US2249552A - Electron tube - Google Patents

Description

July l5, 1941. v. K. zwoRYKlN ELECTRON TUBE Original Filed Dec.l 24, 1950 4 Sheets-Sheet 1 July 15, 1941. v. K. zwoRYKlN 2,249,552

ELEoTRoN TUBE Original Filed Dec. 24, 1930 `4 Sheets-Sheet 2 INVENTOR f VL'AD/M/R ZWORYK/N BY 71%,@ Wav ATTORNEY July 15, 1941.

V. K. ZWVORYKIN ELEcTRoN TUBE original Filed Dec. 24, 1930 4 Sheets-Sheet 3 D/srANcEAzoA/G Ax/s of russ //ELD F/RST NDE INVENTOR VLAD/M/ zWoRYK/N BY ,www

ATTORN EY E 6 m m m e 6 July 15, 1941. v. K. zwoRYKlN 2,249,552

ELEcTRoN TUBE Original Filed Deo. 24, 1930 4 Sheets-Sheet 4 67 INVENTOR ATTORNEY A Patented July 15, 1941 ELECTRON TUBE Vladimir K. Zworykin, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Original application December 24, 1930, Serial No. 504,559. Divided and this application June 21, 1937, Serial No. 149,463

(ci. 25o- 275) 6 Claims.

United States Patent NO. 2,109,245, is utilized, the

received picture impulses are impressed on the grid of the tube to control the intensity of the ray in accordance with conditions of illumination of the individua1 spots or regions making up the object at the transmitter. The electrons making up the ray move from the cathode, and pass through a relatively small aperture in the control grid to the so-called first anode of the tube, from whence they are directed toward a fluorescent screen at the larger end of the tube. The electrons are caused to travel from the cathode to the rst anode at a relatively high velocity, which is increased or stepped up to a much higher velocity by a second anode which, for this purpose, has in some cases been maintained at a positive potential of about 4,500 volts, the first anode, in such cases, being maintained at a positive potential of about 1,000 volts. The relatively high volatge gradient along the axis of the tube between the cathode and the first anode, corresponding to conditions Whereat the potential on the first anode is maintained at about 1,000 volts, has heretofore made necessary the provision for relatively high voltages on the grid to control the cathode ray completely, the voltage variation lying in a range between 30 and 45 volts.

For the purpose of providing for these relatively high grld-control voltages, it has Ibeen necessary to utilize high gain audio amplifiers in the radio receiver. These amplifiers are expensive, and furthermore, operate to distort the received picture appreciably.

In the various constructions of cathode ray tubes used heretofore in television receiving systems, the maximum effect or inuence of the electrons making up the cathode ray has not been effective with respect to the fluorescent screen to develop the light image. This is attributed to substantial leakage of electrons from the cathode to the second anode, around the first anode. That is, in these cathode ray tubes constructed heretofore, the electrons, after passing through the control grid, have a more or less pronounced tendency to depart from their path of travel in the ray and take a. new path of travel around the first anode instead of passing through -the anode aperture for effective impact with the fluorescent screen.

With the foregoing in mind, it is one of the objects of my invention to provide an improved television system of the general character referred to, and apparatus therefor, wherein the grid voltage for complete control of the cathode ray is substantially lower than that required in the various systems proposed heretofore, the grid voltage in the present improved system being suiciently low to permit direct connection of the control grid with the radio receiver and the associated radio-frequency ampliiler, thereby obviating the high-gain, expensive and troublesome audio ampliers required in the systems of the prior art.

Another object of my invention is to provide an improved television system, of the general character referred to, wherein the cathode ray tube, forming part of the system, functions as its own detector of the incoming modulated carrier wave to supply picture impulses to the control grid, and, if desired, to supply simultaneously the synchronizing impulses to the electromagnetic or other means for causing the ray to scan the fluorescent screen structure.

Another object of my invention is to provide an improved television system of the general character referred to, which has advantages over the various systems proposed heretofore in the way of simplicity, cost of manufacture and electron control. l"

Another object of my invention is to provide improved cathode ray apparatus of the general -character referred to wherein the percentage of electron leakage from the cathode to the second anode, around the first anode, is practically negligible, so that there is substantially maximum efficiency in the way of complete utilization of the electrons for the purpose of developing the light image on the fluorescent screen.

Other objects and advantages will hereinafter appear.

In accordance with my invention, the voltage gradient along the axis of the cathode ray tube, from the cathode tothe first anode, is made to vary, the arrangement being such that the voltage gradient is relatively low at the region where the electrons pass through the aperture in the control grid, thereby permitting of complete control of the ray |by an input voltage substantially lower than has been possible heretofore.

More particularly. in accordance with my invention, an auxiliary anode, in the form of an apertured shield maintained at a positive potential substantially below that of the anode of the electron projector, is interposed between this anode and the control grid of the projector.

My invention resides in the features of constructions, proportionment, arrangement and combination of the character hereinafter described and claimed.

For the purpose of illustrating my invention, an embodiment thereof is shown in the drawings, wherein Figure 1 is a diagrammatic view of a television receiving system embodying the-present improvements, one of the parts being shown on an enlarged scale in sectional elevation;

Fig. 2 is an enlarged fragmentary view, partly broken away, of the smaller end of a cathode ray tube forming part of the present improved television system;

Fig. 3 is an enlarged fragmentary view taken A from Fig. 1:

Fig. 4 is a graphical representation of the voltage gradient along the axis of cathode ray apparatus constructed and operated in accordance with my invention;

Fig. 5 is a view similar to Fig. 3, showing a modiiication; Y

Fig. 6 is a section taken on the line 8--8 in Fig. 5;

Fig. 'l is a view similar to Fig. 3, showing another modification;

Fig. 8 is a graphical representation of characteristics of. operation of cathode ray'apparatus constructed and operated in-accordance with my invention; and Y Fig. 9 is a diagrammatic, fragmentary view, showing a modification.

With reference to Fig. 1, the cathode ray tube I is provided at the smaller end thereof with an electron projector of the general type disclosed in my copending application referred to, and in-' cluding a cathode II anda heating filament I2 therefor, an anode I3, and a control grid I4 lnterposed between the cathode and the anode.

The anode I3 of the electron projector is commonly referred to as the rst anode rof the cathode ray tube.

The filament is supplied with heating current by a battery I under control of an adjustable resistance I6.

For the purpose of controlling the intensity of the cathode ray in accordance with the received picture impulses, the grid I4 is'connected' by a lead I1 to an output lead I8 from a suitable filter I9 effective to lter out the picture impulses from a receiver 20 which includes a radio-frequency amplifier of usual type. The other output lead 2| of the iilter terminates, as shown, at an adjustable contact 22 of a resistance 23 connected acrossa battery 24. By adjusting the contact 22, the relation between the potentials on the cathode I I and grid I4V may be varied to suit particualr requirements.

It will be understood that the picture signals are transmitted on avcarrier wave at a suitable frequency, and that the synchronizing impulses are transmitted with the picture frequencies on a carrier wave-at a frequency beyond the band of picture frequencies. The filter I3 is a high-pass illter adjusted to pass to the filter 33 only the carrier wave modulated by the horizontal and vertical synchronizing impulses. 'I'he picture signals and the carrier wave modulated by the synchronizing impulses at 16 and 1,000 cycles, for example, are impressed across the resistance 3I by the connections I8 and 2I from the filter I3. The carrier wave modulated by the synchronizing impulses is demodulated in the usual manner by a demodulator which may be considered as being associated with the filter 33. The horizontal and vertical frequencies are then filtered one from the other by the filter 33 and utilized to synchronize the usual generators of saw-tooth current waves, which may also be considered as being associated with the lter 33. This part of the receiving system per se forms no part of my present invention, and is disclosed in more detail in my copending application referred to.

The resistance 24a connected across a battery 25 is provided with an adjustable contact 28 connected to the anode I3 by the connection 21, the contact being adjusted to impress the desired positive potential on the anode.

The tube III is provided with a second anode in the form of a silver or other metallic coating 28 on the interior of the tube?. 'I'he second anode 23 operates to accelerate the electrons in their movement from the first anode I3 to the screen 23, and, also, causes the electrons to come to a application, Serial No. 484,309, iiled September.

25, 1930, now U. S. Patent No. 1,955,899.

Coming now more particularly to the structural and electrical characteristics of my im- Y 1 proved system to which are attributed the advantages referred to overythe various systems proposed heretofore, reference is made to Figs. 2 and 3. An auxiliary anode, in the form of an apertured disc or shield 38, is interposed between the grid I4 and the rst anode I3, and is supported and insulated from the grid by a plurality of wires 39 having their adjacent ends connected by glass beads 40, the other ends of these wires being connected respectively to the grid and shield by spot-welding, or in any other suitable manner. The iirst anode I3 is also supported from the grid I4, and is insulated from and held in spaced' relation to the shield 38 by wires 4I having their adjacent ends connected by glass beads 42, the other ends of these wires being spot-Welded to the shield and rst anode, respectively.

The assembly, comprising the grid I4, the first anode I3, and the shield or auxiliary anode 38, is supported from the press 43 by wires 44 and 45 secured to the grid in any suitable manner such as by spot-welding. The wire 44 extends entirely through the press 43, as shown, for convenient connection with the lead Il.

In like manner, the cathode II is supported from the press 43 by the wire 45a extending through the latter for connection with the lead `48.

'Ihe heating filament is connected across and supported from the adjacent ends of the wires 41 'and 48, which also extend through the press 43 for connection with the leads to the battery I and the resistance I6.

Connection is made with the anode I3 bythe wire 43, which may be spot-welded thereto at the point 49a, which wire extends through a glass or other suitable insulating tube 50, and thence outwardly through the end wall of the tube I0 for connection with the lead 21 to the adjustable resistance contact 26. The insulating tube 50 extends through a suitable aperture in the shield 38, and operates to insulate the anode connection 49, which is at a relatively high potential, from the shield 38 and grid I4 which are at relatively low potentials.

A skirt or protective shield, in the form of a tube 52 of nickel or other suitable material, may be placed over that portion of the glass tube 53 on the grid side of the auxiliary anode 38, and may be welded or otherwise secured to this anode.

The shield or auxiliary anode 38 is connected to the positive side of a battery or other direct current source 53 by a lead 54 connected to a wire 55 extending through theend wall of the tube and spot-welded or otherwise electrically connected to this anode at a point 56.

In a television receiving system embodying the present improvements, and with which are obtained the advantages referred to, the diameter of the grid aperture 51 is approximately .085 inch, and the diameter of the auxiliary anode aperture 58 and the first anode apertures 59 is approximately .055 inch. In this system, the distance between the grid I4 and the auxiliary anode 38 is approximately .03 inch, the distance between the auxiliary anode 38 and the first anode I3 is approximately '.09 inch, and the inside diameter of the small end of the tube III is approximately two inches. While these various dimensions are found to provide for satisfactory operation, it is to be understood that the same'are not critical in any strict sense of the word, and may be varied within wide limits to suit different conditions.

In the system referred to, the battery 30 is such as to place the second anode 28 at a positive potential of 4,000 volts, the contact 26 is adjusted to place the iirst anode I3 at a positive potential of 1,000 volts, and the battery 53 is such as to place the shield or auxiliary anode 38 at a positive potential of 45 volts. With this arrangement or adjustment, a negative potential of approximately 3.5 volts is effective to completely cut oi the ray. l

In explaining the operating principle of my present improved system, reference is made to Fig. 4, wherein the values of accelerating voltage on the cathode beam are plotted against distance along the axis of the tube from the cathode II to the first anode I3. With the cathode II at zero potential, and the shield or auxiliary anode 38 at a positive potential of 45 volts, the voltage gradient along the axis of the tube at the region where the electrons pass through the aperture 51 in the control grid I4, at which region the electrons will be under the controlling influence of the grid, is expressed as At this relatively low voltage gradient, the ray intensity can be completely controlled by an A. C. input voltage of approximately 2 volts.

After the electrons pass through and beyond the controlling iniiuence of the grid I4, and reach the shield or auxiliary anode 38, the voltage gradient, which is expressed as increases sharply to a relatively high value asa result of the relatively great diilerence in potential between the shield and the iirst anode I3.

' Beyond the first anode I3, the voltage gradient is increased still further by reason of the high positive potential of 4,000 volts on the second anode 28.

From the foregoing it will be seen that the voltage gradient along the axis of the tube is Increased in steps between the cathode II and the first anode I3. The relatively low velocity of the electrons, corresponding to conditions under which the voltage gradient is leaves the electrons highly sensitive or responsive to control at the relatively low voltage on the grid I4, while the subsequent stepping up of the velocity of the electrons causes them to strike the fluorescent screen 29 at a tremendous velocity, the force of the ixpact being so high that the light or luminescence produced is ample for the development of an image of suiiicient brilliancy.

Assuming that the shield or auxiliary anode 38 is ineffective or removed from the tube structure, it will be apparent from Fig. 4 that the voltage gradient along the axis of the tube between the cathode II and the lrst anode I3 will be constant and represented by the slope a of the broken line AB. Other conditions remaining the same in the. system referredto, it will now require a negative potential as high as 35 volts to completely cut off the ray, and an A. C. input potential of about 1'2 volts to completely control the ray. For the purpose of obtaining this relatively high control voltage, it would be necessary to employ in the receiving system a high-gain audio ampliiier, as heretofore.

Without the shield or auxiliary anode 38,

therefore, the ratio of the first anode potential of 1,000 volts to the negative potential of approximately 35 volts on the control grid I4 for complete cut-off of the beam, is about 29, whereas this ratio in my present improved system, employing the shield 38, is substantially greater, and equal to or about 286. It is the relatively high value of this ratio in my present improved system which permits of satisfactory control of the beam intensity with a relatively low input voltage.

In this connection, I believe myself to be -the iirst to provide a television receiving system of the character described wherein the ratio of the operating electrical potential on the first anode I3 to the negative potential on the grid for complete cut-off of the beam, is at least 35, or between and 500.

Considering the operating characteristics of my present improved system from another aspect, I believe myself to be the first to provide a television receiving system of the character described wherein complete control of the ray is obtained by input voltages within the range of from 2 volts to 10 volts.

While dennite values of potential on the control grid and the anodes I3, 28 and 38 have been given, it is to be understood that this has been done only ior the purpose ot teaching the art operating conditions in a television receiving system constructed and adjusted in accordance with my invention, and not with the intention ot limiting myself in the appended claims to these particular values. On the contrary, it is contemplated to vary these values of potential within wide limits to suit different operating conditions and requirements.

In the modification shown in Figs. and 6, the anode Ila, corresponding to the anode I3 in Figs. 2 and 3, has an apertured base element 60 arranged transversely of the direction of travel of the ray and extending outwardly, as shown, beyond the body portion oi the anode into close proximity to the interior wall of the tube. The anode i3d-6I! is supported from the control grid Il by the wires 8| having their adjacent ends connected by the glass beads 62. The shield 38a, corresponding to the shield 38 in Figs. 2 and 3, is supported from the grid Il by the wires 63 and the interposed glass beads 84, and is of substantially smaller diameter than the anode base 80. l

This construction permits of direct connection of the anode lead 48 with the outer edge portion of the base A811, without the necessity of this lead passing through and being insulated from the shield 38a, as in Figs. 2 and 3. It is to be noted that the wires GI and the associated glass beads l2 for supporting the anode element 60 from the grid I4, are disposed entirely on the cathode side of this element. This construction eliminates the possibility of such supporting means interfering with focusing oi the electrons to a small spot on the screen 28.

'I'he construction in Fig. 7 is substantially the same as that in Figs. 5 and 6, except that the shield 38h corresponding to the shield 38a, is of the same diameter as the anode base 60. The anode is secured to the shield 38h by bolts 65 and 68 which pass through an interposed spacing ring 81 of soapstone or other suitable insulating material. The anode lead 48 in this construction may be connected to the bolt 65, and the lead 55 to the shield 38h may be connected to the bolt 86, for which purpose the bolt 65 is in electrical contact with the base 60 and insulated from the shield 38h, while the bolt 65 is in electrical contact with the shield and insulated from the base l0.

It is to be noted that in the construction shown in Figs. 2 and 3, the shield 38 has a diameter only slightly less than that of the neck of the tube I0, so that the shield extends well out beyond the anode I3 into close proximity to the wall of the tube. This construction is believedto contribute materially toward more eillcient shielding of the anode I3 by the shield 38, which appears to` give the tube such desirable characteristics that the same can function as its own detector when embodied in a television receiving system as shown in Fig. 1.

With reference more particularly to the wide range of voltages possible on the control grid I4, the first anode I3, the second anode 28, and the shield or auxiliary anode 38, Fig. 8 shows the characteristics oi. a cathode ray tube constructed in accordance with my present invention, and which is identied as No. 187. In-this ligure, the curves 88, 88, 10, 1I and 12 were obtained by plotting on the vertical axis the current in the connection 13 from the second anode 28, and by plotting on the horizontal axis the D. C. polarizing voltage on the grid Il. The curves 88 to 12 show the characteristics of the tube with the potentials Es ci' the shield or auxiliary anode I8 at 50, 70, 80, 90 and 120 volts, respectively.

During the tests made for the purpose ot obtaining the necessary data for these characterr istie curves, the resistance I8 was adjusted so that the supply voltage Ef for the filament was 2.5 volts, under which condition the filament current If was 2.22 amperes. The potential EA: on the rst anode i3 was 600 volts, and the pogsntial EA: on the second anode 28 was 2,400 vo With the shield potential' Es at "l0 volts, the D. C. polarizing voltage on the control grid Il was round to be best. for this particular tube, at about 1.5 to 2.0 volts, as indicated by the grid voltage line 14. Under these conditions. the voltage variation on the control grid for complete control oi'` the beam, would lie approximately within the range from 1 volt positive to 4.5 volts negative.

With the shield potential Es at 110 volts, the

bias on the control grid I4, for this particular tube, was found to be best at about 5 volts. Under these conditions, the voltage variation on the control grid for complete control oi' the beam, would lie approximately within the range from zero to 10 volts negative.

With the shield potential Es above 110 volts. for example at 120 volts, as shown by the curve 12, the maximum illumination of the screen 2! was less than the villumination at conditions as represented, for example, by the curves 88, 1l and 1I, and corresponded to a second anode current of about 6.6 microamperes.

The reason for this is due to the fact that, with the shield potential as high as 120 volts, there is only a relatively small increase in the second anode current during the periods oi time the gridv I4 swings in a positive direction, because the limit of electron emission from the cathode has been reached. This phenomenon is illustrated by the curve 12, from which it will be seen that at a grid potential of about 2.0 volts negative, the curve bends sharply into an almost horizontal slope. On the other hand, it will be seen from the curves 69, 10, and 1I, for example, that for lower values of shield potential, the slope of the characteristic curve is relatively sharp throughout the entire operating range of the grid voltage variation.

The data obtained in the tests referred to indicates that for the particular tube tested, having approximately the dimensions given above, most emcient operation is to be obtained by an adjustment or. arrangement whereat the potential on the shield or auxiliary anode 38 is 100 volts, andthe bias on the control grid Il at about 4 to 6 volts negative, with a variation in the picture impulse potential within a range of 8 to 10 volts for complete control of the beam. Under these conditions, the cathode ray apparatus operates on the straight-line portion of the curve, and, accordingly, functions as an amplifier, in which case a suitable detector is interposed between the R.. F. ampliiler and the apparatus Il to rectify the picture modulations on the carrier wav On the other hand, it will be seen from the characteristic curves of Fig. 8 that i1.' the grid bias is so selected thatA the lower bend oi the curve is utilized, rectification, due to assymetric conduction, will take place in the control grid circuit. This inherent rectifying action places the desired signal voltage upon 'the control grid in a manner identical to that of an external detector. The control grid I4 is then connected directly to the output of the R. F. amplifier, no external detector being required. That is, the connections I8 and 2I would connect directly with the connections shown between the receiver Ilv and the filter I9.

The degree of brightness, and character, generally, of pic-tures received with cathode ray apparatus constructed in accordance with my present invention is substantially better than the degree of brightness and general character of the pictures received with such apparatus constructed heretofore. This is partly attributed to the effect or influence of the shield or auxiliary anode in substantially eliminating electron leakage between the cathode and second anode. The shield or auxiliary anode in the present improved construction, therefore, assures substantially maximum efficiency in the way of complete utilization of the electrons for the purpose of impact with the fluorescent screen 29 to develop the light image.

An important function of the shield 38 is that substantially all of the lines of electrostatic strain, which would otherwise exist between the grid I4 and the anode I3 under operating conditions, terminate on the shield, which is at substantially ground potential for alternating current. This shield 38, therefore, substantially eliminates capacity coupling between the grid and anode, so that any effective impedance appearing in the first anode circuit will not be reflected into the control grid circuit of the tube I0. Therefore, when my improved cathode ray tube is used in place of a detector following the 40 R. F. amplifier, the shield 38 prevents the effect of increased input capacitance due to reflected plate impedance, which would otherwise occur.

Furthermore, when a radio-frequency circuit feeds the tube I0, the overall gain from the antenna to the control grid I4 is considerably greater than would be the case if shield 38 were not present.

Fig. 9 shows a modification of the systeminFig. 1 in which the cathode ray tube not only functions as its own detector of the picture impulses, but also simultaneously detects the synchronizing impulses for the defiecting coils 34 and 36. For this purpose, the bias on the grid I4 is such that the tube operates on the lower bend of the characteristic curve. No external detector is required. 'Ihe filter I9 is omitted, and the leads I8 and 2| connected directly to the R. F. amplifier contained in receiver 20. A resistor 15, shunted by a suitable by-pass capacitor 11, is connected as shown in the return lead 21 from the first anode I3. The two leads 32, previously connected to the filter I9, are now connected to the leads 16 from the ends of resistor 15. With these modifications of the system in Fig. 1, the detected picture and synchronizing impulses appear across the resistor 15. The capacitor 11 permits the relatively high frequency picture impulses to pass to the grid I'4, while the synchronizing impulses at 16 and 1,000 cycles, respectively, are fed to 'the filter 33 by way of the leads 16.

In manufacturing the cathode ray tube, the ray-projector assembly, before insertion into the open neck of the tube I0, includes the base portion 18 provided with a flange or rim 19 extending radially outwardly therefrom. After insertion of this assembly into the open neck of the tube, the edges of the rim 19 and the neck of the tube are fused' together, the line of connection being indicated by the broken line in Fig. 2. The tube is then highly evacuated and sealed o.

By the term ray cut-off, is meant the condition at which the electron ray is so diminished that no spot of light is perceptible on the screen structure 29.

Having described my invention, what I claim 1. A cathode ray tube comprising an electron gun having an electron emitting element, an

apertured control electrode and an aperturedfirst anode, each positioned in axial alignment and longitudinally spaced one from the other, a target member supported in the opposite end of the tube from said electron gun assembly, and an apertured shielding electrode positioned intermediate the control electrode and the anode, said shielding electrode extending transversely beyond the transverse extremities of each of said control electrode and said anode and a second anode intermediate the first anode and the target.

2. A cathode ray tube having an envelope, including at one end thereof, an electron gun assembly comprising an electron emitting cathode, an apertured control electrode, and an apertured first anode, each of said elements being positioned in axial alignment and progressively spaced from each other in a longitudinal direction, a target member positioned substantially at the end of the envelope opposite the electron gun, a second anode intermediate the first anode, and the target and an auxiliary shielding electrode interposed between the control electrode and the anode, said shielding electrode having an aperture axially aligned with the apertured control electrode and anode, and said shielding electrode extending transversely of the tube substantially to the tube wall. Y

3. A cathode ray tube comprising an envelope having a necked portion, wherein is supported an electron gun assembly, said electron gun assembly comprising an electron emitting cathode, a control electrode having an aperture through which the emitted electrons pass, and a first anode electrode also having an aperture axially aligned with the control electrode aperture and longitudinally spaced from said control electrode and said electron emitting cathode, whereby upon i the application of suitable voltages between the said anode and cathode an electron beam is developed, a target member supported in the opposite end of the envelope for receiving the developed electron beam, a second anode intermediate the first anode and the target, and a shielding electrode positioned between the control electrode and the first anode, said shielding electrode being of disk formation and extending substantially transverse of the necked porion of the tube and substantially to the tube wall, said shielding electrode also having an aperture axially aligned with the apertures of the control electrode and the anode.

4. An electron tube comprising an enclosing envelope having a stem. member at one end thereof, a plurality of support members secured Within the stern portion of the envelope and protruding inwardly of the envelope, a cold electrode member supportedrigidly from the inwardly extending support members and a cathode member also positioned within said envelope and at least partially surrounded by the rigidly supported cold electrode, and a plurality of additional cold electrodes rigidly supported from the rst named Y cold electrode independently of the support stem and in coaxial relationship with the first named electrode and the cathode.

5. An electron tube comprising an enclosing envelope having a stem member at one end thereof, a plurality of support members secured to the stem portion of the envelope and protruding inwardly of the envelope, a cold electrode member supported rigidly from the inwardly extending support members and a cathode member also positioned within said envelope and at least par- 15 tially surrounded by the rigidly supported cold electrode, and a plurality of additional cold electrodes rigidly supported from the first named cold electrode independently of the support member and in coaxial relationship with the first named electrodeand the cathode.

Q 6. The method of adjusting the preliminary concentration of an accelerated bundle of cathode rays to be afterwards focussed to produce an electron image in a receiving plane, more particularly in a television tube, by adJusting independently from the subsequent focussing, the speed to which the electrons forming the bundle are rst accelerated.

VLADMR K. ZWORYKIN.

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