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May 29, 2016
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Rejuvenating the guns on a CRT affects focus. Is this something that's widely known and I have just missed the memo?

I picked up a B+K CRT analyzer years ago, because I had a few worn out tubes that looked dull. I've only ever heard people using a rejuvenator for this symptom, so that's what I've done myself. Results have been varying. Almost all tubes gain more color intensity, but some tubes go back to looking dull in 20-50 hours. I've never used it on anything that has OK color reproduction (like most tubes), because rejuvenating shortens the life of the tube by removing some of the coating off the cathode and there's only a finite amount of it.

Anyway, sometime back I got a Wells Gardner K7400 with a really blurry, out of focus image. I swapped the chassis on it, same problem. I tried playing around with the yoke (removing and reseating it) and pulled out the yoke ring set and tried to find the sweet spot somewhere on the neck where the pic would be sharp. Absolutely wasted effort. The grid in the geometry test screen was pure white (so convergence was OK), but all the lines were a good 3-4 mm thick (they should be 1mm with a good tube). Even though I was sure it would never look good, I connected the B+K to it. All three colors showed good on the dials and the focus light lit up, so the analyzer was saying the tube is fine. Whatever, nothing to lose on this tube, I still hit rejuvenate on it.

Surprise. The screen was pin sharp afterwards ?(

I rejuvenated a MS2934 last week. Colors were absolutely fine on it, but the image was soft. Result: it looks amazing now. Picked up a Toshiba PF sometime back from Yaton. Again, nice vibrant image, but you couldn't make out any of the small text on Outrun 2 because everything was just slightly out of focus. Again, amazing result. I'm telling you, the difference is huge.

I hate a smeary looking picture. If I'm shortening the life of a tube, so be it.

Someone with a lot of CRTs, a rejuvenator and a fuck it attitude, try it out. Pick out that monitor that you consider second tier, you know, the one that looks OK, but nowhere near as good as some of the others, and rejuvenate all three guns with the lowest setting. Report back.
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