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Cary SLI-80 bias help

I purchased a used SLI-80 with upgraded Shuguang Treasure 6CA7 Z power tubes. I decided to check the bias, which Cary says should be 75-100 mA per Channel. Using my GDT-11 meter I put the dial on the A-- portion and selected 200m. When I get the reading it is saying 4.5, obviously far off from what Cary suggests. Am I doing this wrong or is it really that far off? I don't know what effect that would have, but the amp sounds OK as is. I'm worried about truly putting that number at 75-100 in fear my reading is not right. I used this same meter though (it's brand new) to bias my Jolida amp and it was fine. Is 4.5 really 45 in this case?
vortrex
9 responses Add your response
stratoholic
4 posts
 
 75mA is too high for EL34 tubes.  I confirmed this with Cary.  They should be biased at 50mA.
artmaltman
769 posts
 
Ok Wikipedia says it's in the el34 family. My Svetlana el34s biased just fine at 75. It requires a very fine touch as it overshoots or undershoots easily.
artmaltman
769 posts
 
Are you sure the amp accepts that tube? I've used 6550, kt88 and kt90 AND el34 in my sli80 but never heard of the 6ca7 being in that same family.
czbbcl's avatar
czbbcl
1,752 posts
 
IMO ....Yes ..But I am not an Electrical Engineer... I use Genelax Gold Lions and bias them to 75 mA.

Chuck
vortrex OP
273 posts
 
Ok, I put the stock KT-88 tubes in and checked the bias the same way, it is 75ma spot on. So, apparently the previous owner never used these Treasure tubes or never re-biased the unit for them. The question now is, should these Treasures get the same 75-100ma?
vortrex OP
273 posts
 
It is warmed up plenty and I am using the 200m setting in the amperage as I mentioned. Any other ideas?
pehare's avatar
pehare
835 posts
 
Make sure you have your multimeter set for mA & set the dial for the closest number greater than 75mA so the bias reading will be less than the dial setting - then see what figure you get. You're probably using the wrong setting or scale so to speak. As Chuck says warm it up at least 20 min. or suffer more aggravation. It's a great amp, enjoy.
czbbcl's avatar
czbbcl
1,752 posts
 
I use a Radio Shack meter to set the bias on my SLI-80. It has a mA scale and I set it to 75. Not knowing your meter and what scale you have it set on it is difficult to provide you with a difinite answer. If you are on the mA scale which it sounds like you are then 75 would be the correct setting. Sorry I couldn't be more help.

Make sure the amp is warmed up before testing for the bias current as it will tend to drift when cold.

Chuck
vortrex OP
273 posts
 
The left channel is testing 4.5 and the right channel is testing 10.8.
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