US1993468A - Device for preventing variation in the speed of the electrons in the case of braun tubes - Google Patents

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5 M. VON ARDENNE v 393,468 DIQVIUE FUR PREVENTING VARIATION IN THE SPEED UP THE ELECTRONS IN THE CASE OF BRAUN TUBES Filed NOV- 25, 1931 der) surrounding the same.

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Monte -5 2 DEVICE FOR. PREVENTING VARIATION IN THE SPEED OF THE ELECTRONS IN THE CASE OF BRAUN TUBES Manfred von Ardenne, Berlin, Germany, assignor to Radioaktiengesellscliaft D. S. Loewe, Berlin- Steglitz, Germany, a company of Germany Application November 23, 1931, Serial No. 516,849 In Germany November 22, 1936 "5 Claims.

(Granted under the provisions of sec. 14, act or March 2, 1927;357 0. G. 5)

Various methods are known for controlling the intensity of light in the case of Braun tubes, such are preferably employed for television purposes. Among these methods the one would appear to be very hopeful, in which the intensity of the rays is varied by an alternating potential between the cathode and a cylinder (Wehnelt cylin- In place of the Wehnelt cylinder it is naturally also possible to employ other elements of control, such for example as grids. When performing control through the medium of elements of this nature it has been shown that the light intensity of the fluorescent point may be reduced down to very small amounts, without in the case of electro-statically deflected rays appreciable displacement of the point taking place by reason of considerable variations in speed. By the use of control electrodes of this nature, in which the control field is substantially transverse to the field of acceleration of the anode, and more particularly, therefore, when employing cylindrical electrodes, such for example as the Wehnelt cylinder, it may be accomplished that the concentration of the rays may also be well maintained. By reason of the cylinder or grid potential the form of the charge cloud surrounding the cathode, and accordingly the eflective cathode surface, is varied.

A certain it only a very small efiect on the speed of the electrons preventing proper utilization of the fundamentally existing possibilities of the Braun tube nevertheless remains. The extent of the variation in speed in the case of control between light and dark is approximately between 5 and 10%. As to be expected theoretically, the direction is also such that in the case of a strong negative bias potential, i. e., when approaching the extreme state dark the speed of the electrons diminishes. This according to the inventin may be prevented in simple manner by causing'the anode potential to fluctuate with corresponding amplitude in counter-phase to the fluctuations in intensity.

The variation in speed may in practice be compensated in very simple fashion for a lengthy and, generally speaking, undoubtedly sufllcient interval in the intensity. If a purely ohmic resistance is included in the anode circuit, it is accomplished that at the moments of considerable ray currents, i. e., of great intensity, due to the increased potential spacing, which increases simultaneously with increasing anode current, a smaller anode, potential exists than at the moments of weaker currents.

The mug iavourable value for the resistance may be discovered in very simple fashion by the fact that when passing the potential to the intensity control the resistance is brought to that value at which, in deflected state, the point or edge of the image appears with optimal sharpness. Experiments have shown that the most favourable value for the resistance when employing the tubes produced by the applicant was situated in the order of 10 ohms. i

A form of embodiment of the invention is illusm trated in the drawing. In the latter, 1 is a Braun tube having the cathode 2, the anode 3, the Wehnelt cylinder 4 and the deflecting plates 5. The cathode is heated by a battery 6, while the necessary negative bias potential is conducted to 5 the Wehnelt cylinder from the grid battery '7 over the secondary coil 8 of the control transformer 9. The potential for controlling the intensity. of light is applied to'the terminals 10 of the primary coil 11 of the control transformer 9. 20 The anode potential is supplied by the battery 12, which is connected with the anode 3 over the resistance 13 according to the invention.

I claim:

1. In a television arrangement a Braun tube gs having a cathode for generating a cathode ray, an anode, a picture screen, means for deflecting said cathode ray and means for controlling the intensity of said cathode ray, means for generating an anode, a picture screen, means for deflecting 40 said cathode ray, and means for. controlling the intensity oi. said cathode ray, means for generating deflecting voltages controlling said deflecting means, means ior generating a control voltage controlling said intensity controlling means, 45 and means for compensating the disturbing varia; tions in velocity of said cathode ray resulting from the intensity control thereof, said compensating means varying the anode potential in counterphase to said disturbing variations, and'compris- .50

ing a resistance in the anode circuit.

3. In a television arrangement a Braun tube having a cathode for generating a cathode ray, an. anode, a picture screen, means for deflecting said cathode ray, and means for controlling the in- 56 tensity of said cathode ray, means for generating deflecting voltages controlling said deflecting means, means for generating a control voltage controlling said intensity controlling means, and means for compensating the disturbing variations in velocity of said cathode ray resulting from the intensity control thereof, said compensating means varying the anode potential in counterphase to said disturbing variations, and compristhe anode potential in counter-phase to said disturbing variations, and comprising a resistance in the order of 10 ohms in the anode circuit.

5. In a television arrangement a Braun tube having a cathode for generating a cathode ray, an anode, a picture screen, means for deflecting said cathode ray, and means for controlling the intensity of said cathode ray, means for generating deflecting voltages controlling said deflecting means, means for generating a control voltage controlling said intensity controlling means, and means for compensating the'disturbing variations in velocity of said cathode ray resulting from the intensity control thereof, said compensating means varying the anode potential in counterphase to said disturbing variations, and comprising a resistance in the anode circuit, the optimal value of said resistance being acflusted by obtaining optimal sharpness of the fluorescent point upon deflection.

' MANFRED vou ARDENNE.

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