Sometimes on a set with AKB, it will do the opposite, and you will see the guns come on with too much drive (because the emission is low until the cathodes warm up and also because the filter capacitors in the AKB circuit need to charge up), and then get turned down (although the fact that the cathodes are warming up at the same time keeps it from being too bright). I had a Zenith in which the three guns reached equilibrium with slightly different delays, so the gray scale had three noticeable adjustments occur, one after another.
Maybe this could also be a channel change / source change blanking of some kind that happens to operate when first turned on? Would be interesting to see what it does when switching between sources or changing RF channels.
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