. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. CATHODE RAY TUBE per ampere-turn in the winding. A deflector coil assembly is typically a slotted annulus of magnetic material into which the windings are recessed, which fits over the tube neck as shown in Figure The arrangement of windings may be easier to see in Plate , but here the annulus is not slotted. For other and simpler forms, consult, Cocking^. Alternatively, new slotted annuli in Ferroxcube may be obtained from Messrs Mullard Ltd. (, FX1154). Magnetic catho
. Electronic apparatus for biological research. Electronic apparatus and appliances; Biology -- Research. CATHODE RAY TUBE per ampere-turn in the winding. A deflector coil assembly is typically a slotted annulus of magnetic material into which the windings are recessed, which fits over the tube neck as shown in Figure The arrangement of windings may be easier to see in Plate , but here the annulus is not slotted. For other and simpler forms, consult, Cocking^. Alternatively, new slotted annuli in Ferroxcube may be obtained from Messrs Mullard Ltd. (, FX1154). Magnetic cathode ray tubes proper are singularly free from faults; most of the display distortions are caused by imperfections in the deflector coil assembly. An important tube fault is: Biaxial pin-cushioning (Figure ). A given deflector coil current produces a certain beam deflection angle {of. tangent of angle in electrostatic tubes) and hence if the deflection distance is to be proportional to the. (a) (b) Figure deflecting current the screen ought to lie wholly on the surface of an imagi- nary sphere with centre to centre of the coil assembly. Such a curved screen would be unsatisfactory, and practical screens are flatter than this, and in consequence the length of the beam increases with deflection angle, to produce greater sensitivity at the screen periphery, giving the grid of Figure The effect may be allowed for by designing the deflector coils so that the fields are not uniform {Figure ) but are stronger near the tube axis {Figure ). Deflection defocusing—This is a loss of sharpness of the spot as it is deflected away from the tube axis. It is attributable partly to the change in beam length due to the flat screen and partly to poor deflector coil design. The fringes of the deflecting field contain components which act along the axis of the tube to modify the focusing conditions {Figure ). The remedy is to have deflector coils which are long alo
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