade, wherein signal coupling between the triodes is efiected through the intermediary of a coil coupled to the output circuit of the second triode.

Another feature of the invention relates to a system employing a pair of triodes in cascade an anode 6. The grid 5 is directly connected to wherein the grid losses of the second triode are supplied by the cathode-anode of the first triode, and wherein the signal variations are impressed upon the second grid under control of the output of the second triode.

Another feature relates to a wave signaling system employing a pair of tubes in cascade, wherein the first tube supplies the grid losses of the second tube, and wherein the output transformer of the second tube also acts as an input coupling element for said second tube.

A further feature of the invention relates to a system employing a pair of tubes in cascade, in conjunction with an outputtransformer having a secondary winding connected between the grid and cathode of the said second tube.

A still further feature relates to the novel organization and arrangement of elements which go to make up a cheap and emcient power amplifier and/or detector system employing a minimum number of tubes and relatively simple circuit connections.

Other features and advantages not specifically enumerated will be apparent after a consideration of the following detail descriptions and the appended claims.

Referring to the drawing,

Fig. 1 is a schematic diagram of the generic type of system to which the invention is suited;

Fig. 2 is a diagrammatic circuit drawing to explain the operation of the coupling idea of the invention; and

Fig. 3 represents schematically a complete amplifier and/or detector stage embodying principles of the invention. I

Referring more particularly to Fig. 1, there is shown the generic type of system to which the invention is adapted. For a detail description of this system reference may be had to the application Serial No. 533,396. Suifice it for the present to state that the system is intended to utilize two sets of triode elements the first set-comprising an electron emitting cathode 1, a control electrode2, and an anode 3; the second set likewise comprising an electron emitting cathode 4, a grid 5 and the cathode 1, as by means of a wire 7. The signals to be repeated are impressed across the grid 2 and the cathode 1, as indicated schematically by the numeral 8. Connected between the cathode 1 and the negative terminal 9 of the anode potential source (or ground) is a choke coil 10 which is of minimum ohmic-resistance, but has a maximum A. C. impedance at the signal frequencies. It will be noted that the choke 10 is connected in parallel with the space between the cathode 4 and grid 5, consequently the grid 5 is maintained at or near ground potential and the signal variations that are impressed upon the grid 5 merely vary the conductivity of the space between the elements 4 and 6. Inordinary coupling circuits, current flow between the elements 4 and 5 would cause a distortion in the output of the device. However, in the circuit arrangement shown in Fig. 1, this current flow or loss between elements 4 and 5 is compensated for by the current flow between the elements 3 and 1 of the first triode set. In other words, by means of the inductance 10 it is possible to maintain the grid 5 at or near static ground potential, and at the same time the grid 5 may swing positively under control of the signal wave, without producing distortion. One of the important features of this circuit is the fact that the load of the first triode set is between the cathode 1 and the negative terminal 9 of the anode supply (or ground) this load being directly across the grid cathode of the second triode set. Consequently the variations in signaling potential impressed on grid 2 cause corresponding variations between the elements 3 and 1, resulting in similar alternating potential variations being set up across the inductance 10. It is also significant to note that the potential variations on both the grid 2 and the grid 5 are always in phase, whereas in the ordinary coupling circuits these grid potentials are 180 out of phase.

However, the above described circuit requires in addition to the usual output transformer the relatively expensive choke coil 10, and requires additional connections apart from the output transformer. It has been found that the beneficial efiects as regards undistorted power output of the system of Fig. 1 may be achieved without employing an expensive choke coil 10. For the purpose of explaining this feature reference may be had to Fig. 2. However, prior to considering Fig.2, it should be noted that the choke coil 10 of 1 have an ohmic drop that is very small.

Fig. 1 should preferably be such that the impedance between cathode 1 and ground should theothe choke 10 must have a low resistance at zero cycles and high impedance at any audio frequency within the usual range required for faithful tone reproduction. If, therefore, some means can be found for introducing a counter E. M. F. between the grid 5 and the cathode 4, which will have the same eii'ect as the impedance drops in the choke 10, at the same time providing a low I. R. drop for the steady current, a much cheaper and more emcient system can be designed, both as regards power output and faithfulness.

Fig. 2 illustrates schematically one method of achieving this result. In this figure the elements 4, 5 and 6 correspond to the second set of triode elements of Fig. 1. If there is impressed across the elements 4 and 5 of Fig. 2 an electro-motive force of sinusoidal character (either simple harmonic or complex) another corresponding electro-motive force will be set up between the electrode 4 and the electrode 6 through the primary winding 11 of the output transformer. If we assume the transformer 11 to be a perfect or ideal transformer working into a resistance load R, the electro-motive force across the primary winding 11 will be approximately 180 out of phase with respect to the impressed E. M. F. If the output transformer is provided with another or auxiliary winding 12 there will be induced across it an E. M. F. corresponding to the impressed E. M. F., and the phase relation of which will be determined by the polarity of the connections from the winding 12. Preferably this winding 12 has one terminal connected to the cathode 4 (or ground). Consequently the diiference of potential across the points 13, 14 will be the resultant of the impressed signal potential and the induced potential in the winding 12. The voltage across the primary winding 11 is in accordance with the standard formula In the above equation, E equals the voltage developed across the primary winding 11 by the impressed E. M. F. from the source 15 represented by e; 1!. equals the amplification factor of the tube; R is the load resistance; Tp equals the internal impedance of the triode, N11 equals the number of turns in the primary 11, N16 equals the number of turns in the secondary 16. The voltage induced across the winding 12 is given by the following equation;

where the induced voltage is represented by er, and where N12 equals the number of turns in the auxiliary winding 12.

Then by substituting, we find- N11 2 N11 an This shows that when the other factors remain as fixed values, the voltage developed across the auxiliary winding 15 varies proportionately to the impressed E. M. F.

From the foregoing equations, it is possible to calculate the ratio of transformation of the windings of the output transformer. Preferably the system is arranged such that the voltage given by 12 the Equation (3) is equal and opposite to the impressed E. M. F., in consequence of which the difference of potential between points 13 and 14 will always be zero.

Consequently considering the output transformer as an ideal transformer the circuit will function the same whether the points 13 and 14 are disconnected from each other or are short circuited to each other. Under this condition of adjustment therefore we have the functional effect of the choke 10 without the necessity of having a choke of very low ohmic resistance and high A. C. impedance. The winding 12 produces an E. M. F. corresponding to the counter E. M. F. in the choke 10 of Fig. 1, and the magnitude of this E. M. F. may be designed economically merely by the ratio of transformation between the windings 11 and 12. Preferably, the ohmic resistance of the winding 12 should be of the same value as that of the choke 10 of Fig. 1.

The above explanation is of course predicated on the assumption that the output transformer is an ideal transformer. However, by means of suitable resistances this ideal condition may be very closely simulated in actual practice.

Accordingly in Fig. 3 there is shown a complete amplifier system employing the idea disclosed in Fig. 2. In Fig. 3 the signals to be amplified are impressed by means of the input transformer 17 upon the grid 18 of the first triode set. The grid 18 is connected through the condenser 19 to the cathode 20 and the static bias of the said grid 18 may be provided by means of the drop through the resistance 21. The condenser 19 is preferably of suflicient capacity to afford a very low impedance to the impressed signal variations. for example a 2 mfg. condenser maybe employed. The direct current path from the grid 18 to the cathode 20 includes the resistance 22, which is preferably high enough to prevent the cathode being substantially short circuited through condenser 19 to ground. Any suitable so1u-ce of operating potential may be connected across the terminals 23 and 24. While Fig. 3 shows a single source of potential for the anodes and filaments, it will be understood that this is not absolutely necessary, and that the filaments 25 and 26 may be connected in parallel to a separate source of heating current. However, it has been found that the arrangement shown in Fig. 3 enables a very simple and cheap unit to be constructed. In this figure the heater filament 25 for the cathode 20, is connected in series with the filament emitter 26 of the second triode set, and also in series with a resistance 27 for supplying the proper voltage to the filaments in series.

The positive terminal 23 of the supply source is connected to the anode 28 of the first triode set, and also to the anode 29 of the second triode set, through the primary winding 30 of the output transformer. As described in application Serial No. 533,396, the cathode 20 is connected directly by wire 31 to the grid 32 of the second triode 'set. For the purpose of maintaining a preselected normal static grid bias on the electrode 32 there is provided a resistance 33 which is connected in series with the auxiliary secondary winding 34 to the negative terminal 24 of the source of supply (or ground). This resistance 33 not only. serves to give the proper bias to grid 32, but also functions tocontrol the degree of coupling between grid and plate circuits to compensate for the deviance of the said transformer from the 'ideal characteristic. Connected across the auxiliary winding 34 is a resistance 35, preferably adjustable, for equalizing the operation of the transformer at various signal frequencies. The resistance also acts to compensate for the fact that the load B. may not be a pure resistance load. In one actual set up that was found to produce proper results the resistance 35 had a value of from 2000 to 5000 ohms and the ratio of transformation between the windings 30 and 34 was 1.5 to 2. It was found that when the winding 34 was replaced by a choke coil connected similarly to coil 10 (Fig. 1) music was reproduced, but the gain was 5 decibels less than that obtainable with the circuit arrangements of Fig. 3. The resistance 35 also functioned to suppress audio frequency oscillations.

The manner of working of the system of Fig. 3 is in general substantially the same as that described in application Serial No. 533,396. Signals impressed on the grid 18 result in corresponding variations of current between the electrodes 28 and 20. Consequently the potential of the cathode 20 varies in correspondence with the signals impressed on the grid 18. Inasmuch as the cathode 20 is directly connected to the grid 32, this latter grid also will undergo potential variations corresponding to the signals impressed on grid. 18, and futrhermore, the potential variations on the grids 18 and32 will be in substantial phase. The result is that there is impressed across the grid 32 and the cathode 26, signal potentials which produce corresponding changes in the current flow between the said electrodes 26 and 32. There tends to flow between the elements 26 and 32 a steady current similar to the current between the elements 20 and 28, even when no signal waves are being impressed. However, when the winding 34 is connected in circuit as shown. there is induced an E. M. F. corresponding to the signal waves which is 180 out of phase with the waves impressed on the grid 32, so that during the passage of signal variations the grid 32 is maintained at substantially its selected static bias potential. Since, however, the winding 34 is connected across the elements 26 and 32 it produces a counter E. M. F. corresponding to the signal variations, and thus controls the current in the output windings 30 and 36. Functionally, therefore, by the proper connection of the winding 34 there is achieved the effect of the low resistance choke 10 of Fig. 1, without materially affecting the overall gain of the system.

As a matter of fact, with the proper selection of resistance 33 and windings 30 and 34, greater power agnplification is attained with the circuit of Fig. than is attainable with the circuit of Fig. 1, atv the same time reducing the cost of the apparatus. The winding 34 provides the direct current I turn path between grid 32 and cathode 26, similagly to-the choke coil 10 of Fig. 1. However, inst ad of relying on the self-inductance or auto-transformer action of the choke to affect the signal coupling between the tubes, reliance is placed upon the inductive transformer action between windings 30 and 34 to provide the same counter E. M. F. as would be provided by the choke. This is accomplished by choosing the right polarity of connections from the winding 34 to the grid 32 and cathode 26.

It will be understood, of course, that the invention is not limited to an arrangement wherein the winding 34 feeds back voltages equal to the signal waves.

Various modifications may be made without departing from the spirit and scope of the invenion.

Furthermore, while it is preferred to mount the two sets of triode elements of Fig. 3 in the same evacuated container, this is not necessary as the triode elements may be mounted in separate containers and interconnected as disclosed in Fi 1.

Furthermore, while an indirectly heated cathode 20 is shown for the first tube, it will be understood that the invention is. not limited thereto, but that any other well known form of electron emitting cathode may be employed in the first triode set and in the second triode set.

Furthermore, the invention is not limited to a tube having only three elements since it may be applied to tubes having other electrodes in addition to the usual triode electrodes, for example so called shield-grid tubes, pentode tubes, space discharge tubes, etc.

What is claimed is:

1. A wave repeater comprising a first set of triode elements, a second set of triode elements, the load of the first set being directly across the grid and cathode of the second set, said load including an impedance coupled to the output circuit of the second set.

2. A wave repeater comprising a first set of triode elements, a second set of triode elements, the load of the first triode set existing between the cathode and the negative terminal of the anode supply, said load including an inductance coupled to the output circuit of the second triode set.

3. A wave repeater comprising a first triode set, a second triode set, the input impedance of the second triode set being directly across the load of the first triode set, said load including an impedance inductively coupled to the output circuit of the second set.

4. A wave repeater comprising a first triode set, a second triode set, a direct connection between the cathode of the first set and the grid of the second set, an output transformer for the second set, said transformer having a winding connected between the grid and cathode of the second set.

5. A wave repeater comprising a pair of triode sets, circuit arrangements including a short circuit connection from the cathode of the first triode set to the grid of the second triode set and a source of anode potential for causing the grid of the first set to be permanently negative with respect to its cathode, while allowing the grid of the second set to swing positively with respect to its cathode, an input coupling element connected across the grid and cathode of the second set, and means for inducing into said element voltages under control of the output of the said second set.

6. A wave repeater comprising a first triode set, a second triode set, an output transformer for said second set, said transformer having a primary winding, a secondary output winding, and an auxiliary secondary winding on said transformer serving as a direct current return between the grid and cathode of the second set, and also as an input impedance for the said second set.

7. A wave repeater comprising a pair of triode 1,953,455 sets, an output transformer forthe second set,

a winding on said transformer having one terminal conductlvely connected to the cathode of the first set and the grid of the second set, the other end of said winding being conductively connected to the cathode of the second set.

8. A wave repeater comprising a first triode set, a second triode set, an output transformer for said second set, and means including a wind-' ing on said transformer for maintaining the grid of the second set at substantially static ground potential.

9. A wave repeater comprising cathode, grid and plate elements, second cathode, grid and plate elements, the load of the first elements being directly across the second grid and cathode, said load including an impedance coupled to the output circuit of the second elements.

10. A wave repeater of the electron discharge type comprising cathode, grid and plate elements, second cathode, grid and plate elements, an output transformer for said second set of elements, an auxiliary winding on said transformer providing part of the direct current return path for both the grid to cathode of the said second set of elements and the cathode of the sa d first set to the negative terminal of the anode supply.

11. A wave repeater of the electron discharge type comprising cathode, grid and plate elements, second cathode, grid and plate elements, the output load for the first set of elements existing between its cathode and the negative terminal of the anode supply, said load including an impedance coupled to the output circuit of the said second set of elements, and said impedance being also common to the grid-cathode input of the said second set of elements.

JULIUS GOURGUES ACEVES.

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