Quote:
Originally Posted by old_coot88
A 'spot killer' circuit would work by making the CRT control grid (pin 2) more negative relative to the cathode (pin 11), thus turning off emission. Same result by making the cathode more positive than the grid (as Notimetolooz mentioned in a previous post).
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Caution! A spot killer that works by biasing OFF the CRT has to hold the negative bias until the cathode cools or the high voltage decays, whichever comes first. Read my post about the burn problem on Motorola's first small transistor sets.
Many color sets killed the spot by turning the beam ON fully while the raster had not yet collapsed completely. You would get a short bright flash of a small raster, discharging the high voltage through the CRT before the raster had shrunk to a dot.