2. amps-preamps
  3. 119241-73122

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

Showing 3 responses by jazzonthehudson

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?
jazzonthehudson's avatar
jazzonthehudson
277 posts
 
I have had most CJ tube gear, including the PV10 and MV50 and I am pretty sure the CAV50 is based on the PV10/MV55 circuitry (I talked to the tech dept before buying the CAV50 as I liked the MV50 and had it for nearly a decade). In fact, the power stage of the CAV50 (12AX7 line stage for the gain, 6SN7 dual-triode driver and EL34 in push/pull for the power) is IMO (almost) identical to the MV50. 

The line stage of the PV10 (w/o phono stage) was based on a single 12AU7 (one half for each channel) which can be easily upgraded to a nice ECC82, IOW, that tube has a lot of influence on the overall sound. I recommend the Siemens E88CC Germany if you like great vocals, other reasonably priced are Philips E88CC Holland, Philips/Mullard E88CC UK and Amperex 6922 USA (orange label). Then you could upgrade the  12AX7 / ECC83 / 7025. 

As for output tubes,  JJ E34L has indeed great value/money. 

At the end of the day, the circuitry is based on the PV10 which is a good but not very resolving model like the PV12 at that time so one should not go crazy with tube rolling.

Jond, you are probably confusing it with the CA200, aka little brother of the venerable Premier 350,  solid state control amp that has indeed a passive preamp. 




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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