? for Tube Guys

jdhdiggs

I have a 12AU7 tube on the output of my CDP. Right now (and this has been going on for a while but getting worse) the gains are different bewteen right and left channels. Could this be just the tubes fault?

faster100

That tube i believe has 2 sections.. like an ax7 and the like.. one section for each channel and if both arent matched pretty close you may hear a difference.. it would have to be pretty off though.. if tested , it would be like 100 % on the top triode and say 50 or 60 % on the bottom just as a example and that would mean less drive or output on the lower numbered triode..

IMO change the tube out and see what happens.. I have several 12au7's however my tester **** and it would be a crap shoot if they were matched or not.. get a new one

jdhdiggs

Right, so if I had a tester and wanted to ensure balance, which numbers need to match?

faster100

both, or pretty close.. all tubes of course test different at what ever life span they have been used.. if you tested it, the tester book will have different settings for each triode for that tube model.. ie: 12au7 each triode will have a reading of 0 - 100 or some such.. matched close as possible.. ie: 100 / 100 or 80 /80 or 80 / 90 is close enough to sound pretty equal.. BUt if ya dont have a tester it doenst matter get a new tube

[Deleted User]

Hello,
You would be measuring the transconductance of each of the tube's sections. Usually the tube testor will give different settings of the testor's adjustments for each section.
Regards, Ken

organ

The sections must be way off to make that much of a difference. Do you get distortion on the channel with less gain?

We can't say it's the tube until you get a replacement to try out. It's best to play it on the safe side for now and not use the player until you get a replacement. If it's the tube that's going bad, the problem could worsen to the point that the tube gets a short and you end up with damaged components on the cdp.

Which U7 are you using? It's also best to buy your *7 tubes from a dealer that screens for microphonic and noise. The tubes in the *7 and 6DJ8 family have a nasty habit of being microphonic.

First, try a replacing it with a current production tube so you don't spend much $. When you're ready for some kick **** sound, get a Mullard 12AU7. I had a pair with the newer logo and miss them very much. They're making music in Derick's (dcarlson's) rig now. I just purchased a pair from upscaleaudio.com with the old logo. These are suppose to sound even better than new logo, and I can't wait for them to arrive. Upscale is very well respected and is a sponsor on audioasylum. They test, match and grade each tube. What you'll get for a few dollars more is a non-microphonic, no noise and balanced triode sections. Check them out. Excellent selections.

Keep us posted on the problem.

Good luck

Maurice

jdhdiggs

I''ll check it out. Right now I have line attenuaters on the rig to put it back into balance. I'm not 100% sure it is the tube so I'll hold off on the Mullards until I'm sure.

faster100

is it one 12au7? if so i have several and can send you one..

jdhdiggs

Yup, just one. In the future though I'll be trying them on the frontend of the knights to see if I can get the levels to match the adcoms without attenuaters.