US1851549A - Method and apparatus for power amplification - Google Patents

Description

March 29, 1932. M. E. THOMPSON 9 METHOD AND APPARATUS 'FOR POWER AMI LIFICATION Filed June 4, 1927 E L M Patented Mar. 29, 1932 PATENT OF-RICE" mom a. rnourson, or runaway, msnvam mmion AND nrmarus non rowan. mmicarroir Application m a June 4,1927. Serial I'm 198,4 9.

My invention is concerned with a new method of using thermionic currents in pow- Y en amplification and with novel apparatus adapted for use in practicing the method.

6' When a magnetic field is impressed at" right angles to th path of an electron stream,

the electrons ar deflected in a direction perpendicular both to the direction of the m%:

net field and to the electric field causing .t e

electron flow, the ma itudeand direction of the deflection depen ing upon the strength and relative direction respectively of the two fields.

- My invention comprises a method for utilizing, and apparatus for applyin ,thls

phenomenon in power amplification o a1ternating or otherwise var ing currents. I

cause thecurrent that is to team lified to create an electromagnetic field at right angles to 2 the flow of electrons from a heated cathode o a plurality ofpositively charged anodes. I

place a shield or shields between the electrodes in such a way as to intercept a part of the electron flow to the various anodes and preferabl insuch a way as to insure that each ano e receives substantially equal current from the heated cathode when the magnetic field strength is zero. The deflection of the electronic currentoccurring when the 80 magnetic field is not zero is made to cause a change in the distribution of the electronic current to the various anodes without changing substantially the total current received b all of the anodes. In this manner an clianges in the direction of strengthof the controlling current, that is in the current which creates the magnetic field and therefore determines its strength and direction,

are reflected in changes in the currents in the various anode circuits. a

a The modern practice as exemplified in the use of the well-known three-electrode vacuum tube varies the strength of the current to the-anode in response to changes in an electrostatic field applied to the grid. As outlined above my ethod comprises the maintenance ofa subs antiallyconstant current with its distribution varied in response.

to changes inlan electromagnetic field. This "radical departure from the modern practice results in the elimination of some of the in-, herent-disadvantages of the three-electrode tube and also results in' certain economies in operation all of which will become apparent from the following description of the appal5 ratus and its operation.

For a better understandin of my invention reference should be ha to the accompanying drawings of which Figs 1a, 1b. and

1c illustrate diagrammatically the fundamental principles of my invention. Fig. 2

is a cross-sectional view of the preferred form of a vacuum tube constructed to operate according to my invention, and- Fig. 3 illustrates diagrammatically one application,

of my amplifying device.-

In Eigs. 1a, 1b and 1c, 1 is a coil adapted to carr alternating current; 2 is a filament heated y a battery 3 to which it is connected b leads 4; 5 and 6 are shields of any" suita le"mate rial and 7 and 8 are metal inclosed within an evacuated chamber. It is immaterial whether or not the coil 1 is within this chamber. If no current is'flowing in so coil 1 then the distribution of the electrons from the filament to the plates and shields will be as shown by the broken lines 28 in Fig. 1a.- There will of course be electrons emitted radially in 'all directions from the filament but only that part of the stream indicated is material to this descri tion. The plates, being symmetrically locate with respect to the shields and ament and being at equal otentials with res ect to the filament WiIi each receive equa electronic current. If new a current is sent through the coil 1 in an anti-clockwise direction, a magnetic field at right angles to the paper and with its positive direction upward from the Eaper will be impressed within the coil. eld will deflect the electronic current to the left so that the plate 8 will receive current over a larger area, and the plate 7 over a smaller area, than when no current is flowlng in the coil 15 thetotal current to both of the plates being substantially the same in either case. With increasing anti-clockwise current in the coil 1, the current to plate v7 5 and through impedance 9' decreases and the current to plate 8 and through impedance 1O correspondingly increases. A ma et1c field strength sufiicient to deflect all the avallable electronic current to plate 8 is shown in 10 in icated by 29. Fig. 1a illustrates similarly the extreme case when all of the available electronic current is received by plate 7 under a field impressed by current flowing in a clockwise direction in coil 1. With a ternatin or pulsating current through coil 1 the e ectronic current will therefore be deflected synchronously with the current in the coil first to one late and then to the other; the current to p ate 7 decreasing while that to plate 8 is increasing and vice versa.

To utilize the general principles illustrated in Figs. 1a, 1b and 10 an arran ement such as shown in Fig. 2 is preferre An evacuated glass tube or bulb, shown in crosssection at 12 is surrounded by the coil 1. The filament 2, within the tube and along the axis of the coil, is heated by current led to the filament b wires 4 from the battery 3. The lead wires rom'the battery to the filament would be in practice of course introduced into the tube at one end in the usual manner.

The filam'erit 3 is surrounded by a cylindrical shield within the tube and having a comparatively small diameter. The shield is provided with longitudinal slots 13 of uniform width which, in the embodimentillus- .trated, arefour' in number and of approxi- 9 mately equal circumferential width with the section of the shield between the slots. The

anodes are'formed of separated segments 7 and 8 of a second cylinder coaxial with the shield and of a substantially greater diam- 45 eter; the number of segments being twice that of the slots 13. The spacing of the segments issuch that the arc subtendedv by any slot 13 or section of the shield 5' subtends approximately one-half of each of two neigh- 50 borin anodes 7 and 8. The'anodes 7 are in electrical contact through wires 14 and the anodes 8 are in electrical contact through wire 15. The anodes 7 and 8 are connected through equal impedances 9 and 10 res c- 55 tively with the positive terminal of the attery 11 which in turn is connected at its negative terminal with the battery 3. The particular method of supporting the anodes,

shield andfilament within the tube, or in 60 making the electrical connections is immaterial to my invention and may be done in any well-knownmanner. -The axial length of the anodes and shield are preferably equal to or greater than that of the filament and 05 substantially less than thatof the coil 1.

Fi 1b; the deflected electron stream being eanne The operhtion of the apparatus of Fig. 2 is similar in all respect wit that already described in connection with Fi s. 1a, 1b and 10 the only difference being t at the cylindrical arrangement permits a reater pro- 7 portion of the electrons given oi? by the filament to contribute to the total current. The distribution of this electronic current when no current is flowing in the coil 1 is shown by the broken lines 28 radiatin from the filament; the curved lines 29 in icating the path of the electrons when deflected entirely to plates 8 by a clockwise current in coil 1 of maximum strength for the design of the particular tube. For simplicity that art of the stream of electrons intercepted y the shield. 5 is not illustrated. I

In the. operation of such a tube as that illustrated in Fig. 2 it is highly desirable that the filament temperature be, maintained low enough to insure that the lowest potential applied to the plates will be sufiicient to draw to the plates all of the electron current passing through the slots 13. If the filament temperature is thus restricted substantially constant total plate current is obtained and variations in the current in coil 1 are proportionately reflected in variations in the currents through impedances 9 and 10. In practice, the impedances 9 and 10 will form the primary of a transformer, the secondary being so connected that decreasing current in impedance 9 will affect the secondary voltage in the same direction as increasing current in impedance 10.

The use of a lower filament temperature than that usually employed in the three-electrode tubes results in a substantial increase in the life of the tube and in additional economy in the size of the battery 3, that is in the so-called A battery necessary to supply the filament current. iDue'to the fact that a tube operated according to my invention passes a constant plate current, the internal resistance of the tube is constant and the errors due .to changing tube resistance usually occurring in the modern tubes are eliminated. Furthermore, the internal capacity eflects which now comprise perhaps the most serious drawback of the three electrode tubes are eliminated by a tube such as that in Fig. 2 as in operation the capacity between the two sets of plates and the other elements of the tube will always balance each other due to the fact that the potentials at the two sets of plates rise and fall oppositely. The shields 5 may be grounded or given a slight positive-0r negative potential as desired and as is found preferable for the particular tube and for the particular use to which the tube is put.

In Fig. 3 I have shown diagrammatically two amplifying stages of a radio circuit employing a tube such as that of Fig. 2. For convenience the tube is shown symbolically u cuit controls the filament temperatures.

' terminal of the B assume ary of transformer18 due to the reception filament 2 and a coil 1. The shield is notillustrated and the various elements are now shown in their relative positions. The A battery, 3, supplies current in parallel to the filaments 2. As in the other figures, the plates 7 and 8 are connected through impedances 9 and 10 respectively to the positive battery 11, the negative terminal of which is connected to the positive terminal of the A battery. An adjustable resistance 16 in the A battery antenna 17 or other receiver of electromag-' netic waves, is connected through the primary winding of atransformer 18 to a ground 19 as in the usual receiving circuit. The secofflialctromagnetic waves by the antenna.

"illustrated the preferred form of apparatus ondary winding of the transformer 18 is connected through a variable condenser 20 and inductance 21 with the terminals of the coil 1 of the first tube. The inductance 21 is shown as a separate element. It may. of course, if desired form part of the coil 1. The impedances Qand 10 of the plate circuits of the tube form the primary windings of a transformer 22 the secondary windings 23 and 24 of which are connected with the coil 1' of the second tube through the usual capacity and inductance elements; the winding 23 being coupled with the impedance 9 and the winding 24 being coupled with the impedance 10. Similarly the impedances 9 and 10' associated with the plates 7 and 8' of the second tube are coupled with secondary windings 23 and'24' of a transformer 22'.

i The filament circuit is grounded through a connection 25 with the lower end of the antenna circuit and the secondary circuits of the transformers are likewise grounded through connections 26 leading to the wire 25. In each of the connections 26 is a resistance 27.

In operation of the circuit of Fig. 3 electromagnetic waves received by the antenna 17 induce alternating voltage in thesecondary winding of the transformer 18, causing alternating current to flow through the coil 1 andresulting in an alternating magnetic field within the first tube. 1 The alternating field causes variations in the currents through impedances 9 and 10 in opposite directions as heretofore explained. The coupling of the transformer 22 is such that currents varying oppositely in coils 9 and 10 induce voltages in coils 23 and 24 in the same direction. The

current in coil 1 caused by the voltages in-,

riations in voltage occurring in the secondembodying the principle of my new method of using thermionic currents in power amplification. I have also shown one application of such apparatus. My invention is not limited, however, to any particular application nor to the particular design of tube illusave now described my invention and trated. I believe .I am the first to control the distribution of an electronic current by variations in a magnetic fieldin amplifyin devices and as such am entitled to a broa interpretation of my claims. The term al ternating current as employed in my claims is intended to include'broadly any varying current as distinguished from constant direct current and is not intended to' limit my device to the amplification of sinusoidal currents.

I claim:

1. The method of amplifying alternating currents which consists in creating a radial electron flow from a heated cathode to a plurality of anodes equidistant therefrom and positively charged with respect thereto and in controlling the dlStIlbHtIOIl of said flowv to the anodes responsive to changes in a magnetic field created by the current to'be am: plified, while maintaining substantially constant the total electronic current received by all of said anodes.

2. In combination with a vacuum tube having a heated cathode and a pluralityof positively charged anodes, a cylindrical coll adapted to carry alternating current, and surrounding said cathode and anodes and so located with respect thereto as to impress a magnetic field at-right'angles to said elec- 1y with respect thereto to receive the elec-' tronic current therefrom, means within said 1 tube for intercepting a part of said electronic current, means for creatingan alternating magnetic field at right angles to the electronic currentand varying with the current to be amplified. v x I 4. The combination comprising a vacuum tube having a heated cathode for the emission' of an electron flow and a plurality of anodes radially disposed with respect to said cathode for the reception of a constant frac-' tion of said electron flow, a source of electrical energy for charging said anodes positively with respect to said cathode, connections between said anodes and said source each rovided with equal impedances, and a cylin rical coil adapted to carry. alternating current to be am lified and so located as I to impress a mafgnetic field at right angles to sai electron ow.

5. An alternating current amplifying device comprising in combination an evacuated vessel, a filament within said vessel adapted to-be heated to emit an electronic current, a cylindrical shield within said vessel and surrounding said filament, said shield being provided with axial slots of equal width, a plurality of separated electrically conducting anodes forming a longitudinally interrupted cylindrical surface about said shield and coaxial therewith, said anodes being of approximately equal area and of twice the number of the slots in said shield, electrical connections between alternate anodes, 6 means external to said vessel and connecting through the walls of said vessel with two electrically separated anodes for charging said anodes ositively with respect to said filament, and a cylindrical'coil coaxial with said filament adapted to carry the current to be amplified whereby a magnetic field varying with said current may be impressed upon the electronic current to deflect said electronic current and thus to vary the distribution of said electronic current to said anodes responsively with changes in the current to be amplified.

6. Apparatus as in claim 5 wherein equal impedances forming the primary of a transa former coil are rovided in the connecting lines between said external means and said electrically separated anodes.

7. Apparatus as in claim 5 wherein the anodes are so located with respect to the shield 4 that radii from the filament to the s aces between neighboring anodes bifurcate 0th the axial slots of the shield and the sections of the shield between the slots.

In testimony whereof, I have signed my name to this specification. v

MILTON E. THOMSON.

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