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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
6,056 posts
 
Hang in there R it's gonna all be worth it when you get that amp fixed up and singing.
jazzonthehudson's avatar
jazzonthehudson
277 posts
 
I am not a tube techie but judging from the symptoms described you may have a leaky coupling cap; usually 0.22mF 600V. If you call CJ, their engineer (Jeff) will probably ask you to ship it in for repair as you already did the swapping of the (EL34) tubes. Not sure where you live but if you were near NYC, I can recommend you some great tube repair shops as the CAV50 is pretty standard.

FWIW, I had the CAV50 for awhile in my library setup, if I remembered correctly it had the same or, at least similar, power stage design as the MV50. Not bad when you rolled the line stage tubes.

As for the SL6’s sound bright with the CAV50, did you try the speakers in another setup?
rolyasm OP
14 posts
 
Still waiting on a call from CJ. I went to a local shop ( UTAH) and they said CJ is a company that doesn't give out schematics so they can't work on it and I have to send it in. :(  The local owner recommended the Mullard EL34, and I have recommendations for the Genalex Gold Lion KT-77 and the JJ E34L. Is it really going to sound different with these different tubes, and if so, should I just roll the dice, or do any of you vets have experience with all three of these recommendations and can offer me some advice. Lastly, I think these tubes are all original and probably have never been replaced, although the amp has only been used less than 100 hours during that time. Do tubes degrade, and if so, should I just do a mass exchange of all the tubes? 
JAZZONTHEHUDSON: What do you mean by "rolling the line stage tubes"?
I did try the SL6's in a solid state setup, and they sounded fine. Not as good to me as the mid-to-hi-grade RBH I was comparing them to. But with a solid state and my record player, it was nice. Might keep them just for retro sake. 
solman989
44 posts
 
I've tried all 3 of those tubes and prefer the JJ E34L.  I find that it is the most balanced top to bottom - organic mids, not too bright, not too slow, and no lack of bass in my setup.  Plus they are cheap to replace.  There are proponents for each of those tubes, and ultimately you should hear them all to make up your own mind on what best matches your overall system. 

If the total time is 100 hours on the tubes, that is relatively low and I would just keep them.  I actually think tubes sound better once they have around that much time on them vs brand new.  However, replacement may be a good idea if you do not know the history of the tubes.

The line stage tubes Jazz is referring to are the smaller 12AX7 tubes.  If you feel the need to splurge on tubes, make it these ones and/or the phase inverter 6SN7 tubes.  These are small signal tubes and as such will have a greater effect on the overall sound, more so than the output tubes IMO.


jond's avatar
jond
6,056 posts
 
Roly the CAV-50 is an integrated so it's an amp and preamp combined in one chassis though it doesn't have an active preamp stage so it's really a passive preamp. So what I'm sure Jazz is referring to are the small signal tubes you have 1 12au7 and 2 12ax7's both types are very easy to find and plentiful. You also have 2 6SN7's that are probably input tubes of some sort for the amp stage. Rolling any of the tubes can potentially change the sound just like changing the power tubes will, so have fun and welcome to the world of tubes!
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