crt question
 

A long time ago I had a ctc5 that I got from Fair radio in Lima, Oh. I used a crt tester and the pic tube tested very good. Got the set home and replaced caps and at first had no raster. I thought maybe the crt had gone to air or shorted so I retested it.

The inside of the neck was vibrant blue when I tested but yet no shorts and still good emissions. Ok so now its gassy.

Out of curiosity I retried the tv and once I turned the brightness up I had a raster with plenty of brightness to it. I went around the back of the set and checked but no gassy blue anymore.

Everytime I put the crt tester on it ..same thing blue glow but not when running the tv.........Why is that?

The crt was a 21axp22

Then either what you were seeing was not a gassy tube but a bad CRT tester (they usually glow purple when gassy), or something was wrong with the set the first time you tried it and you fixed the problem when you reseated the connector on the neck of the tube. I had something like this on my CTC-7 not long ago, turns out not installing the focus rectifier results in no picture. So maybe your focus pin was just dirty and you knocked the gunk loose? <shrugs> These sets have a mind of their own anyhow, all of mine operate differently every time it turn them on. Just like old cars, every day a different knock or creak.

I was still intimidated by a color set so I ended up giving it to a member of this forum and sometimes I wish I still had it.
It was kinda rough and realistically needed a lot more work than I was qualified to do then. thanks for the answer as that has been bugging me.

My B&K makes a slight blue glow(not purple) on each gun when tested but my sencore does not do that when I know the CRT is good. When gassy, pretty much the whole neck glows purple.

I had a CTC-31 with an intermittent problem with the video output tube (as I recall). When it went out (for a few seconds) it would kill the raster and the neck of the crt would glow purple. I'm not smart enough to tell you why!

If the cathode current goes sky high, it could glow blue, but doubtful in a CRT, IMHO. I think you have a tube that's slightly airy, but still enough vacuum not to arc. I hope I'm wrong on that, of course ;-) .

Charles

I've got a rebuilt in 1981 21FBP that just before the HV comes up, the neck has a faint blue glow that disappears as the HV rises. It's done it since 1981, and the old CTC-10C is still going and going.

Light blue faint glow is just electron flow. You see this more often in audio tubes. Not abnormal.

agreed