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In an HCR-Tube, the deflecting system used to deviate the electron beam is made of positively charged plates. How is this justified? If, due to some malfunction, the electron beam deflects from its original path before it is actually supposed to, won't it stick to the plates? And why is it not wiser to use negatively charged plates? If this is done, then the electrons of the beam will return to their stream even if they are accidentally deflected, and when the actual deflection is required positive plates can be introduced.
So why only positive plates?

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As far as I know, in the CRTs used in (old) TVs and computer screens the beam is deflected using magnetic fields. Where very high frequency deflections are required, e.g. in oscilloscopes, a pair of charged plates are used, one positive one negative, to produce an electric field gradient that deflects the beam. Do you have a reference for a CRT using just positively charged plates? –  John Rennie Nov 13 '12 at 10:22
In the type of tube you're talking about, with the steering accomplished by electric rather than magnetic forces, there would be a pair of oppositely charged capacitor plates. The beam flies between them and is attracted to the + and repelled by the -. Electric circuits are basically always electrically neutral as a whole. –  Ben Crowell Apr 13 '13 at 1:32

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