US2178775A - Means of eliminating interference caused by induction in electron tubes - Google Patents

Description

w. BUNGER El AL MEANS OF ELIMINA'I'INE IFNTERFERENCE CAUSED BY INDUCTION IN ELECTRON TUBES Nov. 7, 1939.

Filed July '23, 1937 2 Sheets-Sheet l grime/M900 anm Nov. 7, 1939- w. BUNGER sf AL 2.178.775

MEANS OF ELIMINATING INTERFERENCE CAUSED BY INDUCTION IN ELECTRON TUBES Filed July 25, 1937 I 2 Sheets-Sheet 2 I II! +4 All II W ww a. I m

Patented Nov. 7, 1939 MEANS OF ELIMINATING INTERFERENCE CAUSED BY INDUCTION IN ELECTRON TUBES Walter Biinger, Berlin-Zehlendorf, and Hans- Wolfgang Langenwalter, Klein-Machnow, Germany, assignors to the firm Fernseh A. G., Zehlendorf, near Berlin, Germany Application July 23,'1937. Serial No. 155.322 In Germany August 8, 1936 3 cams- (obese-21) This invention relates to screens "for meansfof eliminating interference caused by induction in electron tubes, and leads coming to and from such tubes; In particular this invention relates to the elimination of interference in tubes in which the leads are brought in through a plurality of projections.

Examples of such tubes are picture transmitting tubes ior television purposes with-built-in electron multiplier systems in which an optical image is focused upon a photosensitive cathode. The electrons liberated from the photo-cathode are focused. in image relation by electrical or magnetic means in a plane in which a scanning aperture of the size of a picture element is disposed which allows the electrons constituting the signal corresponding to one picture element to fall upon a target or into an electron multiplier system. Variable magnetic transverse fields have the effect that electrons from all picture elements come to an electron collector in a successive order.

The varying magnetic fields inductively afiect the collector and the leads to the electron multiplier system. Especially when an electron multiplier system is employed which necessitates a number of potential leads, these interferences may become so great that the television image becomes fiat or is entirely covered by interference 80 noise.

According to the invention shielding means are provided, particularly inner and outer screens, whereby the inner screen is connected with the 35 outer screens located at every projection which contains leads to be screened. The outer screensleading from the projection are connected only to the inner screen and both are isolated from ground. Only in such an arrangement complete elimination of interference is achieved, whereas for instance the earthing of the exterior screen in one or several places does not render the desired result. The described manner of interference is possible in all kinds of magnetic interfering fields. Not only the deflecting fields but also, for instance, alternating fields created by power mains are often the cause of interference,

and their detrimental effect may be eliminated in the described method.

Fig. 1 shows a schematic diagram, partially in section, of an image dissector tube connected to an amplifier and a voltage divider.

Fig. 2 shows a schematic sectional diagram of a modification of the invention, wherein a T- shaped shielding element is provided.

Fig. 3 shows a modification of the means for grounding the inner shielding devices. I

The picture analyzer tube l of Fig. l contains a photosensitive cathode 2 and an anode 3, whereas the deflecting coils 4 are disposed outside 5 of the tube. The magnetic fields of these coils which are necessary for deflection have an interfering effect upon the leads to the signal electrode and to the electron multiplier in the tube.

The signal electrode not shown in the drawings lies behind the scanning aperture 5 of a screening cylinder 6. The lead I, which is connected to the signal electrode (not shown), is brought out through an extended seal 8 on one side of the tube, to an amplifier. Outside of the tube thelead is screened by a cylinder 9 which is directly connected with a cylinder 6 through the glass wall and protrudes over the cylinder 6. 'The screen 9 of the signal lead is connected with the screening case 40, of the amplifier, the first tube go I0 of which is schematically indicated. The cathode of the tube I0 is connected to the case 40 atapointll.

On the other side of the tube are, for instance,

three voltage leads l2, l3, and I4, which are'connected to the electron multiplier, not shown on the drawings, and which are brought in through an extrusion l5. The leads are screened off by the cylinder 16, which is connected to the inner cylinder 6 through a second sealed-in lead ll. 3 The cylinder I6 is connected to a case l8 in which the voltage leads l2, I3 and [4 are connected to the case through the condensers I9, 20, 2|. The leads are connected through the resistances 22, 23 and 24 to a voltage divider, which maybe grounded in some suitable manner, whereas all other screening parts must be isolated. A ground connection on any other spot, for instance, on the cylinders 9 or IE, leads toheavy interferences. If the amplifier I0 is a preamplifier, the connections of which with the main amplifier must also be screened, it is advisable to use the circuit shown in Fig. l. The plate and filament voltage is brought in through a screened cable 4|. Parallel and in close proximity a sec- 0nd screen cable 42 is disposed which contains the modulation lead. The plate and filament voltage leads are connected with the case 40 through the condensers 38 and 39. The case of the main amplifier is grounded at 43 whereas all other screens are isolated.

As many voltage leads as desirable may be brought into the electron multiplier if they are picture analyzing tube whereby this cross section shows an arrangement with three projections.

The inner screen has the form of a T-shaped case 25. The outer screens 26, 21 and 28 are connected with the inner screen through the sealed-in leads 29, 30 and 3| and are not permitted to touch I each other outside of the tube. The signal electrode is brought out through one arm of the T- shaped case, whereas the voltage leads 32, 33, 34 and 35 go through the two other arms. The connection of these leads to the screen by means of condensers is made in the same manner as-shown in Fig. I. The four voltage leads go to the same potentiometer 36 which may be connected to ground as may seem suitable.

. .Insome cases it may be advisable to connect the entire screening system in the interior of the tube through a capacity 31 to the outer screen which is connected to ground and to apply by way. of a resistance a voltage to the end of the other branch of the outer screening. The condenser 31 may be shunted by a resistor 31 as is shown in Fig. 3.

The arrangement is not limited to the picture analyzing tubes shown in, the drawings. This invention may be applied in all cases of high frequency work where inductive interferences are to be eliminated and where it is to be prevented that screens should form a loop in a magnetic field.

We claim: 1. In combination with a television transmitting tube, means for shielding signal carrying .leads from potential carrying leads comprising a plurality of extruded portions formed on said tube, potential leads and signal leads disposed separately through said extrusions and sealed therein, inner shielding means surrounding said leads and extending into said extruded portions of said tube, external shielding members individually associated with said signal and potential carrying leads. and means for connecting each of said external shielding means separately to said "internal shielding means and means for grounding said external shielding means.

2. The combination of a television transmitting tube and a shielding device substantially as described in claim 1, wherein said signal and potential leads are capacitatively connected to said external shielding means. LS3. A device substantially as described in claim lgwherein said potential leads are connected to a voltage dividing device, said voltage dividing device being grounded.

WALTER Bl lNGER. HANS-WOLFGANG LANGENWALTER.

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