CRT Question - Old Calculator

THat's what I should have asekd at the beginning... With 6 pin conenctions (+ the HV connecotr of course), this is not going to be an electrostatically-delfelcted CRT. Well, i suppose it jsut about _might_ be if only one deflection plate of each set was brought out to a pin, but that is so uncommon I think we can ignore this Everything seems to point ot it being an electromagnetically deflected CRT with electrostatic focussing. OK, 6 connecitons is quite a nroaml number. Two are the heater. Another is the cathode, whic his separate from the ehater, just warmed by it. Directrly-heated CRTs, where electrons are emitted from the hot filament do exist, but again are very uncommon. What is slightly more common is to internally conenct the cathode to one end of the heater, thus saving a pin. But that's not all that common either. That leaves 3 conenctions. We now have the rpboelm that the terminology is different on eitehr side of the Pond. In both cases, there is likely to be ana elctrode in front of the cathode, and -ve wrt to it. This is the cotnrol grid (simialr in concept to the grid of a triode valve, but in the CRT it's a metal cylinder, not a helix of wire), and is used for brightness cotnrol normally. There are now 2 more 'logical' electrodes. You call them all 'grids', reserving the term anode for the final accelerator, the coating on the CRT flare. We call them anodes, the only grid is the cotnrol grid. Anyway, typically there are 3 anodes, but A1 and A3 are linoed internally. this is the 'first anode', which effectively accelerates the electronds away from the cathode and sends them down the tube. The otehr anode, between them, known to me as 'a2' forms carefully controleld electric filed with the other 2 anodes, these focus the electorn beam. So of the 6 conencitosn we have 2 heater cathode control grid (brightness) first anode (accelerator, may nhbe used ot set overall brightness -the 'screen' cotnrol, etc) second anode (focus) As for modualtion -- that is turnign he beam on and off so as to eb able to drwa individual characters), this will typpically invovle varying the votlage tbeween canthode and control gird. Which can be done by varying e voltage of either of them. Veryign the cathode votlage is more common, but again it could be either. -tony