US2412314A - High-frequency apparatus - Google Patents

Description

fDeC- 10, 1946- T. J. BoRNl-:R ETAL 'HIGH FREQUENCY. APPARATUS Filed June 17, 45

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Dec.1o,1946. T. J. BOERNER Em 2,412,314

HIGH FREQUENCY' APPARATUS /l Trop/v5 y "Dea 10, 1946. T. .LBOERNR ETAL 2,412,314

HIGH FREQUENCY APPARATUS `Filed AJune 1'17, 1943 8 Sheets-Sheet 4 //v VEA/709,5' Tho 0.190 ernen Jcn, ,Sanbo'zv ATTORNEY Dec. 1o, 1946. T J BOERNE'R FAL 2,412314 4 HIGH FREQUENCY APPARATUS 8 Sheets-Sheet 5 Filled June 17., 1945 Dec. l0, 1946. T, J. BOERNER ET AL 2,412,314

HIGH FREQUENCY 4PPARATUS Filed June 17, 1945 8 Sheets-Sheet 6 l /M/-/vro web l Dec. l0, 1946. T. J. BOERNER E-rAL 2,412,314

HIGH FREQUENCY APPARATUS Filed June 17, 1945 8 she'ets-sheet 7 IN1/EN Topp o armer anb Dec. 10, 1946. T. J. BOERNER ETAL HIGH FREQUENCY APPARATUS -8 Sheets-Sheet 8 Filed June 17, 1943 Patented Dec. 10, 1946 Y' HIGH-FREQUENCY APPARATUS Thomas James Boerner, Collingswood, and John W. Sanborn, Merchantville, N. J., assignors to' Radio Corporation of America, a corporation of Delaware Application June 17, 1943, seria1N0.491,164

11 Claims.

This invention relates to high frequency'ap- `paratus and especially to the power amplifier stages of high frequency transmitters.

Oneobject of the invention is to provide improved high frequency vacuum tube power amplifying apparatus and circuits which shall operate at high efficiency and'- in which spurious effects such as parasitic oscillations are minimized,v A further object of our invention is to provide high frequency amplifying apparatus wherein the frequency of operation may readily and conveniently be changed. Y

A further object of the present invention is to provide an improved high frequency tank circuit for vacuum tubes. A feature of the tank circuit resides in an arrangement of fixed and relatively movable conductors Awhich are so connected and arranged as to form a variable inductor for the tank circuit. In this` regard provision is `made for varying the spacing between the conductors of the inductorsystem, thereby .varying the effective inductance connected into circuit. y

A further object of the present invention is to .provide an improved high frequency output cirarrangement may readily be adjusted for operation over avwide range of frequencies,

In brief, certain features of the present invention may be outlined as followsz* A push-pull connected vacuum tube driver stage is coupled through a condenser-divider arrangement to a push-pull connected vacuum tube power amplifier. The condenser-divider operatesin such a way that over a wide range of operating frequencies substantially constant radio frequency excitation is applied to the grids of the y power amplier with constant direct current voltagev impressed upon the plates of the driver tubes.` Y

2 n secure iiow of equal grid currents over a operating range.

The tank circuit of the power amplifier generally consists of a pair of conductors fixed in position, having substantially uniformly distributed inductance and capacity and another -pair of similar conductors insulatingly supported upon a movable metallic plate. These xed and movable conductorsV having uniformly distributed electrical capacity and inductance are connected together by exible straps. Mechanical instrumentalities `are provided for moving the metallic plate upon which the movable conductors are mounted so that the effective separation of the conductors may be varied, thereby varying the effective inductance ofthe tank circuit. As the conductors of the tank are moved closer together, the inductance is increased and, similarly, as the separation between the conductors is vincreased the inductance of the tankcircuit is decreased.

A final output circuit is provided coupled to the tank circuit. This final output circuitalso makes use of conductors having substantiallyuniformly distributed inductance and capacity forming the effective inductance of the output circuit. Variable and fixed condensers are also provided which form part of the output circuit. The units of the output circuit are mounted as `a single unitary assembly which may be variably couwide Apled to the tank circuit without substantially changing the tuning ofthe output circuit and, furthermore, instrumentalities are provided for changing the tuning of the output circuit without substantially altering the coupling thereof with the tank circuit of the power amplifier. I

vReversible electric motors are provided for adjusting neutralizing and tuning condensers ofthe power amplifier stage and output circuit. Further instrumentalities under control offother reversible electric motors are provided for adjusting the separation of the conductors ofthe tank circuit and, hence, the effective electrical inductance thereof and also for adjusting the coupling between the output circuit assemblyand the tunable tank circuit. Limit switches' are provided for the motors so as to prevent` them Vfrom over-running in either direction. Instrumentalities are also provided'whereby each Areversible electric motor drives the variable arm of a potentiometer. Each potentiometer supplies voltage to a separate tuning indicator which may be in the form of a volt meter. In vthis way the tuning indicators give a measure, by theA respective volt meter readings, of vthe capacityin circuit and'in other cases the amount of couwhich the tank circuit is couplj constituting the power amplifier 'frequency mum 'ftiibe'se'IjY'lfand IVe-appears in the'tuned'output pling or the amount of inductance in the power I amplifier tank circuit.

In the drawings:

Figure 1 is a wiring diagram of a push-pull' connected driver-amplifier stage feeding through a condenser-,divider arrangement the gridsrof a pair of push-pullz'connected vac'uumtube amplii- A ers of a high frequency power amplifier'. As il'` lustrated in Figure 1, reversible electric motora are provided for varying neutralizing and tuning condensers, the inductance of the tankfcircuit,

and the coupling between the tank dcircuituof the power amplifier and the final 'o "i I 1;; Figure 2 is a side elevational "view of apparatus al view ofthe apin'to thesecondary ILISQ'eXcitingthe control grids tubesIVfI and IVSinjphas'e opposition. The carrier 'may be generatedrby any suitable vac'- uum tube generatorfollowed by amplifiers vand pliers y ,'I-fhesecond'aryj ILI3 is tuned bythe split 'statorgjcoiidenser I CkiII.. The

"circuit comprising'coil IL IB and condense'rs I CI Il I into-the `circuit'las' needed, depending regnen@ employed-f if der to prevent `spurious osc'zillations,` the ds of the" Idriver Y tubes j'IViar'id Y I VE!u are o; ground byloor'rdensers I-CliG' and ECH 'l V passe ssing cor'dnsersfICBll VVand* 1G85 are` also chd into the circu" but areswitched zout rcuitin the range ofhigherf'requenci'es. That i condensers I-Cj'land ICdjwill -serve i'S toigiye sufficient ley-passing tofground jat the p higher frequencies sincefthese condensersjmay l 'Over the' 'entire range of frequencies, Y however, i neutif'a-lizingfcnd'ensers` V I-CtiS and ICES', which may-consist of sectionsl of copper strapadjacent 'the-Aanodes; Yare also employed.' |Ihat is, these neutralizing'fcondensers are ernploye'din'V additinlto thesereen grids and'their by-passing circi-iitsVv toi' ground.- over! thev entire operatingrange 'ofJf-reque'ncies. The-use of such vncutralizing cir-- cuits i'nadditionlto'the screening circuits insures freedom 'zfrcr'nf 'spurious voscillations.4 and similar -eiect's.-r r Y' j :Coupling frrii'tiie driver stage, including tubes IN/"Ia'ndIlVIB, 'to the? final'power amplifier stage cornprisin'gfwater' cooledtubes `IV?!4 and IVIIL. is accomplish'ed.itlorugh` capacitors ICIIliJ, i648, {C102} nI'C'I)3,\IC49-ari'd IC'I05; t i 'The cond'ensers ICI'IlIi7 ICM-and.4 I'C |02 are equal sinlii'falue,` respectively, tocondensers ICII33, i049,- -'and i I CI 052 Y'Ihei Values'Vv of` the upper-"three ca- Y so: niet tric?cciipiiiigcap'acitiesfoni bein si'd'eslof s115 fiiniitingswitch uncut, circuit to; n y

stage yand Voutv mpliiiedA output 4*of theidriverfstage vconsisting of C81 v'and fICI'GBj The condensers are I "range-'lof lower frequencies,additionaliby- Y 4` the plate coil ILIB are equal.

voltage will be applied Vto the grids of the nal power amplifier tubes for different operating conditions. f

From the foregoing, it will be observed that deriser divider; Hence',`as'"`long a'sdilie= radio fre- Y quency plate voltage of the driverrstage' is held constant, the condenser divider serves to mainofY IV9v andIV fiiloverra very wide frequency range. By. virI-,ue'offth'ey condenser divider tuning, the driver'outputVY ys'tag'c'can beA adjusted over the entire freque'c'y'raige without affecting the ratio niegacycles can be covered withthree com-binations `rof thecondesersj Vin Vthjefvoltagedivider byme'ans of the tapsf'on coilV III-TIE" andi'bych'angf.

ing the position and :coupling of -a short-circuited iRmcA. As indicatcdycaeof "the iai-,ter is conriected-n series Vwith thel-'grdo'f tube LV?) fand 'Ivmjo'f the power amprer. y maestrias-'chores 151450' 4and inscri and radio frequency 'by-passjconde'nser lciatrhaveibeen K provided inv tlfiegrid circuit of thepower' arnpli-V y after, areprovided. for the power amplifier. Itubes -IzVQ Yandflfill'..k :'Also', vasi-will 'be describedmore fully-' h'ereinafter, theitankcircuit of the power amplifier comprises" the'V inductance IL5I', tuning condenser I CI I 2'; short-circuitin'gl strap.SB, con- Y .-byepassng condenser ICI'Z-and be; described moreifully hereinafter; comprises Athe inductor-11152,` tuningcondenser'ICI I4 and fixed con'de'nse'ers` 'IC-I I 5' tot IC I 22a inclusive'.` Motori-driven; adjustment or tuning ofr various put circuit are provided; Thus; 'greversiblez electrifc` motorj lAgdrives, neutralizing condensers .i Y

IGI-0B andICrlf'l. Directiongof-g'rotation is conf- 60 trolled byV switchY I-S'I. Limiting-switches dia- IAM. 1n# other v'vo-rdVs'-,V motor-'IAiZIlj simultanen ne missiles 111A;

n this way, proper' I the input capacity of the powerv amplifier tubes .Imi-arid I.V,I;forrn thev lwrvoltagefllegs of a`con-V tainja'A correspondingly constant excitation volt- Y age to the power amplifier across the power tubes of driver plateftopower amplifier grid radio fre- Y quency voltage. Actually some fixed adjustment of ,theV coupling capacitors ofthevoltage dividerV Y arrangement'may, be required." We have found thatY the enti-'re'- range from -sixtotwenty-two the other 'in series with theg'rid fof theothertube Also,-Y it' will be` heentire range `of Y,

Y from and lleida; f which will 'be describedin greater detail l-ierein-n 'elements :in the power amplifier :stage and out:`

gramatically inditdf et' *,ILSI 2': and LS1! 3;, limit fr' 'Y the amount of-,rotationgo-ffthe-motor in either 'is 'ineffeci la voitmeter, inegccitage Jor de- IISISQISZIJ and ISAZI, and indicators IMIS, IMIII, 'IMIS 'and- IMI'Il are provided for adjusting and indicating the' adjustmentI of `condensers ICI I2, coupling between inductors IL5I-'an'd IL52-and condenser ICI 4. Supply voltage for the` tuning indicating system is derived' from the rectifier arrangement IASB. Motor driving power is furnished through leads'IB and 2A. The power supply to these leads may be, for example, 220 volts 60. cycles A. C. current.

The limit switches, such as" ISIZ and ISI3, may'. be operated by cams, in turn operated or driven by reduction gearing coupled to the motor IA20, so that after a given numberof revolutions in one direction, limit switch ISI2 will be opened and after a given number of revolutions in the other direction limit switch ISI3 will be opened. Similarly, the potentiometer and tap arrangement |R43 and 40B may be controlled by reduction gearing also coupled to the motor IA29, the tap being in contact with and moved )Over a circularly. shaped potentiometer, Similar comments arev applicable to the other limit switches and potentiometers controlling the tuning indicators T|, The latter are provided with by-passing condensers |C`|5 to |C'|9 inclusive.

A preferred electrical and mechanical arrangement of the various parts of the power amplifier system and output circuit are shown in Fig- -ures 2 to 8 inclusive. One vfeature of the arrangement consists in an assembly wherein the coupling of the output circuits comprising IL52 with the preceding circuit comprising |L5I may be varied without varying the tuningY of the output circuit and wherein the tuning of the output circuit may be varied without changes in coupling.

As brieflystated before, Figure 2 is a side elevational, view f the'power amplier assembly comprising tubes |V9 and IVI 9; Figure 3v is a front elevational View of Figure: 2; Figure 4 is a sectional view of Figure 2; and Figures 5, 6, '7 and 8 illustrate arrangements and'adjustments for the power amplifiel` tank circuit comprising IL5| for different frequency ranges.

Turning to Figure 3, radio frequency excitation from the driver stage is fed to the grids of the power amplier tubes IV9 and IVIO at the grid input terminals 33, 83 and 33', 83. Two `leads, to each grid are provi-ded which are connected together and to external circuits at 54 and'54.

The neutralizing condensers ICIG'I and I CIIJB of. Figure 1 are illustrated in Figures 2 and 3 and `are seen. to comprise rounded or rectangular plates 56 directly attached to the tube anodes by means of brackets 56A and 56B. The variable plates of the neutralizing condensers are plates 59, 6|) each of which is of U-shape, so as to partially surround each of tubes V9 and VID. These U-shaped plates 59, 60, fixed together by insulating strip 59A, are simultaneously rotated on hinges 64, 64A by the operation of the motor IA2IJ. This follows since rotation of motor IA20 is translated into movement of condenser plates 59 and 6U by means of drum DI, cable 91 and vinsulating supporting anchors 63, 63A appropriately attached to the plate 59, 60.

Individual adjustment of the neutralizing condensers may be made by adjustment of the wing nuts (not shown) at points 54, whereby the condenser plates 56 may each be independently adjusted with respect to the simultaneously moved condenser plates 59, 60, This can be done since the brackets 56A and 56B are slotted s'o-that the. condenser plates 56 may be moved laxially along and fastened in aydesired position with respect to the vacuum tubes V9 and :VIII and, of course, with respect to the movable condenserplate combination 59,60. The tank circuit condenser ICI|2v of Figure 1 'is'alsoillustrated in Figures 2 and 3. This con'- `motor casing and bracket cam and slotted apparatus. The cam and slot apparatus is shown more clearly in Figure 2 at36 and 31.

Cooling water is fed to the anodes of the vacuum tubes through the insulating coils 24, 25 which provide for direct current insulation from ground. The cooling water is also fed and removed through the straight sections of insulating pipe 20 and 2|. AThe latter offer high impedanceto and effectively insulate the tube plates from ground for radio frequency currents.

As shown in Figures 2, 4, and 8 the inductive portion |L5I of the tunable tank circuit of Figure 1 consists of metallic tubing 339, 34D and 34|. This tubing 339, 349 and 34| is removably `xed vto the anodes by means of the wing nut operated flanges 5|.

Also, the inductor |L5I of Figure 1 may include for certain frequency ranges portionsof the vertically movable inductors 325, 325A of `Figures 2 and 4. This movable inductor portion 325, 325A is supported by stand-01T insulators |46 upon an edge-rounded rectangular metallic` plate 32| which is fed with plate voltage through conductive strap v|83(Fig. 2). Metal plate 32| in turn is'insulatingly supported from a grounded metallic plate 3I5 by means of additional stand-off insulators 3|6. y

Grounded plate 3I5 has attached thereto threaded spindles` 3|9 cooperating with internally threaded sprockets 3| 3, in turn supported by grounded metallic pedestals 3H). Motor I AZI drives suitable gear reducing `mechanism within the motor casing and the latter through bevel gear mechanism BGM and sprocket S drives chain 326. Chain 326 causes simultaneous operation of all ofthe sprockets 3| 3, resulting in movement of the entire assembly upwardly or downwardly. This assembly includes'ground plate 3I5, anode or B voltage plate 32|, and the apparatus supported by rectangular plate 32| which apparatus includes inductor 325, condenser I C|23 and choke coil IL56. The direction of rotationof motor IA2| and, hence, the direction of movement of the assembly depends upon the position to which switch ISB of Figure 1 is thrown. Movement of the assembly changes the inductance between the bottom turn 325, 325A and the upper turn 33,9, 340 which is fixed in position and clamped as illustrated at 5| to the anodes of vacuum tubes V9 and VID. In this way, .the total tank inductance is changed, decreasing as the assembly is lowered and increasing as it is raised and the turns 339,` 340 and 325, 325A brought closer together. This change in inductance gives one control on the tuning on the tank circuitcomprising IL5I of Figure 1. Another lcont-rol 'on prad-justmentbf this ,tuning haslaly Vready been mentioned. namely, .adjustment of and reversiblemotor 1|A23.

.Abetterunde'rstan'ding of .the manner in which the plate tank vcircuit'fincluctance',may be :varied Vmay be shad by referringrto Figures 5,6, 7 and v8,

which :diagrammatically .illustrate connections VAand adjustments .forvvarious frequency bands. i Y.

.Aszshown'in Figure, ,the upper tank conductors 339, 34D are fixed in position ,andconnected at itheirright handterminals, as indicated diagram-` .matically, to the anodes of tubes lVS vand 5|V|0. They are insulatingly supported by :the insulating supports 51,5113, ,as also illustrated in Figure 4. Also, as shownin Figure 5,.the plate 32|, corresponding `to plate 32| of Figure '2,.supports the stand-oil insulators |156, inductors 325, 325A, con- .denser 1C |`23,'and choke Vcoil .|L56. Choke lcoil m55-and condenser ICI23 are movable within the guide 323 along the plate 32| and in rthis lWay can have one of their terminals connected to vthe adjustable short circuiting bar SB. The inductance |LI of Figure 1, as illustrated in Figure .5, consequently maybe traced from the 'plateoftube IV9 through conductor 339,.the right "hand flexible connector '34B tothe right along .conductor 325A, across vmetal bar SB electrically connected to and slidable along conductors 325 and 325A, then along inductor .325 to the left, 'throughrthe left .hand lflexible strap 355 and then valong conductor34n 'to the plate of tube IVM).

iThe'upperplateSSt of condenser|C|23 of Figures v2r and l5 is connected by strap 387 to the shortcircuitingbar SB. The .choke ILES is ,con-` :nected to the short circuiting bar SB by strap 333 =of"-Figures 2 and 5. The lower plate of con-y denser |C|23 rests upon vand .is thereby directly vvconnected to'plate 32|. The capacityoflCl2'3 may be adjusted by moving the Wing nuty and pole arrangement supportingthe uppercondenser plate'386.

' As shown inlFigure 5, the lnductance of the Y tank circuit of 'the power amplifier stage conlsists effectively of two turna-in which the bottom 'turn 325, '325A is moved relative tothe fixed top turn 339, r3150, This inductive system yhas beenl 'found :useful 'for 'the range :of frequencies running 'from 6.0 to approximately 98 megacycles. Obviously, for various frequencies within this range'the Vposition ofthe 'short circuiting bar on theinductors 325, -325A'is changed and the sepalration of the turns 339, 3,40 and 1325, 325A'may vbe adjusted asbeforedescribed.- l

For Vthe frequency range runninggfrom 9.8 .to 10.5 megacycles, the `general arrangement of the "parts and adjustments are 'illustrated *in Figure `6. vFor this 'range the :snorting Vbar SB is moved -to the .extreme left hand end of the lower in- /ductors 325, 3125A.

For a frequency lrange of Vfrom -l0;-5 to 13.8 megacycles, the lower inductance bars are not used at all, the straps 345 inthat ,eventbeing connected, as illustrated 2in Figuref', to only the lupperV 'inductors 339, 3153 Yand "to 'the condenser |Cl23. The `choke m in this -casehas :one fof "its terminals connected through strap .333 'to the 'snorting' bar.SB, as shown,` .For still'higl'er'frefquenci'es, namely, v*for example, for arrange of Lfrequencies running "from 113.8 fto .222 \mega'cycles,

,8 n .the iarraneementcis ,shown 58,. In that case, fthe ,lower inductors 325 and ,'32 5A .are Ldisconnectedzffmrn :circuitand the-upper rinductol'. system previously. used is replaced-.Joy

Iinductors' 34| having a `'llfrger lconductor :dia-m.- veter than lthe rpreviously vemployed pipes ,or tubes .si-3am, y v Y vlieferring to Figure V2,1it -Willbe Y'found :the

.condenser plate arrangement 3|5, 32| ,improves stability and tends to lessen :the setting21110.y `.0f

parasitic oscillations. Ther plate voltage lead |83 isfggrounded for radio1frequencycurrentsfby means Yof .the condenser iQ-|24, as, illustrated .more clearly in liiguire 22. c

, The inductance Vlof .the output'circut |L52 vof ,Figure 1 consistsof a portion of the :hairpin in-v ductor L52 orLLEZA ofFiguresfl .and'2. h.The coil of the larger conductor size L52Aiis employed-for the `higher frequency range fsuclfry as, vfor example,

Cuit. 'Iheiiixed condenser tanks. |C||5 '.tof|;Cf|.22 K inclusive of Figure 1 are similarly illustrated in Figures 2 and 4. y

The variabley plates of :condenser Figure lare illustrated in Figure 4 at'3| and 310A, each consisting'of .a substantially rectan` .gular metallic plate having rounded Vcorners'.and

rounded Ledges. AThesemovable condenser plates Vare provided with ,metallic dishpan vsupports :i314 in turn supporting `stand-off :insulators SBS-.exi-

tending through-rounded .off perforations through vthe movable plates'. 310 and 313A'. In .this v.v'vay electric stress on the ,stand-oizinsulators' isre duced rWhile at :the same :time permitting the ,movable plates 370' and 310A rto beibrought closer to-thegroundedplate.358. "Rectangulargrounded 'plate 358 .extends across vand is thereby capacitively coupled to both Vof themovabletplates .'311'0 and 310A; '.Thisais clearfrom an A,inspection of Figure 4. Y

Referring again to Figure 2,.by means` of :motor .|,A25anditsreducing gearing driving the sprocket SPI, v.chain V325A and the remainingtsprockets SP2, SP3, SP4, ,SP5 ,and SP5, fthe latter three.

being 'directly behind SPL SP2;` and-SP3, condenser. plates3|5 andiSTBA areadjustedina vertical direction. The sprockets are supported upon ,the pedestals V365which in `turnare fastened to the condenser Y'plate 353. J'The lsprockets are. in-

lternally threadedzand the 'threads thereof fengage .the v'threads on 'the spindles .361, 368,:and 368A it-hereby .causing .movement 'of' vthe .movable .plates 33.0 and 31 A With-'respect tothe common condenser .plate :358 inla `direction perpendicular to the.planesoftlie.condenser plates. Fromwhat has been said'it should .beclearfth'at the spindle, sprocket -andmotor mechanism .|A25, SPI, i368, etc., is similar to thespindle chain and sprocket driving ymechanism Adescribed for .moving theV plates '315, 4325| and the apparatus supported thereby.

In a Asimilar Way motor .IAM .operatesythe sprocket, chain .and .spindle mechanism 313B,

321B, 353B, 353B andliA .whereby .the-.entire assembly of i-riductor` unitV |1352 and 'condenser |C| [A is moved -in'ra vertical'zdirection; "Hence,

operation of motorl .m25controlstheituning Iof the .output .circuit .independently of the coupling `to the tankcircuit, and operation of gmotorflAZll lmaybe usedtocontrol the coupling of themat- -put circuit .tothe ,platecircuitofg the power fampliasillustratedin'. Figure Y er without altering the tuning of ythev output circuit vcomprising I CII4. It is to 'be notedthat movement'oi the output assembly also includes condenser ICI I up to and including ICI22.

The output from the output circuit is taken through flexible conducting straps 38| and 38IA to suitable terminals supported upon insulators 385. From the latter terminal a conductive strap CS3 brings the amplified high frequency waves to suitable insulatingly supported output terminals 35| and 35IA as shown in both Figures 2 and 4. As explained in lconnection with Figure l, the various electric motorsare mechanically coupled by reduction gearing and other mechanical instrumentalities to change tuning of condensers, coupling, etc. "Also,v additional gearing is provided whereby each motor mechanically drives the movable armof a potentiometer which may be arranged in the form-of acircle. For example, as shown in Figurel, motor IA2I drives rheostat arm 4IB of potentiometer IR44. The potentiometer arrangement is illustrated somewhat schematically to the left of motor IA2I in Figure 2 at point IRM. Similarly, for example, the potentiometer associated with motor IA24 is illustrated at IR45 in the upper part of Figure 2 and the potentiometer associated with electric motor IA25 is illustrated at I R41, also in Figure 2.

Other parts of the apparatus illustrated in Figures 2, 3 and 4 should be self-evident to those skilled in the art, for example, the steel framework of the system and filament transformers T26 and T2l, blower motor AIB (Fig. 3-top), filament by-passing condensers ICI |18, ICI $9, etc., and ICI 25 of Figure 1. Also, it is to be noted that the grid chokes IL50 and IL59A of Figure 1 are illustrated in Figure 3, as is also condenser ICI3I). The stand-01T insulators with corona shields 9 for the tube sockets I0 and II are illustrated at 8 in Figure 2.

Having thus described our invention, what we claim is:

l. A variable inductor arrangement comprising a pair of conductors mounted in relatively fixed position, another pair of conductors insulatingly mounted upon a metal plate, connections connecting said conductors serially` together, and apparatus for moving said plate and said insulatingly supported conductors with respect to said fixed conductors whereby the inductance of the serially connected arrangement may be varied.

2. High frequency apparatus comprising a metallic plate, a ,pair of substantially linear conductors insulatingly supported upon said plate, an adjustable short-circuiting bar connected across said conductors, a condenser having one terminal connected to said short-circuiting bar and another terminal to said plate, a high frequency choke having one terminal connected to said bar and its other terminal to said plate, said choke and condenser being movable along said plate as said short-circuiting bar is moved along said conductors, a circuit for maintaining said plate at positive potential with respect to ground, a by-passing condenser connected between said plate and ground for maintaining said plate at ground radio frequency potential, another pair of substantially linear conductors arranged substantially parallel to said insulatingly supported linear conductors, connections I for serially connecting together all of said conductors, and apparatus for moving said plate with respect to said fixed conductors in order to effectively vary the inductance of 'said serially connected conductors.

' 3. In a high .frequency system,- a-pair of vacuum tubes each having an an'od'e, a pair -of linear conductors connected to said anodes, said'anodes and linear conductors being supported in rela'- tively fixed position, a second-pair of linear ncon'- ductors arranged paralleltofsaid `first pair, fiie'xible` connections between said conductors'fsaid second pair of linear conductors being 'insulatinglyv supported upon a 'substantially rectangular; metallic plate,l a 'short-circuiting. bar movablel along and electrically connected to said-pair of insulatingly supported conductors, a'lcodenser. connecting said short-circuiting bar toi-said metallic plate, a radio frequency choke coil connecting said metallicb'ar to said plate, a source of direct current voltage connected-to saidplate' whereby direct current voltage 4is `fed` fromusaid source to said plate and through said chokecoil, short-circuiting y-bar, linear conductors,` andthe flexible connections therefor to` said anode'syandl a lay-passing condenser'connected between said metallic plate and ground for maintaining said plate at substantially ground radio frequency potential.

4. Apparatus as claimed in claim 3, characterized by the provision of mechanical apparatus driven by a reversible electrical motor for moving said plate and the conductors insulatingly supported thereon closer to and further away from said conductors which are relatively fixed in position, whereby the inductance of the circuit connected between said anodes may be varied.

5. In combination, a U shaped inductor, means for feeding high frequency energy thereto, a second U shaped inductor arranged parallel to the first, an output circuit connected to said second U shaped inductor, said second U shaped inductor being arranged so that the plane of its conductors is substantially parallel `to the plane of the conductors of the first mentioned inductor, and mechanical apparatus under` the control of a reversible electrical motor for producing relative movement of said inductors in a direction perpendicular tothe planes of the conductors of said inductors.

6. High frequency apparatus comprising a looped conductor forming an inductance and a high frequency circuit coupled thereto, said circuit comprising another looped conductor forming an inductance, and a plurality of condensers electrically connected thereto, apparatus for adjusting the inductive coupling of said loops without substantially affecting the tuning of said circuit, and apparatus for adjusting the tuning of said circuit without substantially airecting the coupling between said looped conductors.

7. High frequency apparatus comprising a first looped conductor forming a first inductance, a second looped conductor forming a second inductance and arranged substantially parallel to the first, a grounded metallic plate of substantially rectangular shape upon which said second looped conductor is insulatingly mounted, a pair of condenser plates connected to opposite sides of said second mentioned conductor loop and being adjustably supported between said loop and said metallic plate, means for moving said oppositely connected condenser plates physically with reference to said grounded condenser plate, and means for moving said ground plate, movable plates and second conductor loop as a unit with respect to said iirst mentioned conductor loop.

8. Apparatus as claimed in claim '7, characterized by the fact that said movable condenser plates are moved by means of mechanical appamoon said rectangular grounded metal plate, said movable plates Vbengrmounted' between said ine ciuctorfandv said grounded plate `and being con'- nectedfto opposite sides of said inductor. v

: 10. High frequency apparatus comprising an extensive metallic plate, a high frequency choke 2&12531@ coil. insulatingly supported uponsaid plate; a di*` recti` current circuit' connectedftc said plate 'for maintaining said plate at ahigh direct current voltage with respect to ground, means' connecting one terminal of said choke to said pla-te'land its .other .terminal to high frequency apparatusga condenser having one terminal connected to ground, and'means for connectingthe'vother termin-al of said condenser to said'plate foriniain'a taining the latter tential. l. or 11. ApparatusI as claimed in claim 10 characat ground radiov frequencyfp terized by the fact that said metallic plate'is sup ported by stand-off insulators upon a second me- -tallic plate arrangedsubstantially parallel to said rst mentioned plateywsaid I second mentioned platebeing electricallyconnected to ground: y

THOMAS JAMES Y BOERNEBQ JOHNAW` sANBoRN.- Y

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