US2790036A - Electron-tube stabilized amplifying circuit - Google Patents

Description

April 23, 1957 B. H. TONGUE ELECTRON-TUBE STABILIZED AMPLIFYING CIRCUIT Filed June 7, 1955 OUTPUT INVENTORQ BEN mucus INPUT ATTORNEYS;

ant i'rnore particularly, re raaiqfre 'such techniques as 'utilifziiigdegeneratioh f provide a new "and i prove meme -tribe cathode, control gamma-scream H todes. In summary, this end is 9. Inc

United States Pa 1,756,031; ELECTRON TUBESTABILIZED AMPIJIFYING CIRCUIT BenH. i*6n 1ie, vVestfiil, N. J. Application June 7, m ss-serial1%:512 808 e'olaiin's. (01. 179471) "re electron-tube circuits r n w 'bodyin'g electron tubes having at lea-st five electrodes, such as pentodes. n

u In many present-day electron- A or vacuum-tube radiofrequencyiamplifier circuits, and p rt'eur' l p loying pento'des, deleterious: ef-t'unln'g and bandwidthif'aiiaition effects take "place as "thega'in of the 'tube is varied. This ale-tuning eifect is caused by improper neutralization of feedback between the outputand ir'iputpirfeedback effects in pentodes and reso e in the screen grid-to-c'athode"circuit. V

An obiect of the present invention, accordingl'yfis'tb shallfn'ot be Subject to "either 255 the above' deleterious e'ifec'tso'f de-tiiningohbandiwidth When n.

A further object is to p rovide a newan p entode electron-tube circuit f th' at 's ir nulta'njeo 1 y pensates not only for"alhfeedbaclgeifectsi quency pentod'e anipl'ifieifs'but also foriie g'ativej sistance effects resulting from the' triode' operation pen sesribe a circuit connection from fthe 'f scr ground having negligible radio-fi e V by resonating out the i' d tanc'eof'thefsc e input circuit through the anode-ito-s trade and suppresscr-grid electrode-to-contiol-grid 615etrode capacitances, substantially sire undre d eighty degrass 'with respect to the phas e o f theiradiofieguencyienergy fed from theoutput to thrbughthdaiicideto-cont rol-grid electrode capacitance.

, n q -k di iihtf.Nes s. wi llb j ir e f i iii iir anti will be more particularlypoiiited but in the appended claims The invention will now be describled in connection 'with the accompanying drawing the single figure' of v'vhich is aschematic circuit diagram illustrating the invention in preferred fer-m. H

A conventional'pentode electron tube or vacuumtube, as of the beam type, is schematically shown at -1 provided with an electron-emitting cathode electrode 2, a controlgridelectrode 3, a screen-gridelectrode '4, a suppressor- 'grid ele'ctrod'e'S and a plate or 'anode'electrode 6. A source of anode potential or voltage is applied between the anode sand the cathode 2, the pos""' ve or B -lterininal of the voltage source heiiig'conn" ted, p 'fer'abl'y through a radio-fre'que'ncy choke, not sh wn, ode 6, and the negative or B-tirriihzil Being co I through cathode-load resistors 7 and '9 to'the cathode'Z. The B terminal may be connected to ground, 'asis'hovv'n, if desired. The term groundfindeed, as utiliz'ed'in'tliis specification and in the claims, is'in'tended tobonfiote 'iiot only actual earthin'g, but chassis or any other reference potential. Inorder not to detract from ithe f'ature's of novelty, the well-known details'of'tlie voltage's'ourcesffor :the "electrodes and other circuit refinements'are not illustrated. i V v Connected between the anode 6 andlcathode Z is an outpufcircut Zm'pu Similarly, an input ircuit Z nes may be connected between the B' ftemiih'al a the centiol grid electrode 3 by 'conductojrsti and lfi,fespctively. The input and eut'pm circuitsai eshown in generalized bl' shk-diagrmn form'sinee the presen invention ma be utilized with any desired type of radio frequency circuits,

input and output circuits. "As "an 'il1tistration, 4 and output circuits may' comprise res ant a vvorks s'uch 'a'sQshurit or series-connected e mbinar ris ifi'du ctzlirice tiiidfc'apacitanee, "sir-awn. Tne',,,.mjb a j p'n'teue stage may be varied b'y varying the amount o'f 'hegative bias vol age applied 'rtoin a source of saga e potential -vie through apotentiometer 11, and 'a 'd to th eantrergna electrode '3. 'I he r or 12. 1s 'slrovvn aadhpied to ground by a lay-passe denser '13. The bias voltage may, of' course, be co o'll'd autiimaticaily by fa'n automatic gain control circuit, as ell ever, fromthe plate or ano'de6 totli' A through the inherent anode toscFen-grid :electr'o'de "eapacitarice C 35 and the'screen-grid"electfode to controlg rid electrode capacitance C 'It'haslbefore scanneprised tomininiize the feedback aloii'gtli'e path CnsQC-S'}; by jgrou n ding the screen-grid electrodef4. Miriiiniiiiig of the feedback effect alongthe'p'ath C 'lias'lpeen"attempted through elaborate shielding 'h'etwen the grid anaem a connections. 7 v v -Untortur' ately, however, at the higherradio' freqiiencies above, say, tens of megacycles, the physi'c'al"s'tfictureiof the screen grid4 in conventional Pen'tods. and the I'lie and of the above desc'ribed connection theref 'gr'cund, even iflrept veryshort, may present a s ubs't ntial inductive reactance Neutralization aloirglthepath Cps, Q e y these P i r mas es i thuvs a bl t frequenciesin view of the fact that-this inductiye rea ssn P n i l. isi'lt isia tsfi s l vs hi d. e wee p 1 2 M i? P??? thi awe :thP. f n si i Estate? Qpie sfisti.at.Pgi i e iq s qnqi s r -Phys 'ical structure of the screen grid 4 and the connection thereof to ground produces the earlier-mentioned further circuit.

a negative input resistance of the tube, results in a change in the radio-frequency loading of the triode portion 2, 3, 4 of the pentode 1. This loading change will produce a corresponding change in the Q of the input circuit Zinput and hence will result in an undesirable variation of the bandwidth of the input In accordance with the present invention, the matter of rendering the feed-back path cps, Csg ineffective and of obviating the bandwidth-variation effect in the triode operation of the portion 2, 3, 4 of the pentode, is accomplished in the following way. Though it is not possible to ground the physical center of the screen grid 4 directly,

since the grid is within the envelope 1, this result is effectively achieved electrically by resonating the inherent inductance L of the structure of the screen grid 4 and the inductance of the physical connection to ground from the terminal of the tube socket, not shown, in which the tube 1 is mounted, with appropriate series-connected capacitance C. This resonance at the desired radio frequency places the screen grid 4 at radio-frequency ground and effectively shields the capacitance cps from the capacitance Csg, thereby preventing feedback energy from passing therebetween. In addition, however, this resonance has caused the impedance between the screen grid 4 and ground to change from a reactance, the effect of which caused a negative input resistance, into substantially a low resistance with negligible reactance. now negligible impedance between the screen grid 4 and ground, the radio-frequency loading of the triode portion 2, 3, 4 of the pentode 1 will not change with change in gain of the pentode and the undesirable bandwidth-variation effect is simultaneously substantially eliminated, also.

It now remains to vitiate the effects of the feedback path including the capacitance Cpg, which may have a very small capacitance value of, for example, 0.02 micro- Since there is microfarad. This could theoretically be done by utilizving a large parallel-connected inductor; but, in actual practice, particularly at high frequencies, it is not feasible to construct such a large inductor that willnot inherently have'dis'tributed capacitance which is even greater than the small-valued capacitance cpg. In ac- 'cordance with the present invention, therefore, an entirely different technique is employed. A circuit connection 16 is made from the suppressor-grid electrode 5 to ground through an inductance Ll of sutficient value to produce a predetermined shift in the phase of the radiofrequency energy of the desired frequency fed from the anode 6 through the anode-to-suppressor-grid electrode 1 capacitance C; to the suppressor grid 5. The amount of phase shift required is that which will bring the energy fed from the suppressor grid 5 to the control grid 3 through the suppressor-grid electrode-to-controlgrid electrode capacitance C2 in substantially phase opposition to (i. e. substantially one-hundred eighty degrees out of phase with) the energy coupled back from the output to the input through the interelectrocle capacitance Cpg- The one-hundred eighty degree out-ofphase voltage at the suppressor grid 5 will cause a current to flow through the suppressor grid-to-control grid capacitance C: to the control grid 3 which is substantially equal and opposite to the current flowing from the anode 6 to the control grid 3 through capacitance Cpgflows from the output to the input circuit. To achieve such a phase shift, the reactance of the inductance Li at the desired high frequency will be made smaller than the reactance of either of the interelectrocle capacitances Ci or C2.

The result is that substantially zero net feedback current As an illustration, the above results can be achieved with a 6CB6-type pentode operating with input and output circuits tuned in the neighborhood of about 200 megacycles with an inductance L1 formed of about a one-inch loop of number twenty-four wire. The screengrid resonating capacitance C may have a value of about 39 micromicrofarads and the length of the conductorlead 15 may be about one-eighth of an inch.

At much lower frequencies, the reactance of the screen grid 4 and its connection 15 to ground may be sufficiently negligible that a direct short connection 15 may suffice without the necessity for the resonating capacity C. While the plate-to-control grid feedback will then not be reduced to so low a value as can be attained with the resonating capacity C, the results may, in some instances, be adequate. It is also to be understood that external neutralizing elements could be employed to replace the interelectrode capacitances and the suppressorto-ground inductance, but since such external elements would increase the tube input and output capacitance and thus reduce the gain, this is not a preferred construction.

Further modifications will occur to those skilled in the art and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. In an electron-tube circuit for operation at a predetermined radio frequency having at least five electrodes, namely, an anode, a grounded cathode, a control-grid electrode, a screen-grid electrode and a suppressor-grid electrode, and radio-frequency input and output circuits connected from the cathode to the control-grid electrode and to the anode, respectively; the combination of a circuit connection from the screen-grid electrode to ground having negligible impedance at the said predetermined radio frequency, and a circuit connection from the suppressor-grid electrode to ground having an impedance of 'suflicient reactance at the said predetermined radio frequency to shift the phase of the radio-frequency energy fed from the said output circuit to the said input circuit through the anode-to-suppressor-grid electrode capacitance and the suppressor-grid electrode-to-control-grid electrode capacitance substantially one hundred eighty degrees with respect to the phase of the radio-frequency energy fed from the said output circuit to the said input circuit through the anode-to-control-gr id electrode capachance.

tance from the screen-grid electrode-to-control-grid electrode capacitance, means for presenting a negligible impedance at the said predetermined radio frequency between the screen-grid electrode and ground, and a circuit connection from the suppressor-grid electrode to ground having an impedance of sufficient reactance at the said predetermined radio frequency to shift the phase of the radio-frequency energy fed from the said output circuit to the said input circuit through the anode-to-suppressor- 3. In an electron-tube circuit 'for'operation at a predetermined radio frequency having at least five electrodes,

namely, an anode, a grounded cathode, a control-grid electrode, a screen-grid electrode and a suppressor-grid electrode, and radio-frequency input and output circuits connected from the cathode to the control-grid electrode and to the anode, resspectively; the combination of a circuit connection from the screen-grid electrode to ground provided with capacitance of suificient value to resonate at the said predetermined radio frequency with the inductance in the said circuit connection, including the inductance of the screen-grid electrode itself, in order not only to ground the screen-grid electrode but to do so through a circuit of negligible impedance at the said predetermined radio frequency, and a circuit connection from the suppressor-grid electrode to ground provided with inductance of sufficient value to shift the phase of the radio-frequency energy fed from the said output circuit to the said input circuit through the anode-to-suppressor-grid electrode capacitance and the suppressorgrid elcctrode-to-control-grid electrode capacitance substantially one hundred eighty degrees with respect to the phase of the radio-frequency energy fed from the said output circuit to the said input circuit through the anode-to-control-grid electrode capacitance.

4. In an electron-tube circuit for operation at a predetermined radio frequency having at least five electrodes, namely, an anode, a grounded cathode, a control-grid electrode, a screen-grid electrode and a suppressor-grid electrode, and radio-frequency input and output circuits connected from the cathode to the control-grid electrode and to the anode, respectively; the combination of a circuit connection from the screen-grid electrode to ground having negligible impedance at the said predetermined radio frequency, and a circuit connection from the suppressor-gridelectrode to ground provided With inductance of reactance at the said predetermined radio frequency less than the reactance of the anode-to-suppressorgrid electrode capacitance and of the suppressor-grid electrode-to-control-grid electrode capacitance but sufficient to shift the phase of the radio-frequency energy fed from the said output circuit to the said input circuit through the anode-to-suppressor-grid electrode capacitance and the suppressor-grid electrode-to-control-grid electrode capacitance substantially one hundred eighty degrees with respect to the phase of the radio-frequency energy fed from the said output circuit to the said input circuit through the anode-to-control-gn'd electrode capacitance.

5. In an electron-tube circuit for operation at a predetermined radio frequency having at least five electrodes, namely, an anode, a cathode, a control-grid electrode, a screen-grid electrode and a suppressor-grid electrode, and radio-frequency input and output circuits connected from the cathode to the control-grid electrode and to the anode, respectively; the combination of a circuit connection from the screen-grid electrode to ground having negligible impedance at the said predetermined radio frequency, a circuit connection from the suppressor-grid electrode to ground having an impedance of sufiicient reactance at the said predetermined radio frequency to shift the phase of the radio-frequency energy fed from the said output circuit to the said input circuit through the anode-to-suppressor-grid electrode capacitance and the suppressor-grid electrode-to-control-grid electrode capacitance substantially one hundred eighty degrees With respect to the phase of the radio-frequency energy fed from the said output circuit to the said input circuit through the anode-to-control-grid electrode capacitance, and a cathode load connected between the cathode and ground and part only of which is by-passed to ground.

6. In an electron-tube circuit for operation at a predetermined radio frequency having at least five-electrodes, namely, an anode, a cathode, a control grid electrode, a screen-grid electrode and a suppressor-grid electrode, and radio-frequency input and output circuits connected from the cathode to the control-grid electrode and to the anode, respectively; the combination of a circuit connection from the screen-grid electrode to ground having negligible impedance at the said predetermined radio frequency, a circuit connection from the suppressor-grid electrode to ground provided with inductance of reactance at the said predetermined radio frequency less than the reactance of the anode-to-suppressor-grid electrode capacitance and of the suppressor-grid electrode-to-control-grid electrode capacitance but suflicient to shift the phase of the radio frequency energy fed from the said output circuit to the said input circuit through the anode-to-suppressor-grid electrode capacitance and the suppressor-grid electrode-to-control-grid electrode capacitance substantially one hundred eighty degrees with respect to the phase of the radio-frequency energy fed from the said output circuit to the said input circuit through the anode-to-control-grid electrode capacitance, and a cathode load connected between the cathode and ground and part only of which is bypassed to ground.

References Cited in the file of this patent UNITED STATES PATENTS 2,093,094 Peterson Sept. 14, 1937 2,200,055 Bornett May 7, 1940 2,533,020 Knol Dec. 5, 1950

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