Tube wont bias...

JayH3 · 5th July 2008, 06:42 PM

Just finished rebuilding my diytube st70 circuit. In biasing the tubes I found that one of them would only get up to about 20mv. I inspected the circuit, thought I found a fault, and resoldered it. Put it all back together and was happy I was getting appropriate voltage there until I found the problem just moved to the tube next to it, so I swapped tubes and the problem followed the tube.
Is there anything else I should consider before I convict the tube? The tube is a JJ E34L that I purchased as a matched quartet and has about 5 hours on it. Everything biased good before the rebuild.

Sal Brisindi · 5th July 2008, 07:48 PM

If it followed the tube, then I would say the tube is bad. I read in another forum the quality of the JJ tubes especially the EL34's is not good.

Sal Brisindi

JayH3 · 5th July 2008, 08:26 PM

Quote:

Originally posted by Sal Brisindi
If it followed the tube, then I would say the tube is bad. I read in another forum the quality of the JJ tubes especially the EL34's is not good.

Sal Brisindi

Pretty much what I thought...

Did you hear the build qualitly was bad or everything about it. They seem to sound great.

Sal Brisindi · 6th July 2008, 01:03 AM

I never tried JJ tubes but from what I read in a few forums, I would not buy them at all. I friend of mine had a bunch of EL34's that like to give a light show (sparks) inside the envelope.

Sal

TubeHead Johnny · 6th July 2008, 04:41 AM

JJ's are excellent sounding tubes, but their QC isn't what it used to be. I just picked up a set of KT88s, and after about 20 hours, one became a drifter. TubeDepot sent me a replacement within 2 days, now every thing's great.

5th July 2008, 06:42 PM	#1
JayH3 diyAudio Member Join Date: Mar 2008	Tube wont bias... Just finished rebuilding my diytube st70 circuit. In biasing the tubes I found that one of them would only get up to about 20mv. I inspected the circuit, thought I found a fault, and resoldered it. Put it all back together and was happy I was getting appropriate voltage there until I found the problem just moved to the tube next to it, so I swapped tubes and the problem followed the tube. Is there anything else I should consider before I convict the tube? The tube is a JJ E34L that I purchased as a matched quartet and has about 5 hours on it. Everything biased good before the rebuild.

6th July 2008, 04:41 AM	#5
TubeHead Johnny diyAudio Member Join Date: Jan 2005 Location: The Electric City, Schenectady, NY.	JJ's are excellent sounding tubes, but their QC isn't what it used to be. I just picked up a set of KT88s, and after about 20 hours, one became a drifter. TubeDepot sent me a replacement within 2 days, now every thing's great. __________________ "No man really becomes a fool until he stops asking questions" - Charles Proteus Steinmetz

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5th July 2008, 07:48 PM	#2
Sal Brisindi diyAudio Member Join Date: Nov 2006	If it followed the tube, then I would say the tube is bad. I read in another forum the quality of the JJ tubes especially the EL34's is not good. Sal Brisindi

6th July 2008, 01:03 AM	#4
Sal Brisindi diyAudio Member Join Date: Nov 2006	I never tried JJ tubes but from what I read in a few forums, I would not buy them at all. I friend of mine had a bunch of EL34's that like to give a light show (sparks) inside the envelope. Sal

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