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July 23, 1946. 2,404,541 D. H. SLOAN' ' METHOD OF GENERATING HIGH FREQUENCY OSCILLA‘I‘IONSv Original Filed Nov. 4, 1940 10 Sheets-Sheet 1 ' 33 I //0 II _ 9 m lwogW)138 w M 5 & s/ o7 w 4 M; w m 9/4. 6 q??4550w:/60“ 7 3” uDa ‘ m Z w 55+79I ww Ji 1m A. Tvww H.A W. w .R50.NNAmm.E 5. R. v’ July 23, 1946. D. H. SLOAN 2,404,541 ' METHOD OF GENERATING‘HIGH FREQUENCY OSCILLATIONS Original Filed Nov. 4, 1940 10 Sheets-Sheet '2 j I IN VE/V TOP. DAV/D H. 5!. 0.4M. AT TOIPNEYS. July 23, 1946. D. H. SLOAN \ 2,404,541 METHOD OF GENERATING HIGH. FREQUENCY OSCILLATIONS Original Filed Nov. 4, 1940 ' 10 Sheets-Sheet 3 m7 INVENTOR'. DAV/D H. SLOAN. BY r K ;‘ ,l l ATTORNEYS. Ju?y 23, mag. D. H‘. SLOAN 24%,541 METHOD OF GENERATING HIGH FREQUENCY OSCILLATIONS Original Filed Nov. 4, 1.940 10 Sheets-Sheet 4 ./ . _ INVENTOR. DAV/D H. SLOAN.‘ I I3 +13 . £72)“ FM < ' Juiy 23, 194° D H, sLoAN 2,404,541 METHOD OF GENERATING HIGH FREQUENCY OSCILLATIONS Original Filed Nov. 4,v 1940 10 Sheets-Sheét 5 2; 5 INVENTOR. ' DAV/0 H. SLOAN. I BY ' . I f’ .0 "Aw AT TORNE YS. July 23, 1946. D. H. ISLOAN ‘ 2,404,541 METHOD OF GENERATING HIGH FREQUENCY OSCILLATIONS Original Filed Nov. 4, 1940 ‘ 10 Shee‘ts'-Sh_eet'6 £9.18. 2,47 ' l6 ‘ear, /7__ 2,21 / £32. __ we a‘ 3 _ v . Em £45 12.54 245 23' ‘12.25 .227 32.9 sear 1L9-- 527/47 320 5/0 2/2.‘ e50 INVENTOR. ' DAV/D H. SLOAN. MMQ A T TORNEVS. H Jy 23, 1946. 2,404,541 D. H. SLOAN METHOD OF GENERATING HIGH FREQUENCY OSCILLATIONS l0 Sheets—Sheet '7 Original Filed Nov. 4, ‘1940 a am P Ew a 1\§4 O56 6u/915 _/a 1%11”’1>1¢/ »,/._Max w ?r aans 5. Z wwZ/u , a E. w_.33 \.3 MJB ,4 L a0 5a4, .3 , \H\<R\X\ 93 455,,"W; A“;.aB 21V 4/m o\ m 2 N,. a w Hv 09. 3 /r D 79 7.. a M 9 5 V, Ava O) \ w m a. m x ._$7, . w m 4/ LcV Qm". 1S T N ATTORNEYS. . July 3, 1946. D. H. SLOAN 2944,54} METHOD OF GENERATING HIGH FREQUENCY OSCiLLATIONS Original Filed Nov. 4, 1940 a .395, 10 Shejets-Sheet 9 95‘~ as: _ / g I I / i / i , ’, 5731B ’ , 137a Q x. 'vh“ _ INVENTOR. DAV/D H. SLOAN. AT ZORNé'KS. July 23, 194%. D. H. SLOAN 2,4@4,41 METHOD OF GENERATING HIGH FREQUENCY OSCILLATIO‘NS Original Filed-Nov. ‘4, 1940 10 Sheets-Sheet 1o 'ilr 1 A 71.2 I’ 33/ »3a& INVENTOR. DA wo H. SLOAN. _ ‘k ATTORNEYS. Patented July 23, 1946 2,404,541 UNITED STATES PATENT OFFICE 2,404,541 METHOD OF GENERATING HIGH FREQUENCY OSCILLATIONS David H. Sloan, Berkeley, Calif., assignor to Re search Corporation, New York, N. Y., a corpo ration of New York Original application November 4, 1940, Serial No. 364,284. Divided and this application June 9, 1941, Serial No. 397,233 10 Claims. (01. 250—36) 1 2 This invention relates to electronic tubes, and particularly to tubes adapted for the production and modulation of ultra-high frequency oscilla relative radio-frequency resistance‘ of highlim- ~ tions, i. e., oscillations of frequencies of the order of 1,000 megacycles. This application is a di of control voltages; fourth, ?xed relationship be tween the various elements, irrespective of ‘tem perature or ordinary shock, so that the frequency‘ vision of my prior application Serial No. 364,284, ?led November 4, 1940. The progress of electronic and radio develop ment since the inception of the art has been marked by two steady advances. One of these ad vances has been toward higher power, the other toward higher frequencies. The latter line of ad vancement has been, to a certain extent at least, pedance, so that excessive energy will not be re quired to swing them through the necessary range > to which the device as a whole is tuned will not be ~ affected by relative changes of position; ?fth, ' minimum undesired or “incidental” radiation > from the various elements of the tube and its aux iliaries; sixth, a minimum of insulating material ‘ ' subjected to high-frequency ?elds. To these may be added the secondary requirements of demount_ ' incompatible with the ?rst, since with increasing ability for replacement of ?laments; facility in frequency the effect of interelectrode capacity has 15 water cooling and avoidance of hot spots, and case 7 become greater and more troublesome. Neverth less, up to the last few years, the diihculties have been met by a steady evolutionary process consist ing in large degree of re?nement in detail, which of tuning. From the conventional approach these require- 7 ments are incompatible to a large degree. A high‘ degree of control requires close spacing of cath has enabled the vacuum tube art to keep pace 20 ode and grid, which leads to high inter-electrode ' with the increasingly rigid demands of the manu capacity. Rigid structure ordinarily means mas; _ facturers and operators of transmitting and re sive structure, which again leads to high inter ceiving apparatus. electrode capacity. Water cooling systems tend to The attempt within recent years to carry the form effective antennae, leading to large "stray useful spectrum into the range of wavelengths in 25 power radiation. The broad'purpose of my inven the range of a meter and less has involved di?‘i tion is therefore to reconcile these and other ap culties of a new order of magnitude. parent incompatibles. For one thing, the frequencies involved are so high that the transit time of an electron stream across the interelectrode spaces of the tubes becomes an ap preciable fraction of a cycle. For another, even with connecting leads reduced to minimum lengths, their inductance has been su?icient so / Pursuant to this general purpose, among the objects of this invention are: To provide a' tube‘ 30 which is capable of producing many kilowatts of' power at extremely high frequencies; to produce ' a high frequency generator of great frequency stability; to produce a high frequency ampli?er‘ and oscillator tube of relatively high e?iciency, and particularly to produce such a tube wherein‘ that the capacities required in tuning them to the desired frequencies are small in comparison with the interelectrode capacities in conventional tum the losses due to undesired radiation from the ~ tube itself are reduced to negligible proportions; , structures and these capacities have therefore be come not merely a nuisance, limiting the efficiency to produce a high frequency oscillator and am of operation, but frequently an absolute bar to pli?er which may be tuned to operate at any de such operation; so much so, in fact, that it has 40 sired frequency throughout a reasonably‘ wide" range; to provide a high frequency oscillator and been only with tubes of very small size and conse quent small power output that operation has been ampli?er which may be constructed with thehigh' obtainable at all. degree of accuracy required to meet the close tol- ' erances demanded by the frequency of operation There therefore exists at the present time a need for a tube which will meet the severe re and to maintain those tolerances under the quirements of producing large power outputs by changes of temperature produced by such‘ opera- ' generation or ampli?cation at extremely high fre tion; to provide an electronic tube of the charac quencies. These requirements are ?rst, a cath ter described which may be fully ?uid cooled and ode-grid structure which will effectively modulate wherein the cooling system does. not introduce material parasitic radiation of radio-frequency an electron stream without the application of ex- ' cessive control voltages; second, a cathode-grid power; to provide a high power oscillator and am pli?er tube which is readily demountable: for re structure whose capacity and inductance rela tionships are so proportioned that they may be placement of ?laments; to provide means ofv den sity-modulating an electron stream at ultra-high tuned to the high operating frequencies desired; frequencies, in order to produce extremely short third, a structure lending itself to circuits of low 2,404,541 3 4 bursts of electron emission occurring at the peaks mounting the cathode in the region of sharpest of the oscillation and of substantially uniform velocity, whereby the conversion of energy into high frequency power occurs at high efficiency; to provide a-type of structure for high frequency electronic. tubes which. is of great ?exibility, and such a structure is to form the grid of pairs of cylindrical surfaces whose axes are parallel to the plane of the anode, and to make the cathode as. a ?lament or strip having a flat or slightly curvature. One of the best ways of obtaining concave face lying between the cylindrical sur faces of the grid. This results in the lines of force from accelerator or anode normally termi nating in the grid structure, none of them reach and effective method of tuning apparatus of‘the ing' the cathode, from which emission is there character described; and to provide a type of elec fore normally suppressed. A few volts relative trode support for high frequency electronic de change. in. potential. of the cathode, as referred vices which is massive and rugged; andwhich, at to either accelerator‘ or control grid, results in the same time, does not introduce interelectrode capacities which either severely limit. the fre 15 some of the lines of force from the accelerator terminating in the cathode surface, which is quencies upon which the deviceis operative or the accordingly subjected to an extremely powerful power which may be developed at such frequen field causing very large emission to the anode. cies. The result is what may be termed an “explosive” My invention possesses numerous other'obje'cts type of emission, giving electron bursts of high and features of advantage, some of which, to density for very short. periods. at the peaks of gether- with theforegoing, will be set forth in the the cycles. It will be evident that this structure following‘ description. of. speci?c apparatus em. results ina relatively high capacity as between bodying‘ and utilizing my novel. method. It is cathode and. grid, but the tuned transmission: therefore to be understood that‘my method is ap plicable to other apparatus, and that 1. do not 25 line support enables this capacity to be effectively resonated with an inductance as smallas may be limit myself, in any way, to the apparatus of the desired and still form a sharply tuned, high‘ Q present application, as I may adopt various other circuit whose high resonant input impedance may apparatus embodiments, utilizing the method, appear as resistive, capacitive or inductive as the within the scope of the appended claims. conditions of operation may require. The tube of my invention involves two basic Referring to the drawings: concepts. The first of these. comprises forming Fig. 1 is a longitudinalsection through a high electrode supports of‘ sturdy coaxial metallic cyl frequency oscillator tube. embodying my inven indersiwhich constitute a radio-frequency trans tion, the particular tube. illustrated employing a mission line of at least one and preferably a plu which will, because of such ?exibility, permit the construction of tubes exactly adapted to a large variety of powers and services; to provide a novel rality of quarter wave-length electrical links, with impedance irregularities at or near certain of the quarter wave points, the electrodes themselves forming a portion of these transmission. lines as considered‘ electrically. Means are preferably provided‘ for varying the‘ position of the imped .. radial arrangement of. ?laments and grids. Fig. 2 is a transverse section of the tube of Fig. 1, showing the-multiple coaxialgrid-?lament sup ports, and water connections for cooling the ?la ment mounting, the plane of section being on the 40 line 2—-2 of Fig. 1. Fig. 3 is a transverse sectionthroughthe anode structure of the tube, the plane of section being indicated by the line 3-3 of Fig. 1. Fig. 4 is an enlarged. detailed view illustrating teristic impedances of the quarter-wave sections water-cooling connections from the exterior of and their terminating impedan‘ces, it is‘possible 45 thetube to the ?lament mounting. to‘ make the: radio-frequency impedance of the Fig. 5 is a schematic sectional view through supports as viewed from the electrodes themselves ?laments, control grid, accelerating grid, bound extremely high, so that they overall effect. is- al ary grid, and anode of the tube. most: as though‘ the electrode capacities together Fig. 6 is a sectional view through the. grid with the: inductances required to resonate them ance irregularities to provide exact tuning; but this is not essential since, as will hereafter be shown, by a proper‘ combination of the charac were supported freely in‘ the- space‘within' an un broken metallic shield This latter feature is se cured‘ by providing multiple coaxial line sections support line, showing the radio-frequency by pass between accelerating and boundary grids and the tuning mechanismfor isolating. the con. forming'branch‘ pathsof greatly different imped trol grid and water cooling, the same. the’ grid opposed to‘ an anode or other accelerat ing' electrode in such manner as to produce an anode. Fig. 14 is a fragmentary section of'the- anode, Fig. '7 is. anenlarged detail showing the method an‘ce, certain of these paths acting as Icy-passes 55 of insulating certainof the. supporting. rings upon 0f negligible impedance at points where it is nec which the coaxial electrodeelements are carried. essary that some' circulating currents should flow, Fig. 8 is a section taken atrightlangles. to the although D.-C. insulation must be maintained, view- of Fig. l, andshowing the‘anode-supporting, whileat the same time maintaining the high‘ im pedance desired in other paths which would oth 60 cooling, and tuning system. Fig. 9- is a perspective View of the accelerator erwise lead to radiation. By placing these by grid. pass sections at current nodes, the FR losses Fig. 10 is an elevation of the control-grid-struc therein'may be made too small to‘need considera ture. tion. Fig. 11 is a sectional view, taken on the plane The second fundamental concept comprises 65 between the ?lament and grid structures, and mounting on the ends of such supports, prefer showing in detail the ?lament support. ably in biaxially symmetrical con?guration, one Fig. 12 is a‘ fragmentary axial‘. section taken on or a; plurality of cathode=grid combinations which the line l2—l2' of Fig. 1.1. act, as before stated, as thetermini of the trans Fig. 13‘ is anv elevation. of the active face of the mission lines formed by the supports; mounting 70 the plane of section being’ indicated by the‘line |a'_r4 in the preceding ?gure. in the immediate neighborhood of the grid‘; and 75 Fig‘. 15 is an. elevation of the boundary grid; electrostatic field between grid and accelerator which comprises‘ lines of force very sharply curved 2,404,541 5 6 Fig. 16 is a sectional view taken on the line internal recess or counterbore in an annular grid Iii-l6 of Fig. 15, and showing a portion of the anode in elevation. Fig. 17 is an elevation of one of the ?laments. Fig. 18 shows a modi?ed form of coaxial line structure for grid-?lament support in a tube gen erally similar to Fig. 1, but adapted for use either ?ange 3, clamping a boundary grid 4 between the as an ampli?er or an oscillator with inductive feed-back. Figs. 19, 20 and 21 are sectional views through the tube of Fig. 18, taken on the lines numbered in accordance with the ?gures. Fig. 22 is a longitudinal section through a tube built in accordance with this invention but where in a cylindrical, rather than a radial ?lament grid and anode arrangement is used. Figs. 23, 24 and 25 are transverse sections through the tube of Fig. 22, taken on the lines housing tube 2 and the ?ange 3. A rabbet on the outer periphery of the ?ange 3 receives one end of a main support cylinder 5, whose other end terminates in another annular ?ange ‘I. All of the parts thus far mentioned are of metal, and I have found it convenient to make the ?anges of steel, and the tube 5 also of seamless steel tubing, while the ‘cylinder 2 may be either chromium or copper plated steel or solid copper, with copper preferred since it forms a portion of a resonating circuit. Carrying on from the ?ange l is a glass or “Pyrex” cylinder 2 which abuts a terminal ?ange I0. ‘ . As has been mentioned already, the device as whole is fully demountable. The ends of the tubes ‘ contact the ?anges with smooth machine ?t's. The. joints thus formed are sealed by applying Figs. 26 and 2'7 are detailed views indicating‘ 20 thereto ordinary wide elastic .bands as indicated the tuning mechanism for the tube of Fig. 22. by the reference characters I I , these bands being indicated by the respective numerals. Fig. 28 is a longitudinal section on a larger smeared before-application with a small amount scale through the ?lament support of the tube of Fig. 22. of vacuum line stop-cock grease. Fig. 29 is a transverse section through the sup porting columns of the tube of Fig. 22, showing the construction of the centering mechanism, the plane of section being indicated by the line 29-—29 of Fig. 28. the structure thus far described with the excep- , as, in fact, are all of those herein described al type of structure here shown is that the ‘ability of ' ' ' It may be pointed out at this time that all or tion of the terminal ?ange It is at D.-C. ground potential, and as will later be shown in detail that ' ' the'entire exterior structure is substantially at radio-frequency ground. This means thatthe Fig. 30 is a sectional view taken on the line 30 insulating section ‘formed by the cylinder 91'is not 30-30 of Fig. 22. subjected to R.-F. ?elds. It also renders easy the Fig. 31 is a fragmentary section taken on the support of the device by any desired ‘external line 3l—3l of the preceding ?gure, showing the means, Part of such support may be the connec-'v passage of the cooling pipe past the anode and tion to the pump, which is by a pipe l2 of rela between the two sections of the ?lament support. 35 tively large interior diameter, welded or other Fig. 32 is an impedance diagram for an open wise secured'into the, bottom'of the anode hous-. ended, half-wave length section of transmission ing 2. This pipe is not ‘shown in Fig. 1, butis line. clearly visible at the bottom of Fig. 8. . In the ensuing speci?cation the invention will The various elements which contribute to the ?rst be described in its various aspects as applied 4:0 electronic action of the tube are mounted‘ within to an oscillator tube of moderate power (i. e., the envelope thus formed on columnar supports‘ approximately 10 kw. peak output at 20 to 40 each of which has transmission ‘line character- ' centimeters Wavelength). Following this there istics designed to meet its particular‘ function.‘ will be described two modi?cations illustrating These elements are shown in schematic arrange~' respectively the application of the principles of 45 ment in Fig. 5, and comprise an anode 13, a my invention to a similar tube adapted for am boundary grid 4, an accelerating grid £5, a con pli?cation or for generation of oscillations by trol grid l6,'and a ?lamentary cathode l1. _ inductive feed-back, and to a somewhat higher s Fig. 5 is drawn to a greatly enlarged scale and output device showing the principles as applied to shows a fragmentary section of the'elements 00 a tube constructed with cylindrical rather than 50 operating with a single ?lamentary cathode. ‘ In radial arrangement of electrodes. the tube here shown'six such cathodes are used The tube shown in longitudinal section in Fig. and the portions shown of the other elements are” 1 is of the demountable, constantly pumped type, repeated for each cathode. One advantage of the ‘ though the principles involved are not limited for 55 the tube to supply power output varies almost' " use in such tubes. From the structural point of directly as the number of ?laments used, and that view the tube comprises a series of ?anges con the changes required to add additional filaments nected by sections of tubing and held together in are relatively minor. ‘Tubes have been designed compression. From a practical point of view it conforming substantially to the structure here is advantageous to have the ?anges pierced for 60 shown with as high as twenty-four ?laments, and held by circumferential bolts to hold the each with its attendant grid-anode structure, but parts ?rmly in position when the tube is not un since each of these assemblies is merely the dupli der vacuum, but when in use the external air cate of the others as far as performance'is con,~ pressure tends to hold the entire device together, cerned it'is 'su?icient for the present to consider . and the tube has actually been operated without one only. Considering, therefore, the 'portio-n'of the ele-.' the retaining bolts, these have therefore been omitted in the drawings since they add a further ments shown in Fig. 5, the anode i3, preferably 1 complexity of detail to an already complex struc ture. operated at the maximum potential'of the system,‘ made of high conductivity oxygen-free copper, is: Considering for the moment, therefore, only 70 say 10 to 50 thousand volts positive. It is pro the external structure which forms the housing and which supports the remainder of the equip ment, the tube comprises an anode housing ?ange I which is grooved to receive tightly the end of a tubular anode housing 2. This housing ?ts an - vided with a V-shaped- groove 20 with'its axis‘ parallel to the axis of the ?lament.‘ Next; pro‘ ' ceeding toward the ?lament, is the boundary grid 4, which is also preferably made of oxygen-free ‘ copper. This is provided withan aperturelsur 2,404,541 ? 8 rounded by a collar 2| in accurate alinement with the groove 23 in the anode. Next in line is the accelerator grid It, with an aperture 22 which grid is so adjusted that emission can occur only for an instant at the cycle peaks, and cut-off may occur even before the ?rst electrons emitted have traversed the space charge region. Fur thermore, While in this region there is a maxi mum difference of velocity as between electrons, is somewhat narrower than the opening in the boundary grid, and which is operated at a poten tial above the cathode of from 5 to 20 thousand volts. All potentials mentioned are illustrative and relative only, since the actual values used will depend upon the size, power output and op both by reason of differing initial velocities of emission and, more important, by reason of dif fering acceleration due both to phase of emission erating frequency of the device. Furthermore, 10 and ?eld strength at various parts of the cathode modi?cations in design are possible whereby the surface. The important point is that because the region functions of certain of the grids are combined, other electrodes are operated at ground potential, is so shallow all of the electrons emitted do get through it before the cycle has advanced too far, etc. Such modi?cations will be considered later; the purpose here is to show the application of the 15 and, having traversed it, fall into the region of high potential gradient where acceleration to~ principles of my invention to the present tube. ward the anode is very great; space charge ef The most important portion of the combina tion is the arrangement of the cathode-grid feet is of no further moment, and they receive so large a portion of their ?nal velocity that their structure. The important features here are ?rst, differences of velocity in the initial region are that the control-grid elements comprise parallel immaterial. cylindrical surfaces, curved as they are present— It should be realized that while space-charge ed to the ?lament. In the present case they are effect prevents some emission and decreases the acceleration of electrons emitted, it will not drive plate without affecting their performance. Be 25 those which have been emitted back to the cath ode nor prevent their reaching the anode. It tween these surfaces, and slightly back of the follows that the space-charge region may be con plane of their centers of curvature, lies the ?la rods or wires, but they could be cylindrical sur faces formed as the edges of a slot in a ?at ment, which has a ?at or preferably a slightly sidered as a reservoir for emitted electrons. With hollow ground face presented to the anode. It conventional grid-cathode structures it is rel is convenient to operate the ?lament at ground atively deep, so that, at the frequencies and potential (disregarding for the moment the slight powers at which this tube is intended to oper ate, transit therethrough occupies a major por voltage drop along the ?lament) and, for the powers here considered, to operate the grid [6 tion of the cycle, and with the varying velocities at 200 to 500 volts negative. obtaining while in this region the electrons It will be seen that at the orders of voltages 35 straggle through to reach the anode in such given the major ?elds are from the accelerator varying phases that the density modulation of grid 15 to the control grid. As is well known. the stream is almost if not entirely lost. the lines of force constituting such a ?eld termi With the arrangement of my invention, how nate at right angles to the surfaces of the ?eld ever, the space-charge region is so shallow that de?ning electrodes. It follows that in the region 40 even the stragglers among the emitted electrons adjacent the cathode the lines of force emerge traverse it in less than a quarter cycle and in from the grid wires in the general direction of stead of the density modulation of the electrons the cathode and then curve very sharply to being lost they reach the anode in bursts of such ward the anode in a direction nearly at right power and suddenness and with such close ve angles to their direction of emergence. There is locity grouping that I have termed cathode-grid also a fairly strong ?eld between the control combinations of this type “explosive.” The ob grid and the cathode itself, which is superim ject of the design is to make the electron reser posed locally upon the ?eld between the control voir constituted by the space-charge region as grid and accelerator grid, and is directed toward, shallow as possible, and in practice the ideal can instead of away from the cathode. As a result 60 be so far realized as to permit density modula of the interaction of these two ?elds none of the tion of electron streams at frequencies in the lines of force from the accelerator-grid normally terminate upon the surface of the cathode. Emission has therefore no tendency to leave the latter, since the space adjacent it is nearly neu tral, with such weak ?eld as exists therein di rected toward the cathode. As is the case with any grid-controlled tube range of 1,500 megacycles, where in the past it has been necessary to use velocity modulation, involving larger and more complicated struc tures, to get reasonably effective results, even in smaller sizes and at much lower powers than those here contemplated. When the tube here shown is used as an OS cillator in the manner now to be described, the positive some of the lines of force from the ac (50 various potentials are so arranged and propor celerator-grid which formerly terminated on the tioned that the transit time of the burst of elec control grid now terminate on the cathode, and trons is substantially one-half cycle. The anode as the cycle progresses the cathode-control grid I3 is in a tuned circuit, as is also the grid IS. ?eld weakens or even reverses, permitting emis The condition of oscillation then is that the po sion toward the anode, and a space charge builds tentials of the anode and the grid swing in the up in the region immediately in front of the same sense, so that the grid reaches its peak of cathode face which has the usual effect of lim positive potential at the same instant as does iting emission. The distinguishing feature here the anode. is that the region where the ?eld is weak enough One of the results of the conformation of the to permit such space charge effect is very shal~ electrostatic ?elds is a strong focusing action low, so that even with the low velocities impart upon the electron bursts, and these bursts accord ed to them by such relatively weak ?eld the elec ingly fall upon an extremely limited portion of trons can and do traverse it in a reasonably small the anode surface, substantially none reaching fraction of a cycle. either of the intermediate grids. The anode area operated through cut-off, when the grid swings The biasing potential between cathode and 76 upon which the electron bursts impinge is that 2,404,541 9 10 included in the V-shaped slot 20. The reason for this arrangement is to spread the area of impact At its upper end it is threaded to receive a grid- support ring 21, whichis clamped between locking nuts 29 and 30, and an additional locking screw and so increase the size and decrease the in tensity of maximum local heating, while increas ing the cross-sectional area of thermal conduc tivity by which cooling occurs, and also to insure that secondary electrons are not projected into regions of high ?eld intensity which would ac celerate them so that they, in turn, would cause serious heating effects. It has already been stated that the transit time of the electron burst is one-half cycle of oscilla tion, and it follows that immediately after the electron burst has occurred the anode has started 3| (Fig. 10) is also provided for further security. The pairs of parallel grid wires I6 project from the ring 21 parallel to its radii, six pairs of grid wires being provided in the present‘design, the pairs being equidistantly spaced around the periphery of the ring. 10 , , Two sliders are mounted on the column 25. The upper slider 28 comprises'a short section of tubing 32 surfaced to a sliding ?t on the column 25 and shouldered at each end to receive discs‘33 and‘ 34 between which a short section of tubing The electrons accordingly 15 35 is clamped. The column 25 is provided in this to swing negative. reach their maximumgvelocity at or about the region with a longitudinal slot for the passage plane of the accelerator grid-ideally, just as they pass the effective plane of the boundary grid 4. As the anode continues to swing negative they of a-screw 31’ which engages a piece of tubing In passing through this decelerating ?eld the by sliding the rod 4|. 39 sliding within the column. The tubing 35 ter minates in an annular block 40, and an adjusting encounter a decelerating ?eld, either in an abso 20 rod 4| is threaded into one side of the block and lute sense or, if still being accelerated by the passes to the exterior of the tube through a gland D.-C. ?eld, from the anode, at least in compari box ‘42 and a “Wilson seal” 43. It is apparent 'son to the acceleration of the D.-C. ?eld alone. that the position of the slider may be adjusted , ~~ electrons are delivering energy to the anode cir 25 A word. as to the Wilson seal may here be in cuit, and they are traveling at minimum relative order, and in this connection attention is drawn velocity when they enter the slot 20. This slot to the showing at thelower right of Fig. 8. The acts in some degree as a Faraday space, and the seal proper consists of a normally ?at washer 45 electrons su?er little change in velocity or energy of synthetic or natural rubber, which is forcedv as they pass through it. Therefore their Work 30 against a conical seat 41 by the internally conical is done and their transit time effectively over as edges of a gland 49. When the washer is un soon as they have entered it. stressed the aperture therethrough is slightly too Since the acceleration of the entire burst of small for the rod 5|! which it is desired to seal. electrons takes place with substantial uniformity The seal is lubricated with a small quantity of they retain their close grouping at the time of 35 vacuum stop-cock grease. Such a seal is vacuum impact, and since the impact occurs when the tight under conditions where other known types electrons constituting the burst have suffered maximum deceleration there is a minimum of energy wasted as heat and the oscillator conse quently operates at relatively high e?ciency. of packing would leak badly, since the di?eren tial pressure on the washer serves to make it hug the central rod more tightly and it remains tight 40 whether the rod be subjected to rotary or sliding For operation in the manner described the motion in either direction. desiderata are that the control grid l6 and ?la Returning to the general tube structure, the ment ll should be e?ectively isolated from each second and lower slider 5| is essentially similar other both as regards D.-C‘. and radio-frequency in construction to that just described, except that 45 potentials, and should have an effective capacity its actuating rod 52 is mounted externally of the sufficiently low so that it may be tuned to the column 25 through’the gland box 42 and Wilson desired operating frequency, or, in other terms, seal 53. it must be capable of being connected in circuit The slider 5| makes a close sliding fit within with an inductance su?iciently small to tune to a cylindrical conductor 54 mounted in the ?ange that frequency. The accelerator grid I5 must be 50 I0 accurately concentric with the column 25 and insulated from the other elements to maintain maintained in this concentric relation both by its D.—C. voltage, but should be effectively ground the slider 5| itself and by an'auxiliary diaphragm ed as regards radio-frequency potentials. The or spacer 55. The tubing 54 does not extend the boundary grid 4 should also be grounded to radio full length of the central column, but terminates frequency and for convenience in operation and 55 a distance above the flange 1 which is somewhere safety’s sake should preferably also be grounded in the neighborhood of one-eighth of a wave as regards D.-C. potential, as it is electrically con length at the mean frequency for which the tube tinuous with the envelope. The anode should be is designed. _ ‘ ' free as regards both A.-C. and D.-C. potentials. Accurately coaxial with the column 25 and its 60 The various mounting and auxiliary means next surrounding conductor 5| is a third conducting . to be described are designed to meet the desid cylinder 51, mounted on the flange 1 and extend erata as fully as possible. In this description ing below it for approximately one-eighth wave-v terms such as “above” or “below” are used to length, so that the two conductors 54 and 51 over indicate position as shown in Fig. 1. They have lap by a distance approximately equal to one no other signi?cance, as the device may be op 65 quarter wavelength of the average operating fre erated in any position. quency of the device, wavelengths in this sense Starting at the bottom of Fig. l, with the flange being used to mean the wavelength of the fre I9, a high conductivity column or pipe 25 extends quency transmitted along the two tubes as a a major portion of the length of the entire device 70 coaxial transmission line. There is no metallic to the plane of the ?ange 3 and the boundary contact between the two conductors 54 and 51, grid ll, This column is brazed or otherwise per and they are separated by vacuum so that dielec manently secured into the ?ange in so as to be tric loss-does not occur in the space between accurately concentric with the remainder of the tube structure and, of course, to be vacuum tight. 76 Column 51 is brazed or otherwise secured in them. ' r ' 2,404,541 1i the flange 1, is made of highly conducting mate rial (preferably oxygen-free copper) and is pref erably provided with a cooling system comprising a water pipe (59 coiled around and soldered to the external surface of the column. The ends of this pipe are brought out through the ?ange ‘l at the right of Fig. 1. The upper end of the column 51 carries an intermediate ring 6! which supports indirectly one end of each of the ?laments IT. The other ends of these ?laments are carried by a group (here six) of pipes 62 mounted in the annular inter-space between the column 51 and the outer shell 5. The lower ends of the pipes 62 are mounted in a ring 63 which is bolted to and insu lated from the ?ange l as is shown in Figs. 2 and '7. The ring 63 is counterbored at three equidistant points to receive insulating beads 64 of porcelain, lava, or other refractory insulating material which beads space the rings slightly from the ?ange ‘I. A cap screw 65 passes in turn through a clamping cap 61, a second bead 69, the 12 is 50 mils. The grinding is preferably performed in a jig which deforms the wire slightly in the longitudinal direction, so that the ends‘of the ?lament are ground a few thousandths of an inch thinner than is the central portion. This grind ing forms the flat emitting surface of the‘ ?la ment, and if done with a relatively small wheel whose axis is maintained parallel to the length of the ?lament, it gives the slight hollow grinding which has already been stated to be advantageous. The effect of thinning the two ends, adjacent the point where the ?lament is clamped, is to give a greater current density at these points, with a consequent greater liberation of heat which com pensates for the heat conduction to the clamping means and results in substantially constant tem perature and substantially constant emission over the entire effective length of the ?lament. Being of pure tungsten, the ?lament retains a degree of resiliency even at its emitting temperature, and this, together with its resilient support, prevents buckling or change of plane of the emitting sur face when in operation and keeps the electrical rings 63 and the bead 54 to clamp the ring ?rmly constants of the device ?xed under such minor to the ?ange. It should be noted that the poten tials which this arrangement must withstand are 25 variations in operating temperature and expan sion, and inequality in these factors as between of low frequency and are only those across the the several ?laments, as inevitably occur in ?lament, i. e., the insulation need only be of suffi practice. cient value to withstand a few volts (three at 60 Cooling for the support of the inner ends of cycles in the instant structure) and the insulating material is not subject to dielectric heating from 30 the ?laments is accomplished by conduction through the support rings ‘M and BI to the col radio-frequency ?elds. umn 5'! and thence through the cooling coil 60. The actual ?lament mounting can best be seen Cooling for the outer supports is by circulatory in Figs. 11 and 12. Each of the tubes 62 carries system within the support pipes 62 themselves. an inwardly projecting L-shaped lug l0, and the inner ends of the lugs are provided with slots ‘H 35 A small water pipe 99 enters the side of each of the support pipes 62, and extends axially within for receiving the downturned ends of the staple it to a point adjacent the lug ‘HQ, 50 that water shaped ?laments ii, the ends being clamped into entering this pipe will be squirted against the place by set-screws '12. The inner ends of the inner end of the lug. From there it returns ?laments are clamped in an annular groove 13, through the pipe 62 externally of the pipe 90 to formed in an inner mounting ring 'i'li which is the bottom of pipe 62, where the end 90' of the supported on column 51 by the intermediate ring next pipe is connected to carry the water to the 6! before mentioned. The actual clamping of next ?lament support, circulation thereby occur the ?lament ends is accomplished by pairs of set ring through each of the support pipes 62 in screws 75 hearing on small blocks ‘H. 45 The pipes 62 are surrounded by open-ended The supply for this circulatory system is cylindrical conductors 79, which terminate at the through a ?tting designated by the general ref level of the upper end of the lug and extend down erence character 9!, comprising coaxial pipes 92 over the pipe 62 for approximately one-quarter and as which connect respectively to the two ends wavelength and are supported by the ring 6!. of the system. The outer of these pipes is perma Within the conductors 19 are inner tubular con nently secured to the support ring 63 (see Fig. 4) . ductors 6B of substantially the same length, open The ?tting 9! passes through the flange 1 and is at their upper ends and mounted by their lower insulated therefrom by insulating bushings 94 of ends on the pipes 62 by means of conductive steatite or other refractory between which is a blocks 8|. The concentric tubes 19 and 8B are both open at the ?lament end, being notched to 55 compressed rubber washer 95 forming a vacuum~ tight seal. A connecting lug 91 for connecting clear the lugs ‘is and also being provided with one ?lament supply lead is mounted upon the alined holes to permit tightening of the set-screws ?tting SI, and the ring 63, and the circulatory 72. It will thus be seen that the only connection system comprising pipes 90 and 62 all constitute between the inner column El with its supporting rings El and ‘M and the group of ?lament sup 60 the conducting systemfor supplying the ?lament current. The return circuit is through the col port tubes 82 is the ?laments themselves. succession. These are shown in Fig. 1'7, and as will be seen , _ umn 57 and the ?ange 1, to which a second con necting lug (not shown) is attached. are relatively short and rigid. They are prefer There are two other features comprised within ably of pure tungsten and have a considerable degree of strength. It will further be seen that 65 the ?lament-grid structure and their supporting systems. The ?rst of these is a sliding plug 99 the support afforded their outer ends by the tubes mounted in the end of the inner support column 52 and lugs ‘it is light and of small inertia and 25, and adjustable as to position by means of an that the tubes 62 have relatively large resiliency. operating rod H33, and an offset extension rod l?l The ?laments therefore are very unlikely to be passing through a Wilson seal I02 in the gland ruptured by shock on the device as a whole, and box 42. The second is a. cooling pipe H23 which there is ample ?exibility to take up their ex extends substantially the full length of the inner pansion. column 25 and is soldered thereto adjacent its Each ?lament is preferably formed of round upper end for better heat transfer. tungsten wire, one surface of which is ground We are now in a position to consider the elec ?at or slightly concave. The diameter here used 2,404,541 13 ~ trical characteristics of the ?lament-grid struc ture in view of the desiderata above set forth, and it is believed appropriate to do this at this point, since the same principles are involved in the supports for the remaining elements of the device and the explanation of all will be simpli?ed if these principles are in mind. The necessary 14 a‘ number of aspectsall depending on the general relationships above set forth, "but in the treat ment, here adopted they are generally considered as divided into sections of quarter-wave length, or thereabout, as'thisis believed to lead to the simplest explanations. I ‘ separation of the elements as regards D.-C. or low Weare interested in the impedance of the grid ?lament support line as viewed from the grid frequency potentials have already been accounted end, but ‘this, impedance is dependent upon the for. There is no metallic connection between the 10 terminating or output impedances of the various grid-support column 25 and the ?lament-support sections and, therefore, in order , to determine what the grid-end impedance will be, we must system comprising the column 51, and the sup port pipes 62. Remaining to be accounted for is consider the various elements, section by section, the impedance relationship between the grid and starting from the outermost or lower end of the ?lament members, and this is dependent upon 15 tube as shown in Fig. 1. c 7 7 From this aspect the ?rst section of the struc the impedance of the coaxial transmission line ture is. the section including the adjusting rods formed by the inner and outer columns 25 and 51 and the coaxial conductors associated therewith. 52, 4|’, etc., the ?ange I0, and the section of the The impedance characteristics of transmission tubular conductor 54 illustrated as below the end lines whose lengths are of the same order of mag 20 of the column 57. Electrically this portion of the nitude as the wavelengths of electrical oscillations structure is asingle conductor, and viewed from its upper end constitutes an end-fed antenna. transmitted thereby are now well known, but they It is preferable that its length be of the order are restated here for convenience in the explana of one-half wavelength at the operating frequency tions that follow. Most of them can be derived from the impedance diagram of a half-wave line of the device, in which case its effective imped ance Z2 will be in the neighborhood of 1,000 ohms. open at the output end, as shown in Fig.32, which If<its length be reduced to one-quarter-wave indicates such a line diagrammatically, and shows length its effective input impedance will likewise the approximate curve of relative impedance be reduced to the neighborhood of from 50 to 100 . looking into any portion of the line from the right, resistance of the conductors themselves 30 ohms, the quarter wavelength conditionbeing the least desirable in practice. This antenna is con being assumed to approach zero. Extremely sidered as being fed'by the coaxial transmission short sections show a high capacitive reactance, line comprising the tubular conductor 54 as the which falls to the characteristic impedance of inner element and the column 51 as the outer of the line at the 1/8 wavelength point, and to zero at the quarter-wave point, i. e., a quarter wave open-ended line acts as a dead short. From this point on the apparent reactance is inductive, rising again to the value element. With the spacing shown such a trans mission line will havea characteristic or surge impedance Zn of about 10 ohms, and as has already been stated the length of this section of trans mission line is approximately k 4 where A is the wavelength at the frequency of operation. If we consider the quarter-wave con at the % A point and approaching in?nity at 45 dition to be ful?lled exactly'the impedance look ing into the coaxial line’ from the grid end will be 1/2 A. ‘ The same diagram may be taken as represent ing the impedance of a shorted-end line if the origin be taken at the nodal or quarter-wave _Z_o2 ' point, which appears as a short when looking 50 If .the antenna section of the system have ‘an im-_ pedance of the order of 1,000 ohms, the character istic impedance of the line being 10 ohms, the ' into the line. For short sections the reactance is small and inductive, it rises to at the 1A; x point and approaches in?nity at A 4 Since this appears as an open circuit, increasing the length of the line repeats the portion of the‘ diagram shown at the left of the nodal point. Stated in another manner, a quarter-wave open line or a half-wave shorted line appears much like a series resonant circuit, while a quarter wave shorted line or a half-way open line appears like an anti-resonant or parallel resonant circuit. input impedance of the line will therefore be 11¢; of an ohm. This low impedance therefore be comes the closing impedance of the sectionmof line immediately preceding it. From one .point of vi'ew‘it acts as a radio-frequency by-pass be tween the inner conductor 54 and the outer con ductor 51, so that viewed from the input end, at radio-frequencies the cylinder 54 and outer column 51 appear as a single conductor, and form, in connection with inner column 25, a single radio-frequency transmission line considered as fed from the grid-?lament end through a slight impedanceiirregularity where the inner cylinder 54 terminates. Its effect from another point of view will be considered later. ' ‘ ' ‘ Even if the conditions as to impedance of an The only other relationship necessary to the understanding of the present invention is that tenna and length of the coaxial line constituting the column 51 and cylinder 54 are not exactly ' the characteristic impedance of a quarter-wave line is the geometric mean between its input and 70 met the result will be substantially the same. The antenna impedance can easily be kept above 100 closing impedances. The short-circuit and open ohms, making the impedance looking into the circuit conditions are, of course, merely special quarter wavelength line 1 ohm. If the "length: cases of this general relation. of the line section is not'exactly one-quarter The lines comprising the element supports of the tube of my invention may be considered from 76 wave,v butv is'still materially greater than ‘one 2,404,541 15 16 eighth wavelength, ‘the input impedance will still impedance to a ?nite value and introduce large losses through radiation and dielectric phenom be low in comparison with the characteristic im pedance of the line, and although more power ena. will escape than if optimum conditions are met The design problem to be met, therefore, is the the amount of power wasted by such undesired UL design of a structure which, when terminated by an impedance approaching in?nity, will have the radiation will be very small. properties of an anti-resonant circuit as viewed The section of the inner line comprising the from cathode and grid. This structure is pro cylinder 54 and column 25 terminates in the vided by two additional quarter-wave sections of slider 51, which, as it is of large area and makes good contact with both conductors, may be con 10 the same line, The ?rst of these sections extends to include sidered as of zero impedance. This section may the upper slider 28, and its design is such that be tuned to exactly one-quarter wave by moving its electrical length may be changed in opposite the slider. Due to the spacing between the two sense to its physical length; i. e., such that it conductors the characteristic impedance of this may be “?tted in” beneath the section above it section of transmission line is high, and if the even when the length of the upper section in resistance of the line were zero the input im creases with decreased frequency of operation or pedance would be in?nite. Actually it may always vice Versa. be made to exceed 100,000 ohms and under opti This effect is obtained by means of the ir mum conditions may reach ten times this value. This section therefore forms a tuned radio-fre 20 regularity introduced by the low-impedance line section constituted by the slider 28. From the quency choke of extremely high impedance inter posed betWeen the ?lament-grid structure and the outside world, and the impedance involved is so high that practically all energy reaching it is top of the high impedance section already de scribed to the slider is a length of relatively high impedance line of less than 1/4 wavelength which re?ected back to its source. 25 therefore appears as a capacity variable from zero to some small value as the slider is moved What actually happens can be expressed more nearly in the terms of low frequency power line transmission if we think of the antenna as a load to change its length from zero toward A which is fed by a line terminating immediately 4 above the top of the column 511, Current fed to 30 this line from the central column 25 must pro To this is connected the relatively great capacity ceed down the column, across the slider‘, and back of the slider portion of the line about 1/8 A in to the top of the conductor 54, since owing to length, but presenting an eifective capacity many skin effect none will now transversely through times as great as and apparently in parallel with the wall of the conductor, In so ?owing the cur that of the lower section, so that moving the rent meets an enormous impedance—say 100,000 slider to change the length of the section below it changes the apparent capacity as viewed from ohms. From there the line continues down the outside of conductor 54 to the antenna and back above relatively little. Therefore a very short length of the high impedance line above the within the column -51 to the terminus above the top of conductor 54. This latter length of line, 40 slider is all that is necessary to tune this e?ec tive capacity to resonance, thus completing the including the load imposed by the antenna, has quarter-wave section of line and bringing the an impedance of, say, 1 ohm, and since the volt node or quarter-wave point of the composite sec— age available at the termini of the line will divide itself across this low impedance and the high tion a small distance above the upper slider face. The distance between the slider and the node will impedance line section in series therewith in the vary with frequency, of course, but only slightly proportions of the magnitudes of those imped with the position of the slider. ances, and since the current ?owing at the input It has already been pointed out that the node points of the respective sections is the same, it is effectively equivalent to a short-circuit, and follows that the energy delivered to the respective impedances will also be in proportion to their 50 hence, since by moving the slider we may ‘move the position of the node, by so doing we may tune magnitudes, and only 1/ 100.000 of that delivered to the line will be transmitted to the antenna to be radiated thereby-still less if optimum con the uppermost section of the line including the ?lament and grid. We have made that portion ditions are met. of the line below the slider and above the im pedance loop relatively ineffective in tuning, so From still a slightly different aspect, the small and largely resistive impedance offered by the that we have an "elastic” or extensible quarter wave section of line. The ?nal or grid-?lament section may thus be resonated or otherwise tuned to give optimum the value of PR, is vanishingly small, the R in this case being the apparent input impedance of 60 operating conditions. In the case of Fig. 1, where capacity feed~back between anode l3 and grid the outer line and 12B (practically) the energy cap 99 is used, the desired tuning of this section radiated. must provide a capacitive reactance. This is From whatever aspect the matter be considered obtained by making the grid-?lament section the result is the same: The sections of the trans slightly longer than one-half wavelength or, in mission line above the current node terminate in other terms, tuning it to a slightly lower fre-‘ what is equivalent to an open circuit, just as quency than that of the desired oscillation, so would a low frequency line connected across an that as viewed at grid and ?lament it presents a ordinarily good insulator. There is some con small anti-resonant capacitive reactance. Under sumption of power, which can be neglected in fur ther consideration, (as in the case of the insu 70 these circumstances the ?lament-gridsystem ap pears as a capacity in series with the capacity lator) and the succeeding sections can be treated between the grid structure and the anode, and as if they terminated at this point in an in?nite outer line is at a current node. We therefore have a very small current ?owing, and therefore this latter capacity is adjustable by varying the position of the cap 99. When, therefore, the po an insulator for the line sections would drop the 75 tential of the anode swings, the grid will assume impedance. It should be noted, however, that at the frequencies we are considering substitution of 2,464,541 17 18 boundary grid, and anode, which elements are a potential with respect to the ?lament (and ground) which is intermediate between cathode and anode potential, and which bears the pro portion to the total potential between anode and ?lament that the effective series capacity between anode-grid and grid-?lament bears to the ap shown in'elevation in. Figs. 9, 15 and 13 respec tively; The accelerator grid is mounted from a side tube I05, which. is welded to project through the wall of the housing 5 immediately below the ?ange 3. This side tube carries at its outer end a ?ange I01 which is surfaced to receive the tubular ‘glass insulator we, and the latter, in parent capacity between ?lament and grid. In other words, the arrangement is essentially a capacitive voltage divider which swings the grid turn, carries a terminal flange H0. This struc potential in the same sense that the anode poten 10 ture may best be seen in the?enlarged detail view tial swings, and in ?xed and predetermined pro of Fig. 6. As in the case of the main tube en portion thereto. Since the criterion for oscilla velope, the tie-bolts which'hold the structure to tion of the device is that the grid and anode gether are omitted, but it will be understood that should swing in the same sense and in step, the it is assembled in the same fashion as is the main result is a highly effective capacity feed-back 15 envelope with ground surfaces reenforced by which is under control either by varying the ac greased rubber bands or gaskets I II ,which'form' tual capacity coupling with the cap 952 or by vary the seals. Two tubular conductors are ?xed to. ing the effective resonant input capacity of the and project inwardly from ?ange H 0. The inner grid-?lament circuit by varying the position of conductor I I2 is spaced from the outer conductor the slider 28. 20 H3 and is held accurately concentric therewith By the use of the two sliders the device is thus by an annular spacer H4. The accelerator grid given its very considerable tuning range. The I5 is supported from the‘inner member by a tubu lower slider El brings the current node to the lar bracket H5, the end of which ?ts within the point where the antenna is fed; the upper slider conductor H2 and is rigidly secured thereto. 'A 28 moves the nodal point immediately above it cooling pipe I", bent into‘ a ring to surround and thus tunes the ?lament-grid section. The the accelerator grid, has its ends brought ‘down actual point of importance is that by adjusting parallel to the support bracket H5 and enters the position of the sliders the effective resonant the inner‘ conductor on either side thereof, the impedance of the ?lament-grid combination may ends of the pipe passing into the ‘inter-conductor be made to assume any value which may be de 30 space distally of the spacer H4 and emerging sired, since the node above the slider 28 may be through the ?ange H0. A tuning slider H9, moved near enough to the rather large lumped which nearly, ?lls the space between ‘the inner cathode-grid capacity to embrace between the and outer conductors and does not make vactual node and that capacity the exact small line in contact therebetween, is operated by means of a ductance required for tuning it. In actual prac- ‘ hook I20 whose end projects through a longi tice the effective impedance will be made capa tudinal slot in the conductor H2. A controlrod citive and small in comparison with the phys~ I2 I is threaded to the end of the hook and emerges ical grid-cathode capacity, but it might, if de through a Wilson seal I22. ‘ sired, equally well be made inductive or resistive. The supporting bracket H5 and cooling tubes Furthermore, since the effective resistances in 40 I H. are carried up to the interspace between the the circuit are extremely low, the losses are also control grid and the boundary grid through an small even though the circulating currents may angular ?tting or shield I25, which passes‘through be large. ' a notch I 21 cut in one side of the ?lamentsup A system of transmission lines, chokes and by port ring 6i. This constructionris shown in Figs. passes similar to‘ that used in the ?lament-grid 1,6 and 11, each of these ?gures showing sections circuit is employed across the ?lament to prevent of the ‘shield. The shield is electrically con transmission of energy to D.-C. insulation and tinuous with a pan I29 overlying and contacting to prevent ?lament damage by R.-F. currents. the ?lament support ring; 14 and slotted im The actual ground point on the ?lament circuit is mediately above the ?laments, which forms an _ the ?ange ‘l on the outer casing 5 of the device. 50 additional shield or barrier to separate, com This, however, is unimportant and the e?ect of pletely the anode and control-grid sections of the the transmission line arrangement may be con tube except at the points where intercommuni- -' sidered as though the ground point were at the cation is necessary or desired. ‘The shield and inner end of the ?lament. This may be con pan therefore form one terminus, and the ac sidered as terminus of a quarter wavelength co 55 celerator grid and cooling pipe] I'I form the other axial transmission line comprising the tubular terminus of the radio-frequency transmission line conductors 19 and 80, which is open at its lower comprising the side tube I05 and the tubularcon end, terminating in a high impedance. The ductors H2 and H3. ' transmission line impedance is again low, being From what has gone before it is believed that of the order of, say, 5 ohms, and the line there 60 the operation of this arrangement will be readily fore forms a negligible series impedance as before, apparent. Again we have an antenna system acting as a Icy-pass to the inner conductor. This, comprising the control rods I2I and cooling tubes again, is a quarter wavelength line with the pipe I ll, plus the projecting end of the conductor‘ I I3, 62 as its inner conductor, terminating in a dead which is fed by and oifers a relatively high im short, and therefore o?ering very high imped 65 pedanceto a quarter wavelength transmission ance. As the potential imposed across this im line of low impedance formed by the side ‘tube pedance is merely that which can build up across I05 and the conductor H3, and there'is accord the short ?lament, amounting to a few volts at ingly a radio-frequency by-pass between the most, the escape of power through the ?lament grounded outer case 5 and tube I05 of the con support may be neglected, and the high imped '10 ductor H3. Within this there is another series ance effectively in series with the ?lament pre section of transmission line comprising the con vents circulation of R.-F. currents which might ductors H2 and H3 and terminating in a short otherwise cause hot spots and burn-outs. ' formed by the spacer-H4. = This v-inner line is We are now ready to consider the mounting of . tuned to a quarter wavelength byrmeans of the the remaining elements, i, e., the accelerator grid, slider I20, which acts as a loading capacity and 2,404,541 19 increases greatly the electrical length of the line. In practice this slider is moved back to a point from which the line appears as a very large in ductance at the operating wavelength. The proper point is that at which the remaining in ductance and capacitance of the line, considered from the grid end, make it just a quarter wave 20 Owing to the necessity for providing cooling the body itself must be water-tight, and accord ingly it is constructed of a ?ared cylinder I41, to the ?ared end of which the anode face I3 is hard—soldered. The other end of the cylinder is closed by a threaded disc I49. The supporting pipe I44 enters the ?ared cyl inder I41 through an aperture in the side thereof. The end of the pipe is threaded into a boss I48 I I4, forming a very high impedance at the shield where the grid I5 and cooling tube II‘! are sup 10 on an inner ba?ie cylinder I 50, which boss is soldered to the inner wall of the cylinder I47. ported, and preventing any appreciable power The boss I48 extends internally to form a cylin being transmitted past this point to be radiated. drical chamber !5 I , which connects by a side pipe The capacity of the grid I5 to the boundary grid I52 through the end I53 of the baffle cylinder, 4 is large, and that to the control grid I6 is small; so that water introduced through the pipe I44 is there is little coupling tending to swing the ac discharged directly against the active face I3 of celerator grid I5, and it consequently tends to the anode, and thence is forced around the ex maintain very nearly zero R.-F. potential. terior of the baifle cylinder to reenter its open As has already been described and as shown in end. It can then return within the cylinder to detail in Fig. 16 the boundary grid ii is ?rmly enter the open end of a return pipe I513, which clamped between the ?ange 3 and the anode length from the inner end to the shorting spacer housing 2, and is therefore physically and de? nitely at the ground potential of the housing. is mounted concentrically within the pipe I44 by means of a perforated cap I55 which ?ts over the end of the pipe I44, its lower end passing out The boundary grid and the anode face I3 again through the discharge chamber I5I. The cap form the termini of a resonant line, comprising the housing 2 as its outer conductor and a cylin 25 compresses a rubber gasket I46, sealing the joint between the pipe I44 and the anode body to make drical anode body, designated by the general ref it water and vacuum tight. erence character I39, within the housing. This The upper end of the pipe I54 is centered in resonant line is one-half wavelength long, and the pipe I44 by means of a metal bellows I57 may be considered as terminating between the inner face of the ?ange I and the end I35 of the 30 which is sealed to both pipes and. permits differ ential expansion between the two. Water is in anode body. This will be recognized as an open troduced into the pipe I44 through a side pipe I59, ended half wave line, and therefore of extremely and its course can be traced by the arrows in high impedance when viewed from either end. the drawings through the outer pipe, the perfo The construction and method of support of the rations in the cap I55, the side pipe I52, and anode body are best shown in Fig. 8. The sup thence around the bali‘le cylinder I50 and back port is from the mid- or quarter wavelength point through the central pipe I54. of the anode, i. e., at a potential node, so that The action of the mounting follows the prin there is little tendency for power to escape from ciples already set forth, although the application the support structure. Such tendency as there is is somewhat different. A disc I00 is connected for power to leak from the support point is sup to the ?ange I4! both electrically and mechan pressed by either or both of two methods. First, ically, and carries a cylinder ISI. The pipe I44 and preferable in the cases where the tube may be and the cylinders I 40 and IGI form a transmis predesigned to operate at a ?xed wavelength, is sion line one full wavelength long. Electrically a movable plate I32 mounted on the sliding rod this might equally well be a half wavelength line, 59 of the Wilson seal ?rst described, and making 45 but additional space is needed for the insulat contact with the ?ange I by means of a spring ing cylinder I42, which must withstand the full skirt I33. This may be adjusted to bring the node D.-C. anode potential of 20,000 volts or more. of the resonant line accurately at the point of The length of this section is measured from the support. This method of preventing direct radia anode and its housing, and the impedance at its tion from the anode was adopted in the ?rst outer end is very high, so that looking into it of these devices constructed. It was quickly from the anode the impedance is also very high. found, however, that the plate I32 was more use This high impedance is connected in shunt ful as a tuning device, and therefore the prin across the line formed by the anode body I 30 and ciple of transmission-linerchoke support was again employed to prevent power escape. In the 55 anode housing 2 very near the nodal point, where the impedance of the latter line- is low, and ac construction then adopted and here shown a cordingly a very small portion of the current side tube I40 of relatively large diameter is welded ?owing at this point will take the high imped at substantially the midpoint of the anode hous ance path to the outer world. ing 2. The side tube carries a metallic ?ange In other terms, the full wave line is connected I4I, with a glass insulator tube I42 ?tted against 60 so near the node Of the main anode oscillator it and in turn carrying a terminal ?ange I43. circuit that only a few volts are eifective across Through this terminal ?ange passes a pipe I44 its termini, and therefore very small currents will which projects through a pass hole I45 in the tend to ?ow therein, representing a power loss of side of the anode housing and on the end of which V2 the anode body is attached. The action here will ‘5 be described following the mechanical description of the anode, as the expedients adopted are pred where V is the small input voltage and Z is the icated upon the necessities of the mechanical large input impedance. Moreover, since the line structure. is one wavelength long, only the small voltage From the electrical point of view the anode 70 V will be effective to cause radiation from the body is a simple cylinder with closed ends. Its radiating system constituted by the end of the complexity, as shown in Fig. 8, is due primarily line. It should be noted, however, that by de to the provision for circulating cooling water liberately unbalancing the anode resonator by within it, and to the provision of what may be means of the plate I32 the support systemcan 75 be converted to a horn ‘antenna which can be termed a “rough tuning” device.