US2563490A - Cathode arrangement fob television - Google Patents

Description

Aug. 7, 1951 R. R. THALNER cATHoDE ARRANGEMmn FOR TELEVISION TUBES Filed Jan. 28, 1946 .Iliff Iliff 1 f l 1 l l 7.

INVENTOR Rabe/711?. 72H/nez UNITED STATES PATENT OFFICE CATHODE ARRANGEMENT FOR TELEVISION TUBES Robert R. Thalner, Princeton, N. J., assignox to Radio Corporation of America, a. corporation of Delaware Application January Z8, 1946, Serial No. 643,927

Claims.

This invention relates to television tubes of the image orthicon type, such as is disclosed in the application of Paul K. Weimer, filed September 16, 1944, Serial No. 554 494, now U. S. Patent 2,433,941, issued January 6, 1948, but it is not 5 wards the rear of the tube is an electron mirror limited thereto. Il consisting of an electrode having about the In the image orth'icon of the construction same potential as the cathode, namely, ground, shown in said application, the light from the as illustrated in the drawing, or a more negative thermo-active surface of the gun cathode is propotential, for suitable reflection of the electrons. jected onto the photocathode through the glass lf The grid IIJ in this case may be connected to target and produces an effect comparable with ground through a positive bias source I8 to prothat of the image projected thereon from the obvide an accelerating field for urging the electrons ject being televised, particularly at low illuminareflected from mirror electrode I'I through the tion of such object. tubular cathode I3 and along the beam path to- It is an object of this invention to arrange the l5 ward the target electrode 4. Between the anode cathode so the electrons therefrom can be pro- 'I and the decelerating lens 6 a wall coating I9 jected through the grid aperture without the is located on the inside of the envelope. Adjalight reaching such aperture. cent the dynode S is positioned a persuader elec- Another object is to face the cathode surface trode for directing the secondary electrons away from the aperture in the grid toward an 0 into the remaining dyncdes and associated parts electron mirror, which reilects the electrons, but indicated at 9. The magnetic deflection unit 2l not the light from the cathode, through the apercontaining the vertical and the horizontal deture. ection coils is placed outside the envelope. Other objects will appear in the following spec- Longitudinal adjustment of this coil may be made ication, reference being had to the drawings, in by manipulation of rod 2I'. These coils are not which; individually, shown, as they are of the usual con- Fig. 1 is a cathode beam tube embodying my struction and their action is well understood. invention. Coil 22 is adapted to be manually adjusted Fig. 2 is a modification of the construction of around the axis of the tube to compensate for Fig. 1. slight misalignment of the beam. Outside of Referring to Fig. 1 of the drawing, an image these two units is placed the electromagnetic foorthicon such as disclosed in said application of cusing coil 23 for focusing the photo-electrons Paul K. Weimer is modied so as to embody my and the beam electrons, as well understood. invention, but by way of example only. The The glass target 4, which Iis translucent, is cathode beam tube consists of an envelope I mounted in a metallic frame 24 containing the having a photocathode 2. electrode 3, glass tarcollecting screen 5 and this frame is grounded. get 4 and collecting screen 5 for producing a The decelerating lens 6 is grounded, but it may charge imageon the glass target. On the other also be given a slightly higher potential than side of the glass target from the screen 5 ispoground. Photo-electrons are emitted by the sitioned the decelerating ring or lens 6. At the photocathode 2 by action of the light image foother end of the tube is the gun comprising a cused thereon from the external object, not cathode II, a grid I0, and a first anode 'I. The shown. These are accelerated by electrode 3 rst anode. l, has a front surface 8 which conalong the field lines of the focusing coil 23 to the stitutes the first dynode of the multiplier. The glass target 4 through the screen 5. The elecother dynodes illustrated in said Weimer applitrode 3 is made more negative than ground. 'Ihe cation are indicated as a unit 9 and are not horizontal and vertical deflection coils: in unit 2l shown in detail as they, per se, are not part of would be connected to the usual saw-tooth genthis invention. Inside the first anode 1 is the erator of line and frame frequencies,respectively. grid IIJ. The grid I0 and rst dynode 8 have The wall coating I9 and first anode 'I would be the usual small apertures for forming the beam. of connected to suitable positive potentials, as dis- Instead of positioning the cathode II so as to face closed in said Weimer application and as well towards the grid aperture, I reverse it so that known in the art. the incandescent and thermo-active end I2 The construction shown in Fig. l is that disfaces in the opposite direction and .is shielded closed in the application of said Paul K. Weimer, from photocathode 2 by the opaque portions of t5 except for the particular form of cathode II and the cathode II and electrodes 8 and III. This associated parts for reversing the electron flow cathode II may be constructed of two cylindriand deflecting the electrons back through the cal shells I3 and I4 joined together at one end grid aperture. by an annular wall portion having the incandes- In the operation of this tube, the incandescent cent thermo-active surface I2. 'I'he heater coil, co

2 H, is then placed in the annular space between these two cylinders. This leaves an opening I5 for passage of the electrons. Back of the cathode is located an anode screen I6 and further tosurface I2 of the cathode emits electrons which are accelerated by positive screen anode I6 away from the thermionic cathode surface I2. These electrons pass through the apertures of this screen electrode to be reflected by the electron mirror I1 and are then accelerated by anode 1 back through the screen I6, the opening inthe hollow cylinder I3 of the cathode and the grid aperture, towards the target. The beam electrons not landing on the target to discharge the charge image thereon return to the first dynode surface 8 and bombard electrons therefrom. These are directed around behind the first dynode 8 by the persuader 20 and the more positive potentials of the remaining dynode units 9 toward the deflector unit, the construction of which is shown in said Weimer application. These electrons, of course, enter the annular opening all around the anode 'I and not at one point only, as indicated in the drawing for purposes of explanation. The electrons of the returning beam also scan the surface outside the aperture of the first anode to produce the secondaries.

The electron mirror I'I does not reiiect the light from the heated end I2 of the cathode as it does not have a good light reflecting surface and hence light therefrom cannot reach the target. It therefore cannot affect the photocath- -ode 2.

In Fig. 2 I have shown a modification in which the anode accelerates the electrons fromthe rear end I2 of the cathode at such velocity as to produce secondary electrons by bombarding electrode 25, which are accelerated through the inside channel I5 of the cathode. constructed as shown in Fig. 1. The action of this modification is the same as that of Fig. 1 except that the electrons finally projected through the grid aperture are secondary instead of primary electrons.

Having described my invention, what I claim l. An electron discharge device comprising, an electron gun structure for producing an electron beam along a normal path, a photosensitive electrode positioned transversely to said electron path,

said electron gun structure including a thermionic cathode electrode having an electron emitting surface surrounding and spaced from said beam path, and means between said photosensitive electrode and said thermionic cathode surface for shielding said photosensitive electrode from light emitted by said cathode emitting surface.

2. An electron discharge device comprising, an electron gun structure for producing an electron beam along a normal path, a photosensitive electrode positioned transversely to said electron path, said electron gun structure including a thermionic cathode electrode having an annular thermionic emitting surface spaced from and coaxial to said beam path, and means between said photosensitive electrode and said thermionic cathode surface for shielding said photosensitive electrode from light emitted by said cathode emitting surface.

3. An electron discharge device comprising, an electron gun structure for producing an electron beam along a normal path, a photosensitive electrode positioned transversely to said electron path, said electron gun structure including a c ode electrode comprising a tubular member sp from and coaxial to said beam path and an annular wall portion extending radially from said tubular member, the surface of said wall portion facing away from said photosensitive electrode being thermoemissive, and means between said photosensitive electrode and said thermo-` emissive cathode surface for shielding said photosensitive electrode from light emitted by said cathode emitting surface.

4. An electron discharge device comprising, an electron gun structure for producing an electron beam along a normal path, a photosensitive electrode positioned transversely to said electron path, said electron gun structure including a cathode electrode comprising a tubular member spaced from and coaxial to said beam path and an annular wall portion extending radially from said tubular member, the surface lof said wall portion facing away from said photosensitive electrode being thermoemissive, and electrode means between said photosensitive electrode and said thermoemissive cathode surface for shielding said photosensitive electrode from light emitted by said cathode emitting surface, an electrode forming an electron mirror facing said thermoemissive cathode surface and positioned on the other side of said cathode electrode from said photosensitive electrode for reflecting electrons from said cathode along said beam path, and an accelerating electrode between said cathode and photosensitive electrode for causing the electrons reflected from said mirror electrode to pass along said beam path through said tubular cathode toward said photosensitive electrode.

5. An electron discharge device comprising, an electron gun structure for producing an electron beam along a normal path, a photosensitive electrode positioned transversely to said electron path, said electron gun structure including a cathode electrode comprising a tubular member spaced from and coaxial to said beam path and an annular wall portion extending radially from said tubular member, the surface of said wall portion facing away from said photosensitive electrode being thermoemissive, and electrode means between said photosensitive electrode and said thermoemissive cathode surface for shielding said photosensitive electrode from light emitted by said cathode emitting surface, an electrode positioned transversely to said beam path and on the other side of said cathode electrode from said photoemissive electrode, said electrode having a secondary electron emitting surface facing said thermoemissive cathode surface for receiving electrons from said cathode, and an accelerating electrode between said cathode and said secondary electron emitting electrode for causing the secondary electrons to pass along said beam path through said tubular cathode toward said photosensitive electrode.

ROBERT R. THALNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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