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
Roly,
That's a nice little integrated amp there I would recommend keeping it, and sounds like you have a bad tube or tubes, at least that's most likely. When did your father in law last use it, or re-tube the unit? If you can't get that info or can't remember and you don't have access to a tube tester I would simply re-tube the whole unit. Luckily the tubes it uses, 12ax7, 12au7, 6sn7, and EL34 are all easy to find plentiful and can be found relatively cheaply. For power tubes Genalex Gold Lion KT-77's are a great choice, a drop in replacement for an EL34 its anything but a bright sounding tube. I haven't had any gear that uses 12ax7's or 12au7's so I won't make a recommendation there. For a solid basic 6sn7 something like Electro-Harmonix, or Tung-Sol reproductions should work fine. Good luck and if the problem persists that's a very easy unit to get work done on if you're in the USA.
Just swap the left and right channel tubes. If the trouble moves to the right channel then you will know it is a bad power tube. New EL34 tubes are only about 15 bucks each. I have used JJ EL34L power amp tubes and found them very nice. If you want to retube that amp, take a look at the Tube Depot site . BTW,I think the preamp tubes are the more important choice when choosing tubes. Keep that Amp!
It's a keeper.  You might need to re-tube.
I don't disagree that it's a nice integrated, however the SL6 is the wrong speaker to use with it. The SL6 is a power hungry, inefficient speaker that needs high current SS.
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.
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
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!
Sorry that should read if it persists in that one channel after flipping power tubes. Perhaps an issue with the bias circuit even?
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. 

Roly ,

It sounds like your left channel fuse protection has blown.

The fuse protector are located on each side of the amp between the far left and far right EL34 and the 6SN7 tubes. You will see there are "fuse out" indicators next to the fuse protection. If it is lit red then you have a blown fuse. You will need a Buss Fuse  BBS-3/4

If the fuse out light is red , power down the amp and just unscrew the black knob and the fuse will come out with the knob. This will also mean the one of your EL34 tubes have gone bad , so you will need to replace both left channel tubes , or you will keep blowing fuses.


So switching out the tubes didn't change the red light which stayed on in the V7 position, regardless of the tube placement. There are not other red lights or "fuse out" indicator lights on. I think I read something on another forum about a "plate fuse", but I can't be sure that was what was mentioned and I can't find the thread again. 
I will give a call to CJ tomorrow. I'm sure it will cost a fortune just to ship that beast. I see some upgrades on their page, anything you recommend if I send it in. 
As far as the SL6's, I think I will list them on here or on Ebay. I have enough speakers and if I keep the amp I will want to take that money and use it on a speaker set that matches the amp better, or to help offset any repair costs. Thanks again for all your advice. 
R
OH damn. They are at the CES show all week. :(  Have to wait until next Monday to get any answers. 
Hang in there R it's gonna all be worth it when you get that amp fixed up and singing.
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?
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. 
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.


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!
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. 




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."
However re-reading it, it's rather confusingly written as there seems to indeed be an active preamp stage incorporated into the CAV50.
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."
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.
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?
Jazz no mistrust was implied or intended dude I promise! And yes Roly any updates?
It has been a crazy holiday season for us. Finally just decided to stop trying to research all of the other tubes as well and just ordered some  JJ E34L's. I was up late last night trying to find some 12au7 and 12ax7, but started getting pricey since I don't know if the amp will need a major overhaul yet and I read that if I send in the amp for upgrades, often times they replace your tubes for you. So, waiting to buy other tubes but the EL34's should be here shortly and I'll see what they do. I am not hopeful it will fix the problem and not looking forward to shipping that beast to C&J.  I noticed some fuses (auto looking, blade-type) under the hood and behind the EL34's, so maybe I'll take a look at those today and make sure they aren't blown. 
If I keep the amp, which I probably will, I need to start looking for a great pair of speakers for them. I know Klipsch are super efficient, but typically too bright for me. I have seen several reviews and blogs about good speakers for them, so I'll probably start that search as soon as I test the EL 34's. $$$$$ It's always about the cash. Boo for not being rich. haha.
 You all have been very helpful. I'll keep you updated.
The tubes arrived, I installed them, let them warm for an hour, biased, then turned on some music. And.....the problem may be fixed. So, interesting thing when taking out the old tubes. All of the tubes had no markings on them but one, which read EL34G. That tube was in the paired channel where I was having the problem, though in a different socket. I only change the "bad socket" with another tube from the other channel, but never changed out that EL34G tube. It seems strange that a neighbor tube, in the same channel, could have been causing the bias light to light up and stay on its sibling tube, but that seems to be the case. So... now I have to find some amazing speakers to try out. Any suggestions for something that isn't super bright, has a high sensitivity and doesn't cost over, say $800? I know that isn't a huge budget. Thanks again for all your help. I have the old RBH speakers hooked up now and the sound pretty good. I have a call into RBH and have sent them pics so they can give me the model number and specs. They are old. No markings. I'll keep you posted.

Found out the info on the RBH’s built in 1993. 2 pairs, but I am listening to the larger model, the 812. The smaller speakers that match it are the 63’s. Here are the specs:
Specifications for 812: System Type: Acoustic Suspension 2-Way Woofer: 8" Long Throw Polypropylene Tweeter: 1" Liquid Cooled Polydome Tweeter Protection: Poly Switch Controls: Constant Impedance Tweeter Output Crossover (’ Frequency: 3COOHz. Attenuation Rate: 24 db/Octave & 12 db/Octave Asymmetrical Recommended Amp: 20 to 150 Watts (unclipped) System Impedance: 8ohms Frequency Range: 45 to 22,COO Hz Efficiency (SPL): 89db Cabinet Finish: Real Walnut, Oak and Black Oak Veneers ~aker nnection: 4-Way Gold Plated Binding Posts Cabinet Dimensions: 19" H X 12" w X 10.5’’ D Weight: 33lbs. each
and the 63’s: System Type: Acoustic Suspension 2-Way Woofer: 6" Long Throw Polypropylene Tweeter: 1" Liquid Cooled Polydome Crossover Frequencies: 3000Hz. Attenuation Rate: 12 db/Octave & 6 db/Octave Recommended Amp: 5 to 80 Watts (unclipped) System mpedance: 8ohms Protection: Poly Switch Protection Circuit Frequency Range: 60 to 22,000 Hz Efficiency (SPL): 89db Cabinet Finish: Real Oak and Black Oak Veneers ~aker nnection: 4-Way Gold Plated Binding Posts Cabinet Dimensions: 12" H X 8" w X 7" D Weight: 10 lbs. each ShipQing Weight: 25 lbs. / Pair

I know it is hard to tell much from stats, but would a more efficient speaker be better suited, or is all I am missing out on is the ability to go loud? Right now I can the volume to about 45% before it starts to distort a bit. I wouldn’t mind a bit more volume. Wish I had some Klipsch laying around just to test them.
Reading some reviews, here are some of the speakers tested with the system that people have enjoyed.  It is an old amp and all of the speakes look 1985-2000 range. Maybe this will help keep the cost down, but I doubt it.  Royal Reference 3A,  KEF 104/2,  Rogers LS3/5A speakers,  Totem Model 1 Signature,  Thiel 2 2's,  QUAD ESL 57's,  B&W N805s,  ProAc 2000 Signature speakers,  ProAc 2s,  ProAc response 1SC's,  B&W DM610
Anything new anyone would recommend? 
On another note, I am getting a mid-grade record player fixed and the CJ doesn't have any phono plugs/ground. Is there an affordable solution? 
I would also see if you can swing a pair of used KEF LS50 monitors that have a pretty good low end for monitors (is Stereophile Recommended Component Class A rated in a category that has many $5K+ speaker listed).  Can get for as low as $999 used (currently $1200 + $45 S/H with free $279 stands), new for $1500.  Try to get as much as you can the first go round to obtain highest performing products to delay future upgrades.  If full range is your desired path, their are the Monitor Audio Silver 8s (new $2000 (free shipping, no tax) or used $1400 with $200+ S/H) that are Full-Range Class B recommended.  If you live near Dayton, OH, can get the used version via local pickup to avoid S/H. 
So I am getting my record player back today. Should sound great. I am in need of a pre amp for it and wondering if I should go with a Tube Phono preamp and how that might interact with my CJ. Looks like they start around $180, whereas some of the SS ones go for $50. I would really like to keep it around $200, but willing to go more if the opinions are that it will make a  big difference. 
Also, BradwBradley, I see the sensitivity of the Kef LS50 is 85. Is that going to work well with my amp that doesn't put out a ton of power?