Quote:
Originally Posted by bgadow
I had a CTC-31 that would go bezerk, it would lose HV with a pronounced "thump", the neck of the crt would glow purple, ouch! Turned out to be a bad video amp tube. I don't know why, I just know that was it.
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The circuit was probably designed to be DC coupled from that bad tube to the CRT. This is designed to maintain a dark scene without the blacks going gray. Many B&W TVs did go gray with scenes like that because the CRT was AC coupled to the video amp tube. So the bad tube would mis-bias the CRT, and possibly cause that purple glow.