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Conrad Johnson CAV 50

Just acquired this beauty from my father in law. I've never owned a tube amp, so not sure if I should sell it, or keep it and pay him. Anyway, a question for you tube heads. One of the EL34 tubes in slot V7 ( a tube which can have it's bias adjusted, which I assume means the power transmitted) has it's red light constantly on. I turned the bias all the way down and it still flickers. However, I noticed that my left speaker sounded blown/distorted. When I turned the bias up, the distortion decreased. The instructions say to turn the bias down/counter clockwise, until the red light goes out. But, if I do this, it sounds bad. So, my question is this. Is it simply a tube I need to replace to fix that problem, and if I change one tube, should I change them all. Next question is I searched for the EL34 tubes and of course there are a large variety of them. Any thoughts. To me the amp sounds little bright with the Celstion SL6's I am using, so any warmer tubes would be nice. Also, if I were to sell this setup, any idea on what I might ask on pricing? Thanks.
Roly
rolyasm
jond's avatar
jond
5,794 posts
 
tls49 you're right just looked at the specs for the SL6, that's probably also why the OP is perceiving the sound as bright.
rolyasm OP
14 posts
 
Thanks for the replies. I changed the power tubes (EL34) to the opposite sides and the problem persists. It might even be that the distortion can be eliminated by having the bias all the way up and having the red light solid constantly, but I am worried this may be bad for the amp. Any other suggestions? I tried another speaker, a cheap one that I assume is easier to push, and it doesn't change the problem, so I am guessing it is not related to the speaker being to difficult to push, but an amp problem. 
TLS49, from what I have read, you are totally correct about he SL6's. It is interesting that when he bought this setup years ago at a high end hi-fi shop, this setup is what they recommended. Part of the reason I was thinking of selling this combo is it just doesn't sound good, but now I realize it is probably just the speakers being mismatched with a low power amp. Thanks for confirming that. 
Jond: I don't think he has ever changed the tubes. Although he has probably only had the amp on maybe 100 hours over the last 10 years. So the tubes probably just all need to be changed, unless time doesn't affect them, and only usage. 
Thanks for your ideas. If you have any more about where to proceed with the bias light, or whether I should even worry about it, all is welcome. Thanks for your time.
R
jond's avatar
jond
5,794 posts
 
Roly you may also have another issue if it persists in both channels, perhaps a blown resistor or leaking capacitor, hopefully almarg or one of our more tech minded members will chime in with a better diagnosis. Or you can always simply call or email C-j on Monday. Either way good luck!
jond's avatar
jond
5,794 posts
 
Sorry that should read if it persists in that one channel after flipping power tubes. Perhaps an issue with the bias circuit even?
tls49's avatar
tls49
1,351 posts
 
I changed the power tubes (EL34) to the opposite sides and the problem persists.
Did the problem stay on V7 or did it move to the other side? If it stayed on V7, the amp may need to be looked at by a technician. If a tube cannot be biased properly, that should be corrected. Playing it long term will definitely not be good for the tube and if a defective part of the amp is causing the problem, that could affect other parts in the amp as well.

Even if the amp is working properly with new power tubes, it still won't be able to get maximum performance from the SL6. 

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