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Originally Posted by AlanInSitges
Speaking of which, and following on with the general theme of deflection and yokes, and not intending to hijack this excellent discussion, I wonder if someone can tell me if all of these huge pulses and inductors, etc., are strictly necessary. I mean, if one were to start over from scratch, in a vacuum, and set out to build a circuit whose requirements are to move an electron beam from A to B over a precise period of time, and given that we are already in possession of a waveform that exactly graphs that movement, would it be possible or feasible to simply drive a yoke winding from a simple power amplifier circuit? Both V and H?
I don't know how much juice is really needed to deflect that beam five inches on a 34CM CRT, but I do remember as a kid back in the 80s building a lissajous project from Radio-Electronics out of a 19" tube B&W set and a second yoke, and powering it from a 6L6 amplifier, and that it could very nearly move the beam off the screen. I've often wondered why, if that's the case, they didn't just put an STK chip or similar in these sets along with a SMPS for the HV.
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The output stage of both vertical and horizontal deflection circuits is a power amplifier. However, the horizontal deflection output stage has to deal with the high voltage created by the shock excitation caused by the rapid change in current flowing through the yoke during horizontal retrace or flyback time. In fact, this is one reason why the horizontal yoke inductance is lower than the vertical yoke inductance. Inductive impedance is higher, the faster the current is changed. The vertical deflection current's most rapid change is during vertical retrace, which is still significantly slower than horizontal retrace.