Re: Open filament on CRT


This reminds me of a similar situation I encountered when I was a graduate student. My thesis advisor was collaborating with an industrial lab in another state; he got me a Summer job there. I was to get an apparatus they had built operational and, then bring it back to the university for my actual dissertation work. This was no insignificant apparatus. It was a masterpiece of glass blowing, etc - much more complex and larger than a typical CRT.

Unfortunately, when I tried to fire it up, the filament circuit was found to be open. It hadn't survived bakeout. The filament-to-support connections had been hard soldered. One of them opened up during the bakeout. Opening it up for repair would have consumed the entire Summer, a prospect which I didn't relish. I surmised that the bakeout had produced some corrosion or a break in one of the hard solder joints. My proposed solution was to use a Tesla coil (one of those 50 kV hand held units used in Physics labs for finding vacuum leaks, starting arcs, etc.) to zap the filament circuit (grounding one end and hitting the other with a spark). Amazingly, it worked. Whatever was impeding current flow was blown away and/or a functioning connection was made. The apparatus became useful. I survived the trip back to the university and I used it there for over a year and served its intended purpose without further filament mishaps.

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