US1756481A - Thermionic tube - Google Patents

Description

April 29, 1930. v. BUSH 1,756,481

THERMIONIC TUBE Filed Oct. 1919 3 Sheets-Sheet 1 IIIIIHHHI April 29, 1930. v. BUSH 1,756,481

THERMIONIC TUBE Filed 001:. 7, 1919' 3 Sheets-Sheet 2 April 29, 1930. v. BUSH 1,756,481

THERMIONI C TUBE Filed Oct. 7, 1919 3 Sheets-Sheet 3 iqz'ifizes iatented Apr. 29, 1930 gsa si umrso STATES PATENT] OFFICE VANNEVAR BUSH, OF CHELSEA, MASSACHUSETTS, ASSII IGNOR, BY MESNE ASSIGN- mnnr's,.'ro rownn eaosLEY, 5a., or cmc nnn'rnionro 1 frnnnuronrc runn Application filed-October 7, 1819. Serial No. 829321.

The present invention relates to bulbs employed in connection with oscillating currents, and more particularly to what are known as thermionic bulbs used for detecting,

generating orv amplifying high frequency I l between the filame'nt'and single plate. This currents.

One object of the present invention isi to and improved bulb of this provide a new v character which is not only moreefii'cient in its operation than existin typesof-bulbsbut which may be successfuly employed ina manner impossible with present forms of bulbs.

vide a bulb which, employed particularly as a generator of high frequency currents, has certain distinct and important advantages ever known types of bulbs in use for this purose. With these objects in view, one feature of the invention contemplates the provision in the usual evacuated bulb having a filament and grid, of a plurality of plates connected in a circuit outside of the bulb, which also includes a source of multiphase alternating electromotive force, the number of plates corresponding to the number of phases of alternating E. M. F. impressed upon the plate circuit. v

This form of thermionic bulb permits the employment'of the usual low frequency alternating current of commercial practice for the plate circuit and dispenses with the necessity, as at present, of employing a storage battery of high voltage or some equivalent source of direct current in the plate circuit.

A further feature of the invention contemlates the provision in an evacuated bulb pro vided with the usual filament and .grid, of a series of plates disposed in substantially concentric relation to the filament and grid and connected in a plate circuit having a source of alternating electromotive force correber of phases to the number sponding in num of plates within the bulb. This novel ar- A further object of the invention is to pro .rangement ofthe series of plates within the I bulb has certain important electrical advantages due to the production of a rotating field of electrons between the filament and plates as distinguished from. the usual static field rotating field is due to the fact that the different plates corresponding to the. different phases of the source o'f'energy are alternately charged with positive and negative charges so that the flow of electrons is from the filament to successive plates, this flow being governed by the phase relation of the alternating potential impressed upon the plate circuit. Among other advantages the use of a series of plates in a single bulb rather than a series of separate bulbs permits the employment of a common filament operating withthe individual plates in turn, thus requiring less filament energy and resulting in a higher eficiency for: the bulb.

Still further features of the invention consist in certain novel features of construction, combination and arrangement of parts hereinafter described and claimed, the advantages of which will be obvious to those skilled in the art from the following description.

In the accompanying drawings, Figure 1 is a view in elevation with a portion broken away and showing in section the new bulb forming the basis of the present invention.

Fig. 2 is a detail showing a cross-section of bulb employed as a detector with the proper circuit arrangement and with a six-phase source of energy for the plate circuit. Fig. 6 is a diagram of the six-phase alternating E. M. F. supplied by the transformer together electron source and subdivided into a number,

of parts. The source of energy for the plate circuit is a multiphase trans-former corresponding in number of phases to the number of plates within the tube. Interposed between the heated filament and plates is agrid consisting of a fine wire, through which the electrons have to pass to get from the filament to the plates. The several plates are located in concentric relation with respect to the filament and grid and in such a manner that a rotating field ofelectronsis established between the filament and successive plates.

As shown in the illustrated embodiment of the invention indicated in Fig. 1, the improved thermionic bulb comprises an evacuated receptacle or tube 2 within which are mounted a filament 4, a plurality of concentrically supported plates 6, 8 and 10 (three of which are shown in Figs. 1, 2 and 3, and six of which are shown in Fig. 5). These plates practically surround the filament and inter posed therebetween to cut the field of electrons is a grid 12 of fine wire preferably wound as a spiral. Upon referring to Fig. 3 of the drawings it will be observed that the three parts of the plate are connected in circuit with .the secondary of a three-phase transformer, indicated generally at 14. This transformer secondary as shown has the usual Y connection with the three legs 16, 18 and 20- connected respectively to the plates 6, 8 and 10. The neutral or middle point 22 of the transformer secondary is connected to the filament 4 through part of an inductance 26. The inductances 26 has a capacity indicated at 28 connected across it, and in addition each leg of the transformer secondary has a capacity 29 connected across it. The circuit from the middle point of the transformer secondary to the filament through part of the inductance 26 may be providedwith a key 24 to open and close it. It will be observed from an inspection of this figure that the circuit arrangement shown is suitable for the employment of the bulb as a generator of electrical oscillations, the grid 12 being connected in the usual manner through a circuit indicated at 31. The essential difference between the present arrangement and that normally employed-is the use of the multiphase source of energy in the plate circuit in place of the usual high voltage storagebattery of constant potential. With this multiphase source of ener the plate current flows through each of t e plates in turn, in such a manner that an almost constant current passes through the neutral point 22 of the transformer secondary. Fig. 4 of the drawin illustrates by the curves 30, 32 and 34, t e

voltage impressed upon the plate circuit by voltage waves 30, 32 and 34. This current,

as will be evident, is not wholly constant, but has a slight variation or ripple determined by the number of phases in the source of supply and the frequency ofv the supply. As will e observed from an inspection of Fig. 6 of the drawings, in which 52 reperesents the current flow in the plate circuit with a six-phase source of supply, the ripple may be reduced in part by increasing the number of phases of the supply.

In practice the filament 4 may be heated to incandescence through a local circuit indicated at 40 which receives energy from a storage battery 41 of constant potential;

As stated, the employment of a multiphase source of energy for the plate circuit causes a ripple in the current flow through the plate circuit depending upon the number of phases and the frequency of alternation of the supply. This ripple in the plate current will vary the amplitude of oscillation of the bulb. If such a bulb then is employed for the purpose of transmitting radio waves, the amplitude of the radiated waves will also vary periodically in a like manner. In case it is desirable or essential to cause the bulb to oscillate with a constant amplitude of oscillation, this may be accomplished by suppressing the slight variation or ripple which normally ocours in the plate current. The suppression of this ripple in the plate current is also desirable if the bulb is to be employed as a detector, the circuit for which is indicated in Fig. 5 of the drawing. Accordingly, means have been provided for suppressing the variation or ripple in the plate current to such an extent that the latter will be substantially constant except during the reception of incoming signals. In the best form of the invention now known this is accomplished by varying the wave form of voltage generated by the source of supply, so that instead of the usual sinusoidal form of wave, the transformer secondary supplies a peaked form of waveI When this form of wave is supplied, the ripple in the plate current, indicated at 36 and 52, is substantially suppressed. The fact that a peaked wave form of voltage sunplied by the transformer produces a substantially constant plate current has. been demonstrated and proved mathematically. This form of voltage wave is indicated at 45, Fig. 7 of the drawings, and the effect of combining such wave forms is indicated at 47 in the same figure. It will be observed that the plate current indicated at 4.7 is substantially constant. As a matter of fact, the constants may be so designed that the ripple remaining in the plate current is less than one per cent. With the conditions as outlined, employing a peaked ,wave form of voltage supply, the oscillations of the bulb can be made substantially constant in amplitude making the latter suitable for the purposes of radio telephony.

Assuming that this form of bulb is used for transmitting purposes and that a threephase transformer is employed in the plate circuit to supply voltage at a frequency of sixty cycles, then the radiated waves will pulsate at a frequency of 180 cycles per second. If a six-phase transformer is used in the plate circuit with the same frequency, in that case the waves will be radiated at a frequency of 360 cycles. It should be understood that the frequency of radiation in both cases will be fixed and determined by the constants of the circuit although the amplitude of these radi-' ated Waves may vary.

A function of-the present bulb which may be important in certain instances is due to the pulsating current in the plate circuit which causes radiations from the-system that may be received without the necessity of chopping of heterodyning. In case the bulb is used in this manner, it may be advisable to accentuate these currents in the plate circuit rather than to suppress them. This may be accomplished by operating the bulb at such a part of the characteristic that a change in the plate current causes a correspondingly 7 large change in the amplitude of oscillation.

Figure 5 illustrates diagrammatically the employment of the bulb as a detector with a proper circuit arrangement. In this case also a six-phase transformer is incorporated in the plate circuit with the use of 3. corresponding number of plates. The transformer secondary is indicated at with six legs connected to a neutral point 71, each of the legs being in addition connected to the six sections of the plate. 'The neutral point 71 of the transformer is connected to the filament 4 through a circuit containing the usual telephone receiver 7 4. The local circuit for heating the filament is indicated at 75 and includes the usual constant potential battery 76. The grid is connected through the circuit 78, including inductance and capacity connected in parallel and indicated at 79, through which oscillations are adapted to be inductively received from an antenna. With this circuit arrangement, the oscillations impressed upon the grid circuit set up pulsations in the filament plate circuit which may employing the bulb .as a detector, the ripple normally present in the plate current, due to the use of alternating sources of energy, may be suppressed by using a peaked wave form in the supply as hereinbefore set forth, and by circuit arrangements for eliminating undesirable frequencies as well known in the art.

It Will be understood that the invention in its broader aspects contemplates the use of any desired multiphase source of alternating potential in the plate circuit. For example; it has been found that a source of ener having two phases may be successfully used when combined with some means for suppressing the consequent fluctuation in plate current. It will be obvious that with a two phase source of energy as described, having the voltage waves 90 apart, the plate current will periodically rise to a maximum and fall tozero. These fluctuations in plate current may be largely suppressed by suitable control of the grid circuit. This method is of advantage from the practical standpoint because of the extreme simplicity of the transformer and connections for producing the two phase potential.

Briefly stated, the invention contemplates the use of a single thermionic tube for serving the double purpose of operating in the manner of the usual thermionic tube, and also for supplying its own rectified plate current. The tube employs working circuits constituting an input and an output circuit which are of the type ordinarily associated with a thermionic tube. Thus in the oscillator assembly of Fig. 3, the input and output circuits are made up of portions of the inductance 26, together with the condenser 28, while in Fig. 5, the input circuit is the resonant circuit 79 and the output circuit comprises the telephone 74. It will therefore be seen that the single tube operates with the usual input and output circuits whereby the oscillations in the output circuit are controlled by the oscillations in the input circuit and at the same time it furnishes its own rectified plate 'supply, thereby... eliminating the necessity for separate devices'for power supply and operation of the working circuits.

Having thus described the invention, what is claimed is 1. A thermionic tube circuit comprising a thermionic tube having a filament, a grid, and a plurality of plates, input and output circuits associated with the grid and plates respectively, and means for energizing the plate circuit comprising a multiphase source adapted to have its separate phases connected with the separate plates, the multiphase source being arranged to deliver a voltage of peaked wave form to maintain the excitationof the plate circuit at a substantially constant value. 2. :A thermionic tube circuit comprisin a single tube having a filament, a grid an a 5 jplurality of plates, means for energizing the lament, an input circuit associated with the rid, a plate circuit, an output circuit associated with the plate circuit, and means for energizing the plate circuit including a multiphase alternating current source having the separate phases connected to the separate plates.

VANNEVAR BUSH.

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