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Old 10th July 2009, 09:41 PM   #1
taotao is offline taotao  Germany
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Default Help, strange glowing in KT88

Hi Forum,

in my DIY Ella amp, one powertube shows a strong bright light.
I tried to photograph, but pictures have gotten unsharp.
But anyway one can notice, where this bright spot is located.
It's only one from 4 tubes showing this light. Bias is for all tubes equal (conservatively 45mA).

Could it be the tube will go to fail in the nearer time?
And what's causing this spot?

FYI: this spot wasn't there, when tubes were new.
I only noticed two days ago, bias was quite on the high side (around 79 mA, don't know why. I adjusted it to the above mentioned value)

I appreciate your input.

Pictures:
http://i852.photobucket.com/albums/a...n/DSC01576.jpg
http://i852.photobucket.com/albums/a...n/DSC01577.jpg


Olaf
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Old 10th July 2009, 10:47 PM   #2
tomchr is offline tomchr  United States
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Try setting the camera to macro mode if it has one. It's usually indicated with a flower icon and will allow you to focus at close distances. - Or shoot in high resolution from further away and crop the image.

It looks like one heater is running hotter than the other. Could be a hot spot that has developed... But it's pretty tough to see on the pictures.

Tom
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Old 10th July 2009, 10:52 PM   #3
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Quote:
Originally posted by tomchr
Try setting the camera to macro mode if it has one. It's usually indicated with a flower icon and will allow you to focus at close distances.
Good photography tips. I'll also add that it makes it difficult (if not impossible) to focus on close up objects if you use the zoom (telephoto) feature of the camera. Keep it at the wide angle setting (1x) for best results.
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Old 10th July 2009, 10:56 PM   #4
6h5c is offline 6h5c  Netherlands
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Looks like the grid is glowing, that's not good...

Ray
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Old 10th July 2009, 11:25 PM   #5
taotao is offline taotao  Germany
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Oh, well, "not good" that also comes in my mind.
Tomorrow, I'll try to take better pics.

Thanks for first responses.

See ya
Olaf
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Old 11th July 2009, 02:13 AM   #6
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What happens if you swap the tubes arouind?
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Old 11th July 2009, 02:03 PM   #7
taotao is offline taotao  Germany
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Hi Members,

the glowing moves with the tube, when I put it in another socket.
So the tube is faulty.

Here are more tries with macro modus (not perfect, maybe OK for recognizing, what's the problem):

http://i852.photobucket.com/albums/a...n/DSC01590.jpg
http://i852.photobucket.com/albums/a...n/DSC01591.jpg
http://i852.photobucket.com/albums/a...n/DSC01592.jpg
http://i852.photobucket.com/albums/a...n/DSC01593.jpg
http://i852.photobucket.com/albums/a...n/DSC01595.jpg

Thank you


Olaf
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Old 11th July 2009, 03:02 PM   #8
audioot is offline audioot  Belgium
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i think something is wrong with the cathode/filament on the upper side
is the valve working correctly?
audioot
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Old 11th July 2009, 03:47 PM   #9
taotao is offline taotao  Germany
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Hey Audioot,

yes, tube is working correctly. It doesn't distort (audible) more than the other channel.


Bye
Olaf
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Old 11th July 2009, 04:47 PM   #10
audioot is offline audioot  Belgium
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probably the cathode sleeve is a bit shorter en you see the bare filament glowing
in that case you have nothing to worry about
greetz from belgium
audioot
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