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Bias adjustment for the CARY SLI-80 Integrated Amp

To my fellow tube lovers: I have been here before, and I am back because I need help in solving an issue I have been having with my Cary SLI-80 Integrated Amp.
Very Simple: I cannot adjust the bias reading on the LEFT channel. After warm-up [about 10-15 minutes] I can set/reset the bias reading to 75-80 ma. Wait... there is more .... After about 30 minutes, with or without music, with the meter connected, one sees all of a sudden the needle jumping all over the place; talk about erratic readings: as low as 30 ma and then as high as 150 ma. When I try to adjust down the potentiometer, it gets to a point counterclockwise, where I can no longer adjust it, and it still reads a very erratic reading. If I adjust clockwise, the mamps start to go up even higher.
Either the outer-most power tube on the left gets RED HOT, or the power fuse blows. If I reverse the tubes [right to left and so on, one would think that the issue would be reversed, but it is NOT. Same erratic reading on the outer-most LEFT SIDE. SOMETHING IS WRONG IN THE WIRING INSIDE THE AMP. The problem is that the amp has been doing this now for quite some time and it has been sent back to Cary where they charge and tell me that nothing is wrong.

Where do I need help? Does one of you kind folk have a SCHEMATIC of the SLI-80 that I can get from you to see if I can track where the damage is? Or perhaps you’ve had a similar experience and knows where trhe problem lies. I really need help on this. Best to all and stay well during these trying times. Richard
128x128richfrank
oldhvymec
5,101 posts
 
First thing, swap to a DMM, digital multi meter. No room for error.

7-45 dollars.. Borrow one, use a different one..

Make sure your connection male and female are good and clean.

Especially on the amp that is messing up.. (Bias 1/4" female on the amp..)

Look inside. is it full of dust?

This stuff cost nothing if you borrow a meter.. Analog meters are BAD. They ALL need replacing, or at least calibration sooner or later..

THEN

Back the bias adj all the way OFF until it stops CCW on the amp that is messing up.. Flip on the Power wait and see if it blows a fuse. WAIT..

Then flip the standby switch.. WAIT... does it still blow a fuse before you start to bias?

I just went through TWO Carys one V12, one pair of 6 Pacs. Within 3 months they both lost the filter caps..

BOTH. Getting hot, and they both started leaking oil.. Though I had a ol Harley, or something.. ordered them up 165.00 and shipping and la te da. 225.00 for 4. Twice. Sure cooled the ops down, and LOL of course the oil leak.. Quit blowing fuses too..

Regards
oldhvymec
5,101 posts
 
If it doesn’t blow the fuse, and you haven’t biased. That’s one thing, you bias and it won’t hold the bias that different. Kinda sounds like the little resistor, for that valve is heating up and going out of spec. A signal valve can cause problems too.. don't think they can't..

I haven’t seen inside your amp.. but they aren’t that complicated...Carys.. pretty simple, but kinda messy for sure.. Actually really messy, inside.. :-)

Regards..
richfrank's avatar
richfrank OP
34 posts
 
To Jond: I don't live in the US, and the cost of shipping a 50 LB carton is very expensive. Second; I have sent it back to Cary around May 2020 and they claim they fixed it, and reset the bias,  and the bias issue was "all my fault". It worked for a couple of months.    What can I say .....

To oldhvymec: I believe you missed several points brought up by me:
1- The SLI-80 is an integrated amp with both Left and Right channels. 
2- The Digital Multimetr is not an issue because I can read BOTH sides independently, and when plugged into the right side, the meter is steady right at 75 ma (and the potentiometer reacts to my turning it CW or CCW).
It is the left side that the meter swings erratically. Logic would dictate that if the DMM were damaged, I would see similar irregularities on both chanels; that is not the case.  Only the left side does NOT hold the correct bias!
3- The SLI-80 does not have a "standby" switch.

Your second commentary seems to be more accurate. It could be a resistor. That is why I am asking if someone can obtain a SCHEMATIC for an SLI-80 Amp.

Please help me out here!
Regards ....
richfrank's avatar
richfrank OP
34 posts
 
Hello oldhvymec:   I reversed all the tubes; that is the left side tubes went into the right side, and viceversa. If it would be a tube, and only a tube, one would assume that the bias readings would be reversed, and that is not the case. After switching tubes, the left channet bias was still swinging wildly from 20 ma up to around 150 ma.  Sounds like a fliter ? or resister? giving me issues. My problem? I don't know which is the culprit.
Regards,
oldhvymec
5,101 posts
 
Good, you’ve narrowed it down, I say small valve because all these things cost nothing to check. I never use an analog meter. It’s the first thing I do..Cheep tool issues are just that, issues.. Can deal with that it’s a separate deal anyways.. Gonna need it to fix it..anyways... No analog meters...

https://www.trioda.com/index.php/en/equipment/4179-cary-audio-sli-80-signature.

I didn’t look real hard, you can’t upload or refer to a factory schemo.. They will edit the post. The above shows the inside pretty good. You can draw your own schemo. I did both of my Carys.. Shoot they are burned in my head.

Have you done a visual inspection yet? Might be easy to see.

Second remove the bottom inspection cover turn it on and LOOK, no toughing.. You might see the problem. Be patient though..

NOW turn off the lights and look inside... I’ve seen a lot of stuff that way.. Low light and arcing. Bad solder joints, ect.

One hand in you pocket, ay.. no two handed handling anything, unless your ok with it.. they can bite, ..LOL

Again this is a pretty easy unit, look at it... I’ll give it a 4th grader rating, only because they are one messy design.. Just sloppy...sloppy wiring.

If your gonna work on it.. discharge the caps, ALL of them, even the little ones.. they can bite, and scare you. You can knock the amp off the bench... LOL, well maybe not...

Regards..
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