US2213177A

US2213177A - Television transmitting tube

Info

Publication number: US2213177A
Application number: US280999A
Authority: US
Inventors: Harley A Iams
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1939-06-24
Filing date: 1939-06-24
Publication date: 1940-08-27
Anticipated expiration: 1957-08-27
Also published as: NL67098C; GB543890A

Description

Allg. 27, 1940. AY |AM$ 2,213,177

TELEVISION TRANSMIT'ITNG TUBE Filed June 24, 1939 2 Sheets-Sheet l #9999999039 NNI INVENTOR. Z HARLEY A. [AMS ATTORNEY.

A? w 111414 444141 111141111 1 `QN QVGQW f .F Xulqbm.

Aug. 27;' 1940. H. A. IAMs 2,213,177

wTELEVISION TRANS'MITTING TUBE Filed June 24, 1939 2 SheetsSheet 2 INVENTOR. HARLEY A. [AMS BY @W l ATTORNEY.

Patented Aug. 27, 1940 TELEVISION TRANSlVIITTING TUBE Harley A. Iams, Berkley Heights, N. J., assigner to Radio Corporation of America,a corporation of Delaware Application June 24, 1939, Serial Noi-280,999

9 Claims.

' My invention relates to television transmitting tubes and is more particularly directed to tubes Autilizing low velocityelectron scanning beams and incorporating .electron .multiplier arrangements.

Television transmitting tubes of the low velocity electron beam scanning type have. been made in which a combination magnetic-electrostatic deflection system including electrostatic plates wholly immersed in a uniform axial magnetic eld shifts the beam in a plane parallel to the plates. Such tubes have not been satisfactory when made to incorporate electronA multiplier elements because the electrons directed toward the .target electrode return along dissimilar paths and are distributed'over along line or over an area substantially as large as the target. The electrons could not be collected over a relatively small area andthe fullest advantage of electron multiplication could not be obtained. A further limitation to the amplication which can be given the signals from a television pick-up tube is the level of other disturbing signals or noises. In such an arrangement as above described the optimum ratio of picture to noise signal is not obtained when the initial amplication is obtained by means of an electron multiplier located Within the pick-up tube because photo-emission from the targetis multiplied along with the electrons representing the signal energy.

It is an object of my invention to provide a television transmitting tube of the low velocity electron beam scanning type wherein electron multiplication may be utilized to its fullest advantage. It is another object of vmy vinvention to provide such a tube wherein the electrons not reaching the target may r'be intercepted over a Arelatively small area outside of the region between the electronv source and target for electron multiplicationpurposes. It is a further object to provide a low velocity electron beam scanning tube wherein energy representative of the desired signals may be separated from nonsignal energy, and it is a still further object to provide a tube wherein the signal may be amplifled by electron `multiplier arrangements while keeping the noise distortion at a minimum value In' accordance with my invention, an electrostatic image corresponding in electrostatic energy distribution to the light distributienet an opticalV image is formed on a target or mosaic electrode which is scanned with a low velocity `electron beamy from an electron source su'ch as an electron gun, the scanning being accomplished 'inl a combination magnetic-electrostatic eld in such amanner that a portion of the electrons directed toward the target electrode return toward the electron gun along dissimilar paths and over a relatively small area so that an electron multiplier in= the path of the returning electrons receives no energy except that representative of the returning electrons which are modulated in intensity by the electrostatic image formed on the target. More particularly in accordance with my invention, I provide a structure which separates the electrons representative of signal energy from other electrons generated during the normal operation of the tube.

A better understanding of my invention will be obtained and other objects, features and advantages will appear from the following description taken in connection with the accompanying drawings in which:

Fig. 1 is a cross-sectional view of a televison transmitting tube and circuit embodying my invention, Fig. 2 is an elevation perspective View of the tube shown in Fig. 1, Fig. 3 is a plan perspective view showing a modification of my invention, and Fig. 4 is likewise a plan perspective view of a tube incorporating another modication of my invention.

In general, the apparatus of my invention comprises an evacuated envelope having. a target preferably of the photosensitive mosaic type at one end thereof andan electron gun and electron multiplier at or near the opposite end of the envelope, The target,v if of the mosaic type, is provided on its front surface with an extremely large number of mutually insulated photoelectrically sensitized particles and is so positioned that it may be scannedV by an electron beam from the gun yand may also have focused upon it an optical image of the object of which a picture is to be transmitted. The electron gun is of a conventionall type andv is preferably displaced from the center line of-v the tube so that it will not be in the path of electrons returning from the target. The potential between the electron gun and target is sol adjusted that the electron beam is projected at relatively low velocity and directed upon the target at extremely low or substantially zero velocity, that is,l at a velocity approaching: zero at thel point ofv impact therewith. The electron multiplier is pref- ,erably offset from] the center line between the tensity of the light incident thereon, thus particles of the mosaic which are more highly illuminated acquire the more positive electrostatic charges with respect to the unilluminated particles, and these positive charges which represent an electrostatic image of a picture to be transmitted are neutralized by a portion of the low Velocity electrons in the scanning beam, the remaining electrons being reflected from the target. Intermediate and extending wholly between the electron gun and the electron multiplier with respect to the target, I provide a uniform axial magnetic eld and means Within the eld to generate an electrostatic field to scan the electron beam from the gun over the target and cause the electrons returning from the target to be directed over dissimilar paths to the relatively small area occupied by the electron multiplier. Since the electron gun and electron multiplier are offset one from the other, the advantages of such an arrangement to be hereinafter described, means are provided for lifting the electron beam from one path to another path which is lparallel with the first path so that the beam may be scanned over the target and a portion returned along dissimilar paths to the relatively small area occupied by the electron multiplier.

Referring particularly to my tube structure as shown in Figs. 1 and 2, the tube includes an elongated evacuated envelope enclosing at one end a target or mosaic electrode 2 and at the opposite end, an electron gun assembly 3 adapted to project electrons toward the mosaic electrode and, at the same end as the electron gun opposite the mosaic electrode 2, an electron multiplier 4 offset from the electron gun in a direction transverse to a direct line between the electron gun and the mosaic electrode.

The mosaic electrode 2 which faces the electron gun preferably comprises a substantially transparent sheet of insulation such as the mica sheet 5, having on its rear surface a translucent or semitransparent electrically conducting film 6, the front surface of the mica sheet being provided with an exceedingly great number of mutually separated photosensitive particels 1. In making the mosaic electrode I select a mica sheet 5 of the desired area and having a uniform thickness of approximately .002 inch, and as a lst step coat one side of the sheet with an electrically conducting lm of metal of sufcient thinness as to be substantially transparent so that an optical image such as represented by the arrow 8 may be focused on the photosensitive particles 7 by the lens system 9. The mosaic of mutually separated particles may be made in a number of ways well known in the art such as by depositing on the sheet of mica finely divided silver oxide which is reduced by suitable heat treatment and formed into the mutually separated and insulated particles l following which the particles may be oxidized and sensitized with caesium or other alkali metal during the evacuation of the tube. Such an electrode structure and a method of sensitization is disclosed by S. F. Essig in U. S. Patents 2,020,305 and 2,065,570.

rIheelectron gun assembly 3 is of a conventional type and comprises a cathode I from which electrons may be drawn, a control electrode II connected to the usual biasing battery, and a rst anodeI2 maintained positive with respect to the cathode I0. The electron stream leaving the rst anode I2 is accelerated at relatively low velocity :and concentrated into an electron scanning beam focused on the front surface of the target or mosaic electrode by the axial magnetic field and the electrostatic eld from a second anode I3 which is preferably an apertured tubular member partially surrounding the rst anode I2. The first anode I2 and the second anode I3 are maintained at the desired positive potential with respect to the cathode by a battery I4. The cathode ID is preferably connected directly to the electrically conducting lm of the mosaic electrode so that this conducting film may be maintained at cathode potential, although the conducting film 6 may be maintained slightly positive or negative with respect to the cathode.

In accordance with my invention the electron multiplier 4 is located near the electron gun, that is, oppositely disposed from the mosaic electrode 2 and out of the path of the beam projected from the electron gun to the mosaic electrode for all positions of the scanned beam. The electron multiplier is thus offset from the electron gun structure While, at the same time in accordance with my invention, it is capable of receiving electrons directed by the electron gun toward, but not reaching the mosaic electrode.

The electron multiplier 4 may follow one of the well-known designs, such as a structure which comprises any desired number of perforated electrodes such as the wire mesh screens I5, I6, I'I and I8 interposed in the order named between the mosaic electrode and an electron collecting electrode or anode I9. These wire mesh screens are constructed of bright nickel or of other material having good secondary electron emitting properties. For ease in assembly I prefer to support the wire mesh screens by concentric

metallic cylinders

20, 2|, 22 and 23 which are in electrical contact with their respective wire mesh screens and connected to a potential source such as the battery 24 through a bleeder resistance 25, the wire screen I5 and its associated supporting cylinder being connected to ground and consequently to the anode I3. The electron collecting electrode or anode I9 serves as an output electrode for the tube and is connected through an output impedance 26 to an input electrode of a translating device 26 and to the positive terminal of the battery 24 so that signals generated in the tube may be amplified and applied to a transmission network as Well known in the art.

In accordance with my invention I provide intermediate the electron gun and the target or mosaic electrode means to deflect the beam and further means to raise the beam so that it irnpinges on or is directed toward points of the mosaic electrode outside of the direct line between the gun and mosaic electrode, the latter means simultaneously serving to raise the electrons of the beam not reaching the target to a plane parallel to the plane in which the electrons are deflected so that they may be directed toward the electron multiplier over paths dissimilar from those along which they approach the mosaic electrode. In addition, I provide further deflection means to absorb the deflection produced by the rst deection means, that is, to deflect the beam in the opposite direction and by an amount equivalent to the rst deflection and in a plane parallel with the plane of the first deflection.

This deflection, however, is in an opposite direcs tion than that afforded by the first deflection so that the returning electrons may be directed to a point offset from their point of origin in the electron gun at which point is located the electron multiplier 4. To provide proper functioning ofthe beam deection means, I provide a magnetic coil 21 which completelysurrounds the envelope I to generate a magnetic field having lines of force parallel with the center lines between the multiplier and electron gun to the target. This iield extends over and preferably beyond the space separating the electron gun and electron multiplying structure from the mosaic electrode.

More particularly, and again referring to Figs. l and 2, I provide deflection plates 28-29 positioned between the electron gun and the mosaic electrode, one on either side of the direct path be* tween said electron gun and mosaic electrode. Another deflection plate 3D coextensive with and parallel to the plate 29 is located on the side of the plate 29 opposite the plate 28 so that the plates -29-39- are on opposite sides of the direct path between the multiplying structure 4 and the mosaic electrode 2. The

plates

28 and 39 are connected together and with the plate 29 are connected to a source of deiiection potential and to ground through a center-tapped resistance 3| which may be of the order of 1 to 10 megohms. Thedeflection plates 28-29 are wholly immersed inthe magnetic iield generated by the coil 2l. Asthe electrons from the electron gun pass into the combination magnetic-electrostatic eld between the plates 28-29, the electrons are deilected in a plane parallel with the plates and follow a path Such as represented by the dashed line 92.

lFurther in accordance with my invention, I provide in the space separating the

plates

28, 29 and 30 from the mosaic electrode 2, a pair of lifter plates 33--34 which are widely separated transverse to the tube axis and located in planes substantially perpendicular to the plates 28--39 and to the plane of deflection between the plates 28-29. As the beam passes from the deflection plates 2'8-29, it passes along parallel paths by reason of the axial magnetic field, such a path being represented by the line 35, and into the field of the lifter plates i-34, whereupon the beam follows a path 36 which is inclined at an angle to the plane of deflection between the plates 28-29. After the beam leaves the iield between the plates 33-34, it approaches the mosaic electrode 2 along parallel paths by reason of the axial magnetic field and by reason of the deflection potentials applied to the plates Ztl-29, which beam may be made to trace a single line Io-f elemental beam width over the mosaic electrode. It will be observed that the lifter plates 33-34 perform a double function, namely, to lift the beam to a plane parallel with the plane of deflection and through the tube axis such as a plane through the plate 29 and to further lift the electrons reflected from the mosaic electrode to a plane parallel with and substantially midway between the plates 29-30. It will be ob- Viousthat both plane surfaces of the plate 29 are utilized to produce, in combination with the adjacent `surface of the plate 28 and of the plate 30, electrostatic fields which are utilized in the operation of the device. I may therefore choose to use two closely spaced or contiguo-us plates in place of the single plate 29. Thus the plates 28-29 may be referred to as means to deflect the beam in a unidirectional manner and the plates 29-39 as means to absorb the deflection ,imparted to the electrons by the plates ZS-ZEL In order to obtain scanning in a direction normal to the scanning produced by the plates 2li-29, I provide between the lifter plates and the mosaic electrode a pair of magnetic deflection coils 38-39 so that the beam may be scanned over any desired area of the mosaic electrode.

During operation the light or image such as represented by the arrow 8 projected on the mosaic electrode liberates photoelectrons from the particles l in proportion to the light intensityl on the individual particles, and since the electrically conducting film 6 is operated at or near cathode potential, the electrons approaching the mosaic electrode such as along the path il are decelerated and proceed toward the mosaic electrode with a velocity approaching zero. The electrons directed toward the particles 1 which are `positive with respect to the cathode will be collected by the particles, whereas electrons approaching unilluminated particles on the mosaic will be reiiected from the mosaic along paths such as represented by the line 4D, which are initially substantially coincident with the paths of approach to the target. Since the plates 28-3@ have a mean ground potential, the electrons are drawn from the mosaic electrode with increasing velocity as they leave the vicinity of the mosaic electrode and are drawn into the eld between the lifter plates 33-34, whereupon the returning electrons are lifted by an amount equivalent tothat by which they were lifted over the path 36 to a new path such as represented by the line M. 'Ihe electrons then follow substantially parallel paths, one such as represented by the line ft2 in a plane parallel with the plates 29-39 and midway therebetween. Since the electrons are moving in a direction Opposite to that followed while moving toward the mosaic electrode and since the plates 2S and 39 are interconnected and supplied with de- Iiection potential with respect to the plate 29, the returning electrons are deflected along a path 43 by an amount equal to the deflection along the path 32 and are directed into the electron multiplier 4. 'I'hose electrons which impinge upon the wire mesh screen l5 of the multiplier l release a great number of secondary electrons which are drawn toward the wire mesh screen IG where the energy is similarly multiplied since the electrons are subjected to a higher potential field generated by the battery 24 and impinge on the wires of the screen It. Similar electron multiplication takes place from the wire mesh screen Il and E8, whereupon the electrons are may be used, and I do not wish to be limited to the particular structure shown.

Since the plane of deflection between the plates 28-29 and the plane of deflection between the plates 29-39 are parallel and equidistant, the space being determined by the distance the electron gun is offset from the electron multiplier, the amount of lifting imparted to the beam between the plates 33--34 along the path 36 is equivalent to the lifting of the beam along the path lll, and consequently, I desire to maintain a uniform potential gradient between the plates 33-34 so that the amount of lifting will be the same for all potentials applied between the deflection plates 253-29. The plates 33-34 are therefore connected through a center-tapped bleeder resistor M to a potential source such as the battery 55. While I have shown the polarity of the battery 15, reversal of the magnetic field generated by the coil 2l will necessitate reversal of this polarity. It is also desirable that the electron beam pass between the lifter plates in a region of constant potential even though the beam is deflected horizontally by the deiiection plates. I therefore prefer to apply a small amount of the horizontal deflection potential across the lifter plates 33-34 so that the beam while passing between the lifter plates passes through a zero potential gradient with respect to ground. To accomplish this mode of operation I connect the center tap of the bleeder resistor 44 to a point on the resistance El close to the grounded center tap of this latter resistance. While I have shown this connection as being made to the left of the grounded center tap of the resistor 3i, the connection is made to the opposite side of the center tap if the direction of the axial magnetic field produced by the coil 2 is reversed.

While I prefer to locate the electron gun in the region of the electron multiplying structure as shown in Figs. 1 and 2, the arrangement wherein the electron gun and multiplier are offset along the axial magnetic field as shown in Fig. 3 offers certain advantages. Referring to Fig. 3 wherein the electrode structure corresponding to that shown in Fig. l is similarly referenced, the electron gun 3 is located in an offset manner from the center line of the tube and offset from the deiection plates Sil-5i. In this construction I provide lifter plates 52-53 connected to a source of D. C. potential between the elec'tron gun and the deflection plates -EL In operation the electron beam from the gun is directed toward the mosaic electrode 2 and into the field between the lifter plates 52-53, whereupon the beam is lifted such as along the path 55 into a plane substantially midway between the deflection plates 50-5I, whereupon the beam is deflected in a plane parallel with the plates along the path 55 and subsequently along a path 56 toward the mosaic electrode. For purposes of clarity I have not shown the coil 2"! used to generate the axial magnetic field nor the coils 38-39 used to deflect the beam in a direction perpendicular to the direction produced by the plates E@ 5L The electrons not reaching the mosaic electrode return along paths such as represented by 5l substantially coincident with that represented by 5S and enter the deflection field between the plates SGL-5l, whereupon they are deiiected by an amount equal to the deflection along the path 55 as shown at 58. It will be evident that the beam suffers no further deflection after it leaves the eld between the plates EEE-5l along the path 56, so that for maximum deflection of the beam across the mosaic electrode, that is, in a horizontal direction, the plates 5KB-5i should be at least as wide as the mosaic electrode, both of these directions being in the plane of the plates and no1'- inal to the tube axis. Since, however, the deflection of the electrons returning from the mosaic electrode along the path 5S is equivalent to and in the same direction as the defiection along the path 55, the deflection plates must be at least twice as wide as the effective width of the mosaic electrode.

In accordance with the modication of my invention shown in Fig. 3 I provide means such as a further set of deflection plates 553-66 on the opposite side of the deflection plates '5S-5E from the mosaic electrode 2 to absorb the deection imparted by the plates 59-5! to the electrons of the beam which are unabsorbed by the mosaic electrode. The plates 59-65 are preferably in the same planes as the correspondingly positioned plates 50-5I. The two sets of deflection plates are interconnected so that the plate 50 is tied to the plate 6i) and the plate 5l to the plate 59, the source of horizontal deection potential being applied to the two sets of plates as shown in Fig. 3. After the returning electrons pass along the path 53, they leave the deflection field between the plates 50-5i and follow parallel paths into the reverse field between the plates 59-66, whereupon the electrons are deflected in a plane parallel with the plane of deflection between the plates 50-5! along a path such as the path 6I to the electron multiplier 4 where the energy representative of these electrons is multiplied, collected and fed to an amplifying arrangement as shown in Fig. l. Since the deflection between the plates Sil- 5I along the paths 55 a-nd 58 is cumulative, the deflection plates 59-60 should likewise be at least twice as wide as the mosaic electrode or as wide as the deflection plates 5D-5l and should have a length twice the length of the plates Sil-5I, since the lateral displacement of the electrons along the path 6| is equivalent to the combined displacement along the

paths

55 and 58.

Another modification of a television transmitting tube made in accordance with my invention is shown in Fig. 4 wherein the electron gun 3 and the electron multiplying structure are similarly positioned as shown in Fig. 3. Electrode structure similar to that shown in Figs. l, 2 and 3 is similarly referenced and I have again omitted showing the magnetic coil 2T and the vertical deiiection coils 38-39 for purposes of simplicity.

The path of the beam as it leaves the electron gun passes through the lifter plates 52-53, the deiiection plates 5il5i, and a portion of the beam returns through the deflection plates Ell-5I along paths similar to those shown in Fig. 3. After the returning electrons leave the field of the plates 50--5|, they are directed along parallel paths in the plane of deflection produced by the plates Sil-5l toward the electron multiplier 4 which is located along the tube axis and in the plane of deflection. Between the electron gun 3 and the multiplier 4 I provide means such as a system ofy deflection plates immersed in the magnetic field generated by the coil 21 to absorb the deflection energy imparted by the plates 50-56 to the electrons of the beam which are unabsorbed by the mosaic electrode. This system of plates comprises the cross-connected plates 62-63 and the cross-connected plates 64-65. The two pairs of cross-connected plates are connected to a suitable source of D. C. potential. While I have shown the polarity of the D. C. potential applied to the two pairs of crosscon nected plates, the polarity should be reversed for a reversal of the field developed by the coil 2l.

In operation of the tube shown in Fig. 4, the electrons returning from the deiiection plates 50-5l such as along the path 66 enter the deflection field between the plates 63-65, and since these plates are cross connected and the polarity of the D. C. voltage is suitably chosen, the returning electrons are directed toward the tube axis. At the time or shortly before the electrons reach the tube axis they leave the deflection field between theplates 63-65 and are controlled solely by the axial magnetic field, whereupon they travel parallel with and along or close to the tube axis and are collected by the electron multiplier. If, however, the -deflection is on the opposite side of the tube axis from that shown in the drawings, the plates (i2-64 will direct the returning electrons toward the tube axis, whereupon at the time or shortly 4before the electrons reach the axis they are controlled solely by the magnetic field and proceed to the electron multiplier.

- WhileI do not wishfto be limited to the particular/theory which Ifhavev evolved to explain the improved operation of my device, itv seems probable J that thev electrons which are directed toward the -zmosaic electrode are modulated in accordancefwth the' electrostatic energy distribution produced on the mosaic 1 electrode in accordancexwith. the light and shade oi" the optical imagev The electrons returning from the mosaic electrode aredirected along definitely controlled paths differing from the paths along which the electronibea'mV approachedthe mosaic over the y major length ofthe tube vand are collected over the relatively small 'area occupied by the electron multiplyingv structure. In this wayit is possible 'to collect all of the returning electrons so that electron'multiplication may be effected. The photo-electronsliberated bythe mosaic electrode under the influence'of light are accelerated toward the electron multiplier, but substantially all of these 'photo-#electrons are collected either by thefdeflection plates or by a grounded conductive wall coating (not shown) in the region of the mosaic electrode which may extend over the entire length of the tube. Very few of the photoelectrons return to the multiplier because the combined magnetic-electrostatic fields lift and deflect these electrons from' the paths to the electron multiplier. Thus while a few photo-electrons under conditions of Zero deflection may be intercepted by the electron multiplier, it is impossible for the large.'A majority of these photoelectrons to be collected on the output electrode nor is it" possible for them to enter the multiplier Wliere their energy might be amplified and produce distortion of anappreciable amount.

1. Atelevision transmitting tube comprising an elongated envelope, a target electrode adjacent one end of the envelope adapted to have an optical image focused thereon, a system of electrostatic eld generating plates between said target and the` opposite end of said envelope from said target, said system of plates including acentral and'twc outerplates spaced apart in a direction lnormal to the longitudinal axis of said tube, an electron gun adjacent the edges of the central andfouter plate of said plates opposite from said target to develop and direct a beam of. electrons between saidl central and outer plates, an electron collecting electrode positioned adjacent the edgesof the central plate and the remainingb outer plateA opposite from' said target to receive electrons 'from said gun not reaching said target, means to generate a magnetic field having lines of force extendingfrom said electron gun and collecting electrode to said target, and a pair of plates intermediate the said system of plates and said target for, in combination with said field, deflecting said beam and the electrons returning from said target in a direction normal to the original direction of deflection of the beam produced by said central plate and said one outer plate' and to the direction of said returning electrons within said central plate and the said remaining outer plate.

2. A television transmitting tube comprising an elongated envelope, an electron gun and a target electrode adjacent opposite ends of said envelope, a magnetic focusing coil surrounding said envelope to generate a magnetic field having lines of force parallel with the center line between said gun vandgtarget, meansA comprising a rst pair of deflection-.plates each plate of saidy pair being positionedion Veitherside of the pathl between said gun andftargetato deflect the beam over saidtarget in ai directionv parallel with said plates, a pair of platesLsubstantially perpendicu` lar to the planesv of said flrstpairof plates tolift first pair of plates to the electronsof the beam,

and electron collecting means removedl from the path between said gun and-target to collectthev electrons returning'from said target. v

3`. A television transmitting tube comprising an elongated envelope, a target electrode",v means to project an optical image on said target electrode, an electron `gun oppositely disposed from said target electrode to g'enerateand direct a beam of electronstoward said target, means to *gen' erate a magnetic field' having lines of yforce substantially parallel to' the undeflected path of said beam, a pair of spaced parallel plates, one on either side of the path of sa-idbe'am to deflect the beam in` a plane parallel "with the plates, means to deflect the electron beam'` from the plane of 'deflection betweensaid plates toa `plane substantially lparallel 'therewith and to" deflect electrons not reaching said'target toanother plane parallel with said'first-mentioned plane'v of deflection,"means including onevof said plates to deflect the electrons, .which return from' said target, in a direction opposite fromI that` pro duced by said iirst'pairof plates and means in the path of said returning electrons to electron' ically multiply the returning electrons to generate electrical currents representative of'elemental areas of said optical image, l c

4. A television transmitting tube comprising an elongatedV envelope',A a target electrode adapted to havean optical imagefocused thereon from a pointv outside said envelope, an electron gun offset kfrom the longitudinall axisof said tube to generate an electron beam, means in the path -of said beam' to 4displace said?. beam to a path substantially coincident withfs'aid longitudinal axis, means including'a'pair of deflecton plates to deflect the beam inaplane parallel with the planes ofthe plates, means moreremoved ,from Vsaid target than said electron 'gun to deiiect 'the electrons of the beam not reaching the target, in a direction opposite to the deection imparted by said pair of plates to the electrons reaching said target, means to intercept the electrons returning from said target after the deflection produced by said last mentioned means and means to generate a magnetic field having lines ofrforce extending substantially normal to said target and extending from said target to said electron intercepting means.

5. A television transmitting tube comprising an electron gun to develop a beam of electrons, an oppositely disposed target .electrode adapted to have an optical image focused thereon and to be scanned with the electron beam from said gun, means to generate a magnetic field having lines of force parallel with the center line between and intercepting said gun and target,

means-.including a pair of'oppositely disposed plates, one on either side of'aportion of the path ofthe electronbeam. between said gun and target to scan'saidbeam-over'said target, a collecting electrode-to collect electrons of the beam not reaching said. target:whollyremoved from the pathofsaid beam'when scannedover said target by^ said plates;A and a second pair of plates wholly-immersed in said magnetic field to direct the electrons not' reaching said., target to said collecting electrode.

6. A device for generating television signals comprisingian evacuated'envelope'having a window; a` target including a mosaic. of mutually separated: photosensitive. particles positioned to havefan'optical image formed thereon through said window, an electron, gun in said envelope oppositely.disposedfronrsaid window and said target'to'generate and 'direct'an electron beam toward-said'` target; magnetic means to constrain the electronbeam and direct it along a path normalwto: said target*y an pair of oppositely disposed electrostatic `deection` plates associated with said last-named'meansito deiiectn the beam from the said pathv infav plane'parallel with said plates, means to displace'thev deiiected beam into a plane parallel with butspaced from said first-mentioned. plane'tosscan said` target, means to deflect the-electronsnot reachingsaid target in a direction opposite to the deiiection produced by said iirst-mentioneddeiiection to a point'outside ofi-the' paths followed by said beam from said gun to said-target to 'return-said electrons over a relativelysmallarea,A and-electron collecting means acrossl the '.path of the electrons returning from said. target.

'7. A'television transmitter comprising an evacuated: envelopeahavinga window therein, an electron emissivey light sensitive target positioned to receive an optical image through said window, an electronhgun postioned within said envelope to develop and project an electron beam toward said targetwithafl velocity approaching zero in the vicinityofsaidatargetfmeans to generate a magnetic eld havinglines:otforcenormal to said targetand. extending at least between said gun and,k target, a. pair ot electrostatic deflection plates wholly immersed ,in saideld one of said plates being on. each'side of a portion of the beam path to, deflect andscan the beam over said'target, means Acomprising a second pair of plates whollyv immersed, in said field and over another portion of the beam path to prevent electrons not reachingV said first-mentioned target from,returning along the paths followed by the beam between said deflection plates and means wholly removed from the paths followed by the beam during scansionof said target, to collect the electrons not reaching said target.

8. A device for generating television signals comprising an elongated envelope having a window, a target includingVV a mosaic of mutually separated photosensitive particles exposed to said window to have an optical image formed thereon through said window, means surrounding said envelope to generate a magnetic field having lines of force substantially perpendicular to said target, means outside of a path normal to and intercepting said target to generate an electron beam, means along the path of the beam' and wholly immersed in said field to displace the beam into a position directed toward said target, deflection means including a pair of spacially separated plates wholly immersed in said iield to deflect the beam in one directionY overl said target, means to deect the beam in a direction substantially normal to the deflectionproduced s by said pair of plates, a system of deection plates more remote from said target than said beam generating means to deflect the electrons of the beam not reaching said target, in a direction opposite to the deection imparted byl said iirst deection means and means more remote from said target than said gun and said system of plates to collect the electrons not reaching said target.

9. A television transmitting tube comprising an elongated evacuated envelope enclosing a target having mutually separated photosensitive particles adapted to have an optical image focused thereon, an electron gun displaced from the` longitudinal axis of said envelope to generate and project an electron beam in the direction of said target, an electron focusing coil surrounding said envelope to generate a substantially uniform magnetic eld having lines of force parallel with said longitudinal axis, means to deflect the beam of electrons at a substantially constant angle toward said longitudinal axis, a pair of .deflection plates, each of which are positioned onopposite sides of the said axis to defleet the beam over said target and to deflect electrons not reaching said target from the paths followed by said beam while passing through said plates, two pairs of plates more removed from said target than said gun, each pair of said plates lying in a planeparallel with said first-mentioned deecting platesv and4 on opposite sides of said axis, .the .plates of onepair being opposi-tely disposed from the plates of the other pair to return the electrons not reaching said target to the saidaxis and means along the axis of the tube to collect the returning electrons.

HARLEY A. IAMS.

CERTIFICATE oF CORRECTION.. Patent 1m,v 2,215,177. August 27, 191m.

HARLEY A. IAMS.,

` It is hereby certified that error appears in'the printed specificationof the above numbered patent requirihg correction as follows: Page 6, first column, line )4.8, claimt?, after' the word "field" insert a comma; line 514, same claim, strike out "first-mentioned" and insert the' same before "dele ctionp in line 56,- same claim; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in' the Patent Office., y signed 'and sealed this .11th @gy of February, A. D. 19m.

. Henry Van Arsdale, (Seal) n Acting Commissioner of Patents;