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Audio research tube bias setting

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Posted on May 30, 2016 at 08:42:08
lefty707@hotmail.com
Audiophile

Posts: 10
Location: Amherst ny
Joined: February 21, 2015
 I have an Audio Research Classic 60 amplifier. Bought it with electro harmonix kt90 tubes. For some reason the four tubes on the left side will not come up to bias, if I raise the bias on the left side quartet, then the right side is over bias. Is it the tubes or something else? I don't know if the amp was designed for kt90 tubes.

Thanks!

 

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RE: Audio research tube bias setting, posted on May 30, 2016 at 08:56:59
Palustris
Audiophile

Posts: 2408
Location: Cape Cod
Joined: September 12, 2008
 You unit has some kind of servo circuit to maintain DC balance in the output tubes. There is a method of servo balance calibration outlined in your manual. I would definitely contact ARC before messing around with it.

 

RE: Audio research tube bias setting, posted on May 31, 2016 at 13:03:09
deafbykhorns
Audiophile

Posts: 1067
Location: Florida
Joined: October 17, 2003
 The servo balance circuit may need to be adjusted due to aging components. This circuit takes care of the V5-V8 tubes.
This normally does not need adjustment unless you have moved the pots previously or changed tube types. Make sure you use a plastic adjustment tool for this task.
The bias is just for V9-V12 tubes.
Tubes should be matched set for best performance.
Give me a ring if you need a hand

 

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