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In Reply to: RE: Cary SLI-80 tube bias posted by Jim McShane on March 03, 2016 at 10:53:11
I used to own a SLI80. When the Cary supplied current meter was connected it measured the bias current in both tubes of the measured channel. So, 80mA measured was the total for the output pair. No provision for balancing the two tubes. If I remember correctly, Cary recommended 70mA to 80mA total bias or 35mA - 40mA/tube. Fairly conservative for a class AB1 amp. Not crazy low like some of Bobby Carver's latest creations at 15mA/tube. :~D
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
Follow Ups:
I normally set the bias at 70mA, or 75mA with GL KT88 tubes. Someone told me to set the bias at 50 or 60 mA with vintage TungSol 6550 or GEC KT88 tubes, but TS 6550 proved better with bias set at 70mA/pair.
I remember the RFT EL-34s sounded good with bias set at 60mA/channel.
Not long ago I contacted Cary about bias for KT77 tubes and their recommendation was 50-60 ma. I believe my manual says bias for stock tubes, KT88 or 6550's, is 75-100 ma.
That is for more than one tube, yes?
"Little details" like that are critical. That's why people need to pay attention to the maker's bias recommendations. That's not to say you can't try different settings, but the "spec" is a very good place to start.
Yes Jim,
The Cary has a bias pot for each set of two tubes.
I try to keep the bias set at 75-85 ma on KT88, KT120, and 6550 tubes.
Haven't experimented with any higher or lower settings.
Edits: 03/04/16
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