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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
5,903 posts
 
Jazz no confusion I read this on c-j's website regarding the CAV50:

"Because each element of an audio circuit introduces its own sonic colorations, a simple circuit should be expected to yield superior musical performance. At conrad-johnson, we have maintained a commitment to designing simple, straight forward circuits for audio components. The CAV50 elevates this design philosophy from the circuit level to the system level by eliminating the preamplifier altogether and incorporating the control functions on the amplifier chassis, hence the term "control amplifier". This approach completely eliminates the inherent colorations of the active circuitry embodied in a preamplifier stage, and of the cabling between preamp and amp. The result is a significant improvement in system performance and convenience, combined with a reduction in cost."
jond's avatar
jond
5,903 posts
 
However re-reading it, it's rather confusingly written as there seems to indeed be an active preamp stage incorporated into the CAV50.
rolyasm OP
14 posts
 
A rep from a tube store wrote me and here is what he had to say about a few tubes I was looking at.....
"The EL34 is a pentode. A pentode has a suppressor grid in addition to the control grid and screen grid. The power pentode was developed by Philips in the 1930s. RCA developed the beam tetrode which has a set of beam plates instead of the suppressor grid. At the time Philips held the patents on the power pentode anyone who wanted to build power pentodes had to pay Philips to obtain licensing to build them. RCA developed the beam tetrode so they could build tubes that functioned like a power pentode and not pay the licensing fee. The 6L6 was one of the first beam tetrode tubes. Compared to the EL34 pentode, the 6CA7 and KT77 beam tetrodes will have a little more bass response and sound warmer."
jond's avatar
jond
5,903 posts
 
I would agree with that pretty much though I prefer the KT77 to the 6CA7 in my system. I had JJ 6CA7's still have them around as backups. I did also just put in a new quad of Psvane Philips Holland Metal Base EL-34's and they are quite good a bit more top end and maybe a touch more transparent than the KT-77's another nice tube. A bit pricey at $330 but I managed to pick up a "new" used quad for $250.
jazzonthehudson's avatar
jazzonthehudson
277 posts
 
Jond, a little trust would not be misplaced. After all, I had the CAV50 and, as mentioned, owned most CJ tube gear.
"control amplifier" is how marketing people tried to differentiate it from an integrated amp. 

rolyasm, has your CAV50 been diagnosed yet?
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