Help, strange glowing in KT88

taotao · 10th July 2009, 09:41 PM

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

tomchr · 10th July 2009, 10:47 PM

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

Ty_Bower · 10th July 2009, 10:52 PM

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.

6h5c · 10th July 2009, 10:56 PM

Looks like the grid is glowing, that's not good...

Ray

taotao · 10th July 2009, 11:25 PM

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

ray_moth · 11th July 2009, 02:13 AM

What happens if you swap the tubes arouind?

taotao · 11th July 2009, 02:03 PM

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

audioot · 11th July 2009, 03:02 PM

i think something is wrong with the cathode/filament on the upper side
is the valve working correctly?
audioot

taotao · 11th July 2009, 03:47 PM

Hey Audioot,

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

Bye
Olaf

audioot · 11th July 2009, 04:47 PM

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

10th July 2009, 09:41 PM	#1
taotao diyAudio Member Join Date: Oct 2004 Location: Cologne	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

10th July 2009, 10:56 PM	#4
6h5c One Seriously Addicted to Audio and Electronics diyAudio Member Join Date: Apr 2004 Location: Heerhugowaard	Looks like the grid is glowing, that's not good... Ray __________________ Gonna buy my little girl a pink soldering-iron The new DOS-CFP board is out!

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
7591 is glowing RED	dognut	Tubes / Valves	2	1st March 2009 06:16 PM
EL84s glowing red	twalker	Tubes / Valves	7	7th December 2006 02:50 AM
Vox tubes glowing red hot	Franconio	Tubes / Valves	10	4th April 2006 01:13 PM
7199 glowing purple?	GLF	Tubes / Valves	10	17th February 2003 11:08 PM
Blue glowing tube	Gabster	Tubes / Valves	24	27th September 2002 04:08 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read

10th July 2009, 10:47 PM	#2
tomchr diyAudio Member Join Date: Feb 2009 Location: Greater Seattle Area	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

10th July 2009, 11:25 PM	#5
taotao diyAudio Member Join Date: Oct 2004 Location: Cologne	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

11th July 2009, 02:13 AM	#6
ray_moth diyAudio Moderator Emeritus Join Date: Jan 2004 Location: Jakarta	What happens if you swap the tubes arouind?

11th July 2009, 02:03 PM	#7
taotao diyAudio Member Join Date: Oct 2004 Location: Cologne	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

11th July 2009, 03:02 PM	#8
audioot diyAudio Member Join Date: Jun 2008	i think something is wrong with the cathode/filament on the upper side is the valve working correctly? audioot

11th July 2009, 03:47 PM	#9
taotao diyAudio Member Join Date: Oct 2004 Location: Cologne	Hey Audioot, yes, tube is working correctly. It doesn't distort (audible) more than the other channel. Bye Olaf

11th July 2009, 04:47 PM	#10
audioot diyAudio Member Join Date: Jun 2008	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

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)