US2267083A

US2267083A - Arrangement comprising cathode ray tubes

Info

Publication number: US2267083A
Application number: US275393A
Authority: US
Inventors: Gier Johannes De
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1938-06-13
Filing date: 1939-05-24
Publication date: 1941-12-23
Anticipated expiration: 1958-12-23
Also published as: BE434865A; GB525601A; FR856091A

Description

Dec. 23, 1941. DE GlER I 2,267,@83 ARRANGEMENT COMPRISING CATHODE RAY TUBES Filed. May 24, 1959 v TELEVISION RECE/Vl/VG APPARATUS ATTORNEY Patented Dec. 23, 1941 STATES mean eerie ARRANGEMENT COMPRISING CATHODE RA Y TUBES poration of Delaware Application May 24, 1939, Serial No. 275,393 In Germany June 13, 1938 3 Claims.

It has already been suggested to provide a cathode ray tube with four apertured diaphragms having alternately a high and a low potential, and to apply modulation voltages to the first and to the third screen. This arrangement has the advantage that the characteristic curve of the tube may have a desired curvature but involves the disadvantage that for each electrode a special voltage connection must be available.

According to the invention the apertures of the diaphragms are chosen of different. size in the case of tubes having, at least three apertured diaphragms before the cathode, i. e., the aperture in the first diaphragm or electrode is larger than the aperture in the third diaphragm. This makes it possible to obtain a still more defined and reduced spot of light on the screen or target electrode, and, in addition, to connect these electrodes directly one with another. If a fourth apertured diaphragm or electrode is provided, this may be connected directly to the second diaphragm or electrode. In this manner two connections to the supply device are avoided. The connections are preferably arranged at the inside of the tube itself so that for the four electrodes only two terminals of the tube are to be connected to the supply device.

In view of the slope of the characteristic curve a. larger axial dimension is used for the third electrode than for the first one. It is also advantageous, if the second electrode has a larger aperture than the fourth one. However, it is preferably chosen smaller than the aperture in the first. electrode, and the aperture in the third diaphragm or electrode is at the utmost equally large as the aperture in the second electrode.

A favorable feature of the arrangement according to the invention consists in that the unavoidable voltage fluctuations in the available mains circuit affect the intensity of the cathode rays to a less extent or in case of correctly chosen voltage conditions do not affect it at all practically within wide ranges.

The invention may be used for several purposes, for example, in connection with the receiving tube of a television receiver, with tubes for the transmission of pictures and with the cathode ray oscillograph.

In devices including the modulation of the intensity of the cathode ray beam the invention entails the advantage that a particularly favorable curvature of the characteristic curve may be obtained and that at the same time a great slope is possible, an advantage which is obtained according to the invention with a very simple circuit arrangement.

The invention will be more clearly understood with reference to the attached drawing showing, by way of example, a form of construction of an arrangement according to the invention.

The cathode I is surrounded by an electrode 01' Wehnelt cylinder 2 which is connected to a point 4 at the potentiometer 5 through the resistance 3. Modulation voltages may be applied to the resistance 3. The point 4 has a negative potential of say 25 volts in regard to the point 6, to which the cathode is connected. The end wall 9 of the electrode 2 is arranged in front of the emitting surface 8 of the cathode and has an aperture ID of say 2 mm. in diameter, allowing the passage of electrons therethrough. An apertured electrode II is connected to the point I2 of the potentiometer 5. The latter has a positive potential of say -300 volts positive in regard to the cathode.

The positive electrode II, which has an aperture I3 allowing the passage of electrons of say 1.5 mm., is followed again by a negative electrode I4 which has preferably a larger axial dimension than the electrode. 9. The aperture I5 in the screen I4 is say 1 mm. in diameter. Finally a positive apertured electrode I6 is provided, the aperture ll of which has a smaller diameter than the apertures of the preceding electrodes. It'is say 0.5 mm. The electrode It may be dispensed with, if the further part of the tube I8 comprises another positive electrode, for example in the form of a conducting wall coating.

A further concentration of the cathode-ray beam may be produced also by a magnetic field.

Said arrangement of the electrode system and the above-mentioned potential division maintains the current of the cathode ray beam passing through the aperture I'I, independent within wide ranges of the voltage of the source feeding the device. This can be explained as follows: A portion of the electrons emitted by the cathode is reflected by the negative screen I4 and collected by the screen II. In case of a higher voltage at the potentiometer 5 the potential difierence between the grid 9 and the cathode I is increased, involving a decrease of the beam current. If the reflection of electrons to the electrode II increases due to the decrease of the potential at the screen I4, the potential of II and It increases to a less extent than the terminal voltage due to the voltage drop in the part of the potentiometer 5 traversed by current, or it may even decrease. In this casethedecrease of the potential of the electrode 9 is not compensated for by a higher anode voltage. The arrangement according to the invention does not show this effect; in this arrangement the deflection of electrons to the electrode II does not increase with a decrease of the potential of the electrode I4. If the aperture I3 is larger than the aperture I5, the current of electrons absorbed by the electrode ll may even decrease at a higher negative voltage of the grid Hi. If the potential of the control electrode 9 becomes more negative due to an increase of the mains voltage, the decrease in current involved is compensated for by the increase of voltage at the electrodes l I and H5 in case of correct dimensions of the electrode apertures. The feed device may therefore be constructed for a comparatively low current capacity, for the voltage drop interferes only to a small degree.

In spite of the independency of the beam current with respect to the variations of the grid voltage produced by variation of the mains voltage, the tube has a considerable slope.

In cathode ray tubes with electrostatically modulated beam current the ratio between current and modulation voltage may be expressed by the formula I=kE in which I is the current of the beam of rays and E the modulation voltage. The larger the exponent p, the more the characteristic curve of the tube is curved and the sharper becomes the picture.

With a picture film the ratio between the blackening S and the brightness B of the recorded object is given by a corresponding formula S=lB If the electrical transmission of films is concerned, the exponent p of which has a value of approximately 1.8, a Braun tube with constant slope (12:1) may be used for the projection. For the reproduction of a directly recorded picture, the tube itself has to produce the curvature of the brightness curve of the picture and p is to be given preferably the value 1.8. This may be accomplished, as is known, by providing two modulation electrods which are alternating with a positive electrode. In the known arrangement the two modulation electrodes must have different ground potential and unequally high modulation voltages. For this purpose special potentiometers and connection means are required. The invention makes the several voltages superfluous. In View of the fact that the aperture H! of the first control electrode 9 is taken larger than the aperture ii of the control electrode M, the characteristic curve is formed such that it corresponds to the desired equation at equal potential of the electrodes 9 and Id. In order to assure that the factor k is suificiently great, without increasing the internal resistance of the tube, a larger axial dimension is used for the second. modulation electrode it than for the first one 9. This electrode may be, for example, two times as thick as the electrode 9.

Besides the advantage that in the arrangement according to the invention the variation of the light intensity due to variations of voltage is only very small, the invention entails the advantage of a very good picture quality with an excellent slope.

The electrode system is surrounded by a cylindrical electrode l9. This serves for shielding the electrode system and accordingly makes the control system insensitive with respect to extraneous electric fields. It simplifies also the arrangement of the electrodes, since the positive electrodes ll and I6 may be directly connected electrically to the shield so as to permit the use of the shield at the same time as a support for the electrodes H and I6. If the distance between the electrodes is sufiiciently small, or if the outer diameters thereof are sufficiently large, the shield I9 is superfluous and may be omitted.

The electrode arrangement shown in the drawing and described above may be very advantageously applied to the image tube in a television receiving set. A television receiving apparatus is shown schematically at 29, the amplified and detected video signals being impressed across the resistance 3 in order to modulate the cathode ray beam in the manner explained above. The cathode ray beam may be appropriately deflected by electrostatic and/or electromagnetic means in order to scan the fluorescent or luminescent coating 22 on the inside surface of the enlarged end of the cathode ray tube. The intensity of the cathode ray beam as determined by the modulating potentials applied thereto, together with the systematic deflection of the beam over the fiuorescent material 22, causes a reproduction of a television image. In such devices it is highly desirable that the intensity and focus of the cathode ray beam be not affected by variations in the power supply, and the device shown and described will overcome any such variations so that the intensity of the cathode ray beam will depend solely upon the modulating potentials derived from the television receiving apparatus and not upon variations in the source of voltage supply. Furthermore, the cathode ray beam will remain in proper focus irrespective of slight changes in the voltage at the power supply by reason of the arrangement in accordance with the present invention.

It is obvious that various alterations and modifications may be made in the present invention and that the device disclosed may be used in various capacities without departing from the spirit and scope of the invention, and it is desired that any and all such modifications and usages be considered within the purview of the present invention except as limited by the hereinafter appended claims.

I claim:

1. A cathode ray tube including a source of electrons for producing a cathode ray beam and a plurality of electrodes for determining the intensity of the beam and for controlling the crosssectional area or focus of the beam, said plurality of electrodes including a first control electrode,

maintaining said control electrodes normally negative with respect to said source of electrons,

means for electrically connecting said accelerating electrodes to said tubular shield member, and means including said source of potential for maintaining said accelerating electrodes and said tubular member positive with respect to said source of electrons whereby variations in the beam current as well as the focus of the beam are unafiected by changes in the source of potential.

2. In combination with a television receiving apparatus wherein means are provided for receiving and amplifying television signals, a cathode ray tube including a cathode for producing a beam of electrons and a fluorescent or luminescent screen against which the electrons are directed, aplurality of electrodes including a first control electrode, an accelerating electrode and a second control electrode, all of said electrodes being positioned between said cathode and the screen and relatively adjacent the cathode, each of the electrodes being provided with a circular aperture, the apertures being in axial alignment and of decreasing diameter in the direction of electron beam flow, a source of potential, a potentiometer connected across said source of potential, means including said potentiometer for maintaining said control electrodes negative with respect to said cathode by a predetermined amount, a tubular member surrounding all of said electrodes for shielding said electrodes, means for connecting said tubular shield member to said accelerating electrode, means including said potentiometer for maintaining said accelerating electrode and said tubular shield member positive with respect to said cathode, and means for impressing the television signals across the control electrode and the cathode,

whereby the intensity of the cathode ray beam may be varied in accordance with the television signals, and whereby variations in the beam intensity and the focus of the beam will be independent of variations in the source of potential. 3. A cathode ray tube including a cathode for producing a cathode ray beam and a plurality of electrodes for determining the intensity of the beam and for controlling the cross-sectional area thereof, said plurality of electrodes including a first control electrode, a first accelerating electrode, a second control electrode and a second accelerating electrode, the electrodes being positioned in the order named, and the control electrodes and the accelerating electrodes being provided with axially aligned apertures of progressively decreasing size in the direction of electron beam flow, means for normally maintaining the control electrodes negative with respect to the cathode by a predetermined like amount, a tubular member surrounding all of said electrodes for shielding said electrodes, means for electrically connecting the said tubular shield member to said accelerating electrodes, and means for maintaining the accelerating electrodes and the tubular shield electrode positive with respect to the cathode by a predetermined like amount.

JOI-IANNES DE GIER.