[Quiet Earth]

An amp's output impedance will affect bass output (so may be beyond tube rolling).

Consider doing one or some of the very simple, well-documented crossover mods to lower the output of the midrange squawker and tweeter relative to the woofer.  Generally speaking, this restores the speaker's bass balance.  The Klipsch forum is a great place for this.

I think this is where the root of the issue probably resides. You need to find the right amp that works well with your Cornwalls, or learn how to do some work to either the speaker or the amp to get the synergy you are looking for. Not an easy task, I realize.

I always wanted a pair of Klipsch speakers when I was a kid but I could not afford them. Do you guys who know about the older Klipsch speakers know if the Cornwalls were voiced with solid state amps of the day, tube, or both?  Just curious . . . .

[Ericus Rex]

1. It had a bias adjustment screw on the back, even though its auto-biasing. Well there is also a input jack, which I thought was a headphone input! TUrns out thats where you check the bias current! Can I use a simple voltmeter? He said he should be about 120mv, 30 X 4, I got that. But then he said use the 200mv scale?
Can I just turn it all the way counterclockwise and slowly turn it as I listen?

You can't set the bias by listening.  You can use a simple multitester but you'll have to rig it up with a 1/4" headphone jack.  What that amp probably came with originally was a simple voltmeter (one with a needle) and a short cable with a plug on the end.  You can make one of those for a few bucks if you want.

Another thing; you'll need to use a matched quad of tubes since there is only one bias-adjustment pot.

[fz1jmp]

I hope this thread is entertaining and not just for me! I'm having a blast btw.

So. with the slight knowledge that counter-clockwise is lower, I gently turned up the bias about 1/8 a turn and well honestly is it possible that it helped this much? I mean really? I swear I just did that and the amp seems like a totally different amp. It's alive now!! I'm listening to Garcia/Grisman 'So What' and I hear the fingering so clean and crisp its scary. Now, when I spoke to the person who sold it to me, he really tried to sell me a quad of JJ KT88's, but I spend so much on the amp, it was just too much, But he said that its that. He thought the same thing when he got the amp!!! Then changed it out. I thought he was the original owner btw.

So, could a slight bias shift make this much of a difference?
Should I try out KT-88's? I'm guessing the current quad may not be optimal. I can always sell the KT's if its a flop. I know its only opinion, but I value yours!
I put the dang thing on 'gone! I think I'm pulling it cause I actually really like it now!!!

[Quiet Earth]

Well, as long as you are having fun then that's all that really matters. 

When you said "He said he should be about 120mv, 30 X 4, I got that." earlier in the thread, I thought you meant that you got the bias set. If you are just turning the screw without monitoring the bias, I would learn how to bias the tubes properly or your fun might not last as long as you want it to.

Keep working at it . . .   

[fz1jmp]

Well, as long as you are having fun then that's all that really matters. 

When you said "He said he should be about 120mv, 30 X 4, I got that." earlier in the thread, I thought you meant that you got the bias set. If you are just turning the screw without monitoring the bias, I would learn how to bias the tubes properly or your fun might not last as long as you want it to.

Keep working at it . . .   

LOL, I do understand the damage of over biasing. My Jolida had to be biased, but I just needed a voltmeter, no special input tips. I'm actually trying to find a broken pair of headphones and will make my own.

I just kept turning the bias till the tubes were a brilliant orange! Just kidding, just a slight maybe 1/8 turn. But that truly made a difference. I get the feeling between that and the seller stating what a big deal his JJ's made, well maybe thats the culprit.

[AB]

So, could a slight bias shift make this much of a difference?

That 1/8 turn probably wasn't a slight adjustment.  I would get that Voltmeter built to check it correctly.

When I first read your original post I thought "bias" immediately but I don't know that amp and so didn't reply.

[fz1jmp]

I thought it was an auto-bias unit. Until Dave from Cary mentioned it, I would never have given it another thought. What is the tool? I'm assuming that I cant just splice a headphone wire onto a lead on my voltmeter, where would I put the negative? I've searched far and wide and have not found it.

[munosmario]

I'm way out of my league here !!!

I figured, let me call AES, well Cary and just ask them about this amp. I spoke to a very very knowledgable person, Dave. I gave him my serial num and he said, hummmm, that has a bunch of tweaks you did not see on later models. So, 3 things I have no idea what he was saying;
1. It had a bias adjustment screw on the back, even though its auto-biasing. Well there is also a input jack, which I thought was a headphone input! TUrns out thats where you check the bias current! Can I use a simple voltmeter? He said he should be about 120mv, 30 X 4, I got that. But then he said use the 200mv scale?
Can I just turn it all the way counterclockwise and slowly turn it as I listen?
2. The review says it used 6922's, not the 6550's? Huh? Can I replace the 6550's with 6922's?
3. What the heck is the difference between tetrode and pentode mode? And sound?

I hope I'm not reaching with these questions, I would love to hear what this amp can do, I don't think I am.

fz1jmp, if I understand you correctly, the"tweaks" were performed by CARY itself, not a DIY or mod hired out by previous owner, correct? If so, rather than buying  or playing with more tubes, I would suggest, send unit to Cary to be bench tested there. Talk to Dave first and ask for a RMA (an email authorization or "booking" of your unit for shipment). Last time I used service (for my also factory upgraded SLP98 pre), there was a $125 bench charge that usually covers all testing/labor, plus cost of needed replacement parts or upgrades they recommend and you accept--you pay shipping both ways. You have a top factory "tweaked" version of a true high-end amp and I encourage you in your desire of giving amp a second chance..well worth it!! Are you sure unit is wired for "Pentode" and not "Ultralinear"? Clas A, zero feedback, Triode (15W) and Ultralinear (25W) were the originally specified two output circuit choices (with user performing a simple internal wire connection change--unit was designed as a kit). Don't recall hearing about a "Pentode" option but, obviously, it appears there was one.

Aside of sonic differences (with fans on both sides), the Ultralinear connection is more popular than Pentode in classic designs because it offers a good tradeoff between output power and impedance (the late David Hafler  popularized it in the 60-70's). Changing an amplifier from Ultralinear to Triode mode is a common modification. Triode mode has lower output impedance, less sensitivity to loudspeaker loads, and less feedback (hence softer clipping) if the circuit is unchanged, but also lower power. See following link for deeper discussion of differences http://www.diytube.com/phpBB2/viewtopic.php?p=3773&sid=5bf1fa9751df838c62a0090fc3bb83bd. Incidentally when calling Cary ask for Mark first. Dave is the service manager and Mark is the senior technician with more hands on technical knowledge of all Cary units. Tell him about your predicament, the type of sound you are seeking for and ask for his words of wisdom...once he gives you his wisdom/thoughts on the situation (since you are not DIY inclined, I believe) he most likely will suggest sending unit in and switch you to Dave for RMA (if he does not book it himself).

Good luck,

Mario 

[SteveFord]

I can help with the bias if nothing else.

If the amp is on please  turn it off.
You'll need two test probes - the negative lead on the multimeter should go into the negative speaker terminal and the positive lead should go into a bias adjusting pot.
Contact the previous owner or the manufacturer to find out where the adjusting pot is (it'll be a small hole somewhere on the chassis) and get a plastic screwdriver to adjust the bias with.

You do NOT want to use a metal screwdriver.  If you can't get a plastic screwdriver, make one out of a plastic knife.

The bias gets adjusted with the preamp on, speakers connected, NO volume or source playing and with the amp on for 10 minutes or so to warm up the tubes.
You should watch the multimeter while the amp is warming up as it sounds like you adjusted the bias without a meter?
As Ericus said, if the tubes aren't matched it's not going to sound it's best.

[AB]

I'm assuming that I cant just splice a headphone wire onto a lead on my voltmeter, where would I put the negative?

I think you do just that with the positive on the tip.
BUT I COULD BE WRONG.
I would call Cary again and ask.

[Early B.]

Biasing instructions should be in the manual.

[fz1jmp]

I'm going to apologize in advance, I'm not quote sure why the pic is upside down.

The input jack next to the fuse is the bias port I was told. Can I just stick in the probe? And the other on the negative speaker terminal? Dave added up the quad and said 120. That I can figure out.

Now, the idea of sending it back for a bench check, I did not think of that! Yes, the tweaks were all performed by AES as they were prototyping the amp, thats what I was told in great detail by the seller. Who, again, I find no fault with at all. We struck up a nice 'audio' friendship, he is an older retiree who enjoys his audio!

I'm sorry if I confused you, but yes its wired for Ultralinear. What exactly does it mean sonically? I tried researching it all day and really have no additional idea. BTW, I took a sick day today and again, enjoyed audio in 1 form or another all day.

munosmario; you seem to think its truly worth it, I so dont want to throw good money after bad. I actually put it on 'gone for what I paid. But now I'm tempted to pull it. The aleph 2's are good, but they just don't have that sound I seem to be looking for. I actually bought the Cornwalls just for there efficiency and figured they would be a perfect complement to the AES.

Anyway, great readings!!!

PS - I wish I had the manual, Cary does not have one either.

[Wayner]

Bias is based on incoming voltage. If you do not read the voltage when you set the bias, or allow the amp to "settle in" for a few hours, it will not be set "exactly right". However, most amps have a pretty broad range of where the bias should be set (at a specific line voltage) and unless you are at the extremes of the pot, you are experiencing "other difficulties" that I can't explain.

Wayner

[fz1jmp]

Well I did find a good definition of Ultralinear vs Triode

"Triode mode means wiring a pentode or a "beam power" output tube to operate in the same manner as a triode. This is intrinsically more linear but less efficient (i.e., less output power) than exploiting the extra grids (screen and suppressor grids) in a pentode. Here's a relevant thread:

Ultralinear mode is a particular application of feedback from a tap on the output transformer back to the power pentode to flatten frequency response and reduce distortion (THD) at any given power level. I b'lieve it was invented by David "Dynaco" Hafler (certainly looks like it).

I actually think I may use that as my reason to send back to Cary. Maybe, it may just make sense to sell it and look for a true SET amp. I think I will call them tomorrow and see what the cost would be. The thing weighs a ton and if its going to cost $500, I can probably pickup a decent low watt SET for $1300. So many choices.

[Ericus Rex]

Just sticking your positive probe into the jack probably won't work.  Go to Radio Shack and get a 1/4" headphone jack, but make sure it's NOT stereo.  When you take it apart at home, you'll see a solder lug and a section of metal that has cable crimps on it.  The solder lug in the middle part is your positive and the crimp section is the negative.  You can just put the plug into the bias jack without the cap on it (internals of plug exposed) and touch your meter test probes to the proper lugs and get a reading.  (the better way would be to buy an extra set of leads at Radio Shack, cut off the probes, and just solder the positive and negative wires directly to the lugs).  Then follow Steve Ford's advise about biasing.  30mV per tube sounds a little low.  You could safely go between 30 and 40mV and be fine.  I would think if you turned the bias pot counterclockwise you have raised the bias.  I guess there's no guarantee the seller rebiased when he returned the 6550s to the amp.  They could have been severely underbiased.

[SteveFord]

Would alligator clips work on that?  Stick the negative into the jack and clip the positive to the positive speaker post/spade?
I don't know about this amp but with VTLs you can really get the bias way off.

[munosmario]

I'm going to apologize in advance, I'm not quote sure why the pic is upside down.

The input jack next to the fuse is the bias port I was told. Can I just stick in the probe? And the other on the negative speaker terminal? Dave added up the quad and said 120. That I can figure out.

Now, the idea of sending it back for a bench check, I did not think of that! Yes, the tweaks were all performed by AES as they were prototyping the amp, thats what I was told in great detail by the seller. Who, again, I find no fault with at all. We struck up a nice 'audio' friendship, he is an older retiree who enjoys his audio!

I'm sorry if I confused you, but yes its wired for Ultralinear. What exactly does it mean sonically? I tried researching it all day and really have no additional idea. BTW, I took a sick day today and again, enjoyed audio in 1 form or another all day.

munosmario; you seem to think its truly worth it, I so dont want to throw good money after bad. I actually put it on 'gone for what I paid. But now I'm tempted to pull it. The aleph 2's are good, but they just don't have that sound I seem to be looking for. I actually bought the Cornwalls just for there efficiency and figured they would be a perfect complement to the AES.

Anyway, great readings!!!

PS - I wish I had the manual, Cary does not have one either.

My advice would be to call Cary and talk to Mark.  He will be able to give you an idea of overall cost to make it sound at the same league--if not better--as the unit that gathered all the rave reviews. Re shipping you should already know...how much shipping did you pay when you bought it, $50-75? Assuming $75, that will be $150 both ways plus $125 bench charge, equals $275. If you paid, I believe, $850 we are at $1125. That leaves about $300 room for part replacement, if any, before getting to the equivalent of $1400 regular production Super Amp, a known hi-end commodity that gathered all the rave reviews (remember, for the sake of accurate math, if you manage to sell unit at cost, you will be getting that cost minus Agon new listing/commission charges).

All the best ,

Mario

[SET Man]

Hey!

   I remembered this AES stuffs from a decade ago. Cary used to have a DIY mail and Internet parts store if I remembered correctly.

   Sorry  to hear about your problem with this amp. Buying a used audio is not 100% hassle free, especially with tube stuff. I would have done more research on it before, like what tubes it come with, any mods and what are the original tube configuration, how old are those tubes and so on.

    Anyway, I don't think this amp should sound much thinner than the Pass. You've mentioned that it sounds "...almost distorted..." That doesn't sound right.
 
    OK, like other mentioned before, make sure the bias is correct. I see that the amp use a 1/4" phone plug. So, if you don't have one go to Radio Shack and pick one of this...

http://tinyurl.com/9qmkme8

    Take the sleeve out, plug it in and use your meter prob on the plug contacts, use gator clips would be easier if you have some. Set the bias and see how the amp sound.

   Another thing that I think is the problem is the 6BQ5/EL84 tubes. You mentioned that the original tube config is 6CG7. The 6CG7 is small signal dual triodes tube and the 6BQ5 of which is a power tube. Something is not right there. Did you mention this when you called Cary? Had the amp been moded to take 6BQ5? If not I would look for a pair of the 6CG7 and replace them.

   Anyway ,good luck. Don't give up yet. But you can just skip all the hassle and go straight to a good SET. Well as long as you have a speakers to go with... I would look for a nice used one to save money, a US, UK or Euro made one would be nice    

Take care,
Buddy 




     

[fz1jmp]

Well, I said no more thanks, but I have to say thank you to the links for parts and the great financial analysis. At this point I want to see what this amp can do, I do think it was not biased correctly and when I spoke to the seller, he did say he did not re-bias it for the 6550's he put back in.

I picked up the 1/4 plug and warmed up the amp, turned off the source and lowered the volume to 0. I have a craftsman 82139 multimeter and 1st put it on mA, but that did not seem right. Then I put it on VDC, and tried mv, got OL (over load). Worked to V, but then noticed the voltage was going lower as I turned the bias up. So, I took the plug out and tried music. No dice. Sweat, panic... Check the fuse Jack, check the fuse.... Uh Huh, thank god for fuses. It blew. May of been when my hand slipped and the positive slipped to the negative.... So, 1/2a 250v Radio Shack here I come.

So what would be the right setting on a multimeter/ The 6550's are not really bright, so I'm assuming they are low. On mA it was reading like 300, then I brought it down to 160, but I'm not sure thats the correct range.

So my saga continues. But I see light at the end in a sense, I'm beginning to hear decent sound.

[fz1jmp]

Let me add some more to my story and I hope at least your enjoying it. I found a 1/2A fast fuse in my Mc tuner. Then, I decided to call Cary. The person who I spoke with, not Dave like I said yesterday, Mark was a sheer pleasure to talk with. I was taking tubes out and sticking the multimeter leads in slots like I knew what I was doing! Turns out its a fixed bias amp, which surprised even him. When I verified, but black on ground and red in slot 5, that each socket was controlled by the 1 bias adjustment. The amp was definitely biased too low when I got it, hence the horrible sound. I finally biased it at 200ma, which he said should be 50ma per 6550. KT88's would be more like 240-250.
I think I may just listen to the music now, and pick up a quad of GL's. I saw a decent price of less then $200 from a decent vendor.
Thanks everyone for your help and comments, invaluable!!!