Purple color in CRT

[ketron281989]

After testing the CRT for that GE 802, 10FP4, I noticed that I could see a very faint color of purple in the back of the neck. Could someone tell me what that means? Everything from the tester checked out. The test results on the B+K 467: Good filament, good life, good emissions, and good tracking.

Thanks for the answers

Jon

[kx250rider]

That means that air has leaked in, so beware that the tube may arc when it sees high voltage. I would recommend not planning on using that tube, but on the other hand, it may have such a small leak, that it has taken 50+ years to leak to this point, and if it's going to take another 25 years before it leaks enough to arc, then obviously you're fine using it. If it's been in a damp environment, then likely the wires from the base have corroded into the glass, and have allowed a leak.

Charles

[Eric H]

Charles, this question has been gone over pretty thoroughly over at A.R.F.
http://www.antiqueradios.com/forums/...p?f=3&t=182773

The main consensus is if it checks good then it's good, the glow on the glass in normal, down inside the elements is Gassy and bad.
I've never seen a tube with purple inside the elements check good.

Some folks even think a purple glow on the surface of the glass indicates a very hard vacuum.

Jon, I'm not sure if your afraid it won't work or just looking for the Scientific answer to why it glows.

I'm quite confident it will function in your set, the Scientific answer will have to come from someone else I'm afraid.

Dammit Jim, I'm a Mechanic not a Scientist!

[ketron281989]

Jon, I'm not sure if your afraid it won't work or just looking for the Scientific answer to why it glows.



Thanks Eric your always a big help

I just wanted to know if the tube would still be good at performing, we will see when I am able to do a recap, but the fear factor that it was bad is cleared up thanks to you and the other forum members.

[Eric H]

I don't know right off hand if any forum members are near Cincinnati or not but it would be cool if you could find someone close by with a working set you could try it in.

[holmesuser01]

I've got a 21" roundie color. Just before the high voltage comes up, the neck of the CRT lights up a dull dim blue in a 2-3 inch wide area. Then, as the HV rises, and the CRT begins to charge up, it goes away, and the image comes up on the screen, as good as ever.

Bruce

[stusnyder]

[QUOTE=ketron281989;302284

I just wanted to know if the tube would still be good at performing, we will see when I am able to do a recap, but the fear factor that it was bad is cleared up thanks to you and the other forum members.[/QUOTE]

Have fun with that recap, especially the ones under the tuner. The lytics in the center of the chassis, you almost have to restuff the cans, no room to mount them underneath, too crammed in the first place.

[kvflyer]

Originally Posted by holmesuser01

...Just before the high voltage comes up, the neck of the CRT lights up a dull dim blue in a 2-3 inch wide area. Then, as the HV rises, and the CRT begins to charge up, it goes away, and the image comes up on the screen, as good as ever.

Bruce

I have noticed that most of my 7591 output tubes have quite a blue glow when they first start up. But after the B+ gets up to snuff and the tube starts to warm up, the blue is much less visible. So, sounds as though it may be normal.

[miniman82]

You guys are describing 2 different phenomena here. 'Blue glow' on the glass of good tubes of any type are actually stray electrons striking the glass, which gives the blue light we see. The purple glow is gas ionization between gun elements, they look completely different.

[holmesuser01]

I do hope that theres no purple glow between the gun elements.

[bgadow]

I always think back to a CTC-31 I worked on that had an intermittent with the video output tube (at least I think that's what it was). When it "snapped out" the raster would go away and the neck of the crt would glow a brilliant pinkish purple. I'm guessing it was losing an important voltage (wish I was smarter in that respect) causing those electrons to go in the wrong direction, or some such. So, there are possible reasons for it to still be okay, but I would prepare for the worst.

[ctc17]

Heres a video of a gassy CRT I came across. It does this when checking cutoff. http://youtu.be/iUW9Pf8UmJ4

[ketron281989]

Thank you ctc17 for the video, the 10FP4 tube with the purlpe was not as bad as that one. There was a very faint purple glow, you have to really concentrate to even see it, I have not come across it in the other tubes I have tested, could be because the HV is not hooked up. the faint glow is not in between the plates ether, that would be bad.

[mbates14]

Well, i have a zenith PV800 front CRT projector, and the red tube glows both red and purple all across the neck of the tube as soon as HV hits the electrodes in the gun, and the main anode. Also you can see faint electrons/ions "raster like lines/image" striking the face of the red tube when the HV comes up before the filaments heat up.

But funny thing is, the red tube still projects, and a good picture at that. BTW I am in the cincy area.