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To update, I powered the filaments off of the crt tester at 8volts and ran the rest off the set, but the glow remained. I let it run for a few minutes, tapping the neck and playing with the filament voltages, to no avail. Also tried holding a magnet up to the neck, just for the heck of it. Nope. As a last effort I pulled off the socket. Of course, 2 of the wires had to break despite my being careful. One of the grid wires, which left enough of a nub, but naturally the focus wire broke and did so flush with the glass. I was able to get a temporary connection for testing-I thought perhaps one/both of the wires was already broken and that was the problem. No, still the same. So, I am condemning this tube. I hooked the old crt to the tester again and it really is used up. The needle barely moves after hours at 8volts. I tried rejuvanation, and the filaments were lighting up like 12volts but as soon as it goes back down so does the needle. So, 2 bad 21 inchers...which bodes poorly for that DuMont across the room. Its good 21CBP4 could end up in the Zenith real soon!
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Bryan
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