US2411362A - Shaped amplifier - Google Patents

Description

Nov. 19, 1946. J. R. BOYKIN 2,411,362

SHAPED AMPL IFI ER Filed April 1, 1944 fimll LIIIF A WITNESSES:

MWM

INVENTOR John R Boykin.

ATTOR Patented Nov. 19, 1946 UNITED- STATES PATENT OFFICE SHAPED AMPLIFIER John R. Boykin, Baltimore, Md assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 1, 1944, Serial No. 529,109

4 Claims. -(Cl. 179-171) My invention relates to electronic amplifiers and, in particular, relates to the reduction in the ripple produced in the output current of such amplifiers by causes such as the effect of alternating heating current for the cathode, fluctuations of cathode emission and the like. It is particularly applicable to amplifiers having cathodes directly heated by alternating or pulsating current of a frequency greater than that impressed from the input circuit of the tube.

For certain purposes in the electronic art, it is desirable to use electron tubes having cathodes of what may be termed U-shape which are directly heated by alternating current. It is also known that such alternating-current heating tends to produce fluctuations of the output circuit current which may be referred to as hum which are naturally in undesirable interference with the action of the tube when it is used, to amplify a signal input current. In the prior art, the magnitude of this hum has been greatly decreased by connecting the common terminal of the control-electrode circuit and the plate circuit to a point on the heater circuit which is at the mean value of the potential between the cathode terminals. This connection is usually made by attaching the control electrode and plate circuits to the midpoint of a resistor which spans the cathode terminals. It is also known that hum effects are produced by the magnetic field and the potential drop along the filament between the terminals of the cathode; and that by properly proportioning the magnitude of these efiects, their resultant hum in the output circuit can be nearly eliminated.

. However, it is frequently impracticable to make the point of attachment to the resistor spanning the cathode terminals at its exact electrical mid-* point, and likewise impracticable in quantity production to produce tubes in which the other sources of hum above mentioned are ideally reduced to zero.

In accordance with my invention, however, I have found it possible to substantially eliminate the residual hum eifects mentioned in the preceding paragraphs by the circuit connections shown in the drawing and about to be described.

One object of my invention is, accordingly, to

provide circuit connections for an electronic amplifier having a cathode filament heated with alternating current which shall enable the tube to eificiently amplify fluctuating voltages impressed on its input circuit, while at the same time sub- 2 put circuit which otherwise would be produced by the cathode heating current.

Another object of my invention is to provide a circuit for an electronic amplifier tube which shall make it possible to effectively amplify fluctuating currents impressed upon its input circuit while at the same time substantially eliminating fluctuations in its output circuit due to fluctuations f electron emissivity of its cathode.

Still another object of my invention is to provide a circuit for electronic amplifier tubes having cathode filaments directly heated by alternating current of a frequency greater than the voltage fluctuations impressed on their input circuits and which shall amplify the last-mentioned voltage fluctuations, while at the same time substantially eliminating the hum in their output currents which would normally be caused by their cathode heating currents.

Other objects of my invention will become apparent upon reading the following description, taken in connection with the single figure of drawing which illustrates a three-electrode electronic amplifier tube connected up with a circuit embodying the principles of my invention.

Referring in detail to the drawing, an electronic amplifier tube l, which may be of the highvacuum type and is shown here as embodying an anode 2, a control electrode 3 and a cathode 4, comprising a U-shaped electron-emissive filament 4 is supplied with alternating heating current from an alternating current source 5. To take one example, the frequency of the source 5 may be 800 cycles per second. The terminals of the filament 4 immediately outside the tube l are spanned by a resistor 6 having a tap I positioned as closely as possible to its electrical midpoint.

An input transformer 8 impresses a fluctuating:

signal voltage which may, for example, have a frequency of 150 cycles'per second in the control electrode 3 by means of its secondary winding 9, one terminal of which is connected to the control electrode 3 and its other terminal connected through a bias battery I l to the above-mentioned tap 1.

The flow of the alternating heating current through the cathode 4 will alternately make the stantially eliminating the hum efiects in its outrespective end terminals thereof positive and The anode 2 is connected through a 're-Q sistor l2 to the positive terminal of a voltage tween them; If the tap point 1 is exactly at the electrical midpoint between the terminals of the cathode it, it will likewise remain at the same fixed potentiala's the midpoint of the cathode itself, and under such circumstances, no voltage having the frequency of the supply 5 is effectively 7 .I impressed between either the control electrode 3 or the anode 2 and the cathode 4. However, if

the tap point I is displaced from the electrical midpoint of the resistor 6, a-voltage having. the

frequency of the supply 5 can be shown to be an anode, at least one control electrode and an impressed between both the control electrode 3 and the anode 2 and cathode 4. This will result in the production in the output resistor '12 of a current having the frequency of the source 5.

.In acco da wi h my nvention I conne t. a capac t 1 een the. epnt p le trode 3. a he e e e This. ffec ma e he. tube, 1 actl s rea tance t be. and in er eses between he. qn q 1? ra 3 and the c hode. 4 an efie ti e c pa t nce. which equa to ILC, where C is t e. a acit c of he capa i r i5, a d P! s he. v lta e am ification o the. e ectro tube. I The i duetanc of e se ondary i in t. is reierably tuned. wit t is ect ve apa itan e reso e. at he f equ ncy impressed by th ensi m r 8.; e.- t e. present exampl i un d. to. e onate t .50 ycles.

Under such ci cumstances, the. secondary nd-- t and th apac t r i can beshown to on.- itutea ow-pass. fi t r of theL type. for c r ents. hav ne he f uency of the supply source. 5,, and wra s higher arm ics ther of. Because Of the resonance to the frequency supplied through e. trensi rmer 8, the v ta e. fluctua ions that frequency of the control electrode 3 relative Q ClQ. cat ode 4.- approximate a maximum. The mpedance o t see ndary winding e t currents of the frequency of the. supply source. 5. is, how.-

ever, uch lar er than he'efiectiveim e e of; the capacitor [5, so that thesecondarv windnnfiiatts n. effect, to. chok the flow. of h at n resip cur e t thrqueh the c itor lined th c s, ike. a QWrimDBQfiI s u t. by-.

' esti .vqltae sp that e uen y r m. t e p between ee t plelett qde 3 en he ca hodet. ent nd r. uch c rc mstance that t i ed he. ee e lter and; nduc anc of: w ndi 9;,- wil t ee a eve mere efiett re len -pa s filterer re e eler er hen hpseqt he eetme some. 5, 814th, or. e m le, e seed harmonic thereof which may be due to magnetic e'ifcts of. the cat de heating current and to. voltage drop." along the cathode 4, between its te m a s h e r lr s a em n a feet. be". madethatthewindIngQQand the capacitor l5 wiutenu. tjoichoke out. from t output circuit of em ee; 4.,

. c ntr ermite tube I, such, for example, 'asjthose due to. random fluctuations in electron em ssion? from" the The arrangement of the capacitor l5 and the secondary winding 9 may be considered to constitute an inverse feed-back from the plate circuit to the grid circuit which tends to increase the stability and'decrease distortion in the amplifier I. This inverse feed-back will, in fact, tend to reduce the effect of disturbances in the plate circuit of the tube I.

' In accordancewith the provisions of the patent statutes, I have described a particular embodiment of the principles of my invention, but these principles are obviously of broader application in ways which will be evident to those skilled in the art. 7

- I claim as .my invention:

1. In combination with an electron tube having electron-emissive cathode, an inductive winding connectdbetween said control electrode and said at the frequency of input voltages impressed on said winding with n times the capacitance of said capacitor, where n is the voltage amplification of said tube.

2. In combination with an electron tubehaving an anode, at least one control electrode and an electron-emissive cathode, a circuit for heating said cathode from a source of periodic current, an inductive winding cojn i ected between .said control electrode and a point on said circuit, an output circuit connected between said anode and the last-mentioned point, and a capacitor connected between said, control electrode and said anode.

3. In combination with an electron tube having an'anode, at least one control electrode and a cathode heated by periodic current of a predetermined frequency, an inductive winding connected between said control electrode and saidcathode,.means for impressing on said winding aperiodic voltage which has a frequency lower than said predetermined frequency, an output circuit connecting saidanode to said cathode, and a capacitor connected between saidcontrol electrode and said anode;

4. Incombination with an electron tu-be'having an. anode, at least one control electrode and a cathode heated by periodic current of a predetermined: frequency, aninductive winding connected between. said. control. electrode and-said cathode, means for impressing on said winding a periodic voltage which has a frequency lower resonate at; saidlower frequency with. timesthe capacitance of;- said capacitor, where. ,c .is. the

voltage. amplif cation. of, said tube.

JOHN- Rt BdSYKIN:

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