CRT Question - Old Calculator

I can think of 2 : Magnetic focussing. If you put a longtitudinal magnetic field on the CRT, the electrons that leave the gun not on the axis will follow helical paths (apporcimately) with the axis touching each turn of the helix (_NOT_ with the helix centred on the axis as at elast one physics book I had to suffer said!). If you adjust the magneitc field, you can end up with the electrons ending up on the axis at the screen, thus prodcuign a sharp spot. Trace rotation. For mcu hthe same rason, if you have a logititudial magneitc field after the nrmal lelectorstatic delfleciton plates, you cna rotate the trace on the screen. This is sometimes done in good 'scopes to get the trace to exactly line up with the graticule lines (particualrlly if those are on the CRT faceplate, so the CRT can't be rotated wrt them. Now, an electormagetically-focussed, electortatically deflected CRT is very uncommon. I don't think I've ever seen one. In fact by the 1960s, magnetic focussing was rare anyway, it was easier to put an extra electorde in the electron gun than arrange the focus coil or mpermanent magnets. But... As otehrs haveaid, the number owires going to theis yoke is a good clue. A deflection yoke will ahve 2 coils (obviously). THis implies 4 wires. Magnetic defleciton is good if you want a linear-ish scan at a constant frequency. You cna use the self-inductance of the coil as part of an LR time constant. It's less good if you want anything else. You need a driver stage which cna overcoem the back-emf of the coil. For 'random' vector motion, this can incolve quite high voltages if you want a reasonable scan rate. Alas I am not (as yet) psychic. I can only base my comments on the facts I am given :-). And said comemtns are much the same as others have said. With the unit in fornt of me I may well notice things that are signfiicant (as woudl other people here), but until I see them I don't know they're significant... An accelerating anodebetween thre defleciton plates and screen (in an electrostaitcally deflected CRT) is not unheard-of, it is gnerally called PDA (no, not what you are thinking -- Post Deflection Aceleration). But it's normally only used in 'scope CRTs, If it's a vector display, there can't really eb a flyback transformer, in that there is no scan anf flyback. There will be an HV power supply, and this may well use soemthign that looks liek a normal flyback transformer -- in fact it may be a taansformer that is used a a flyback transforme rin a raster monitor -- but it will have its own drive circuitry. My worry is mcuh the same as yours. With onyl the HV vconnected, if the HV supply is operational, the whole CRT, inclduign any outer coatings, will get up to this votlages. They wil lthen flash over to anythign they can This is unlikely to b dangerous for you, but it may well zap transistors all fof the machine. -tony