2. amps-preamps
  3. 128348-7795

Qs about Bias

I posted it in my other thread about ARC Ref 110 but I guess nobody followed on the old topic since I Didn't see any replies.

After I put new KT120 in my ARC Ref 110 I adjusted the bias after a few hours and again after about 50hrs of play.
Few Questions:
1. when adjusting bias I understand the amp has to be warmed up but also disconnected from the speakers and the pre-amp....is that correct ?
2. The manual says to adjust the main tube to 65mV and only check the slave tube to ensure it is between 55 and 73mV...when I use my digital meter I get to 65mVDC but it jumps between 64.8 and 65.3....never seems to actually stop at exactly 65.0mVDC
3. In addition the slave tubes in the pair always displays negative voltage....and I made sure I use the probes correctly and don't reverse the polarity... so let say I adjust the Bias till I get 65.2 and then check the other tube and get - 60mvDC....so this is in the range but shows reversed current.

Hope to get some clarity on this process....THANK YOU!
ether

Showing 1 response by lostbears

lostbears's avatar
lostbears
538 posts
 

 You do not disconnect anything. You just have no music playing for a few minutes. I put my preamp in mute. The amp needs to be warm to bias the tubes. I normally bias my tubes after listening. The amp should be on for at least 15 minutes. You also need to check the bias often with new tubes. New tubes tend to drift. Tubes that are not burned in a bit before matching will can a lot. Then you have to move the tubes around to get a closer match.

 The tubes do not seem well matched. You need to used tubes that are well matched so you don't have a large variance between the pair of tubes. Every tube in my Ref 110 is at 64 ma. There is next to no variance at all. I get my tubes from Jim McShane. He is a great guy. I suggest you send him an email


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