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!
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Showing 3 responses by yogiboy

Never disconnect the speakers. Most tube amps need a load when turned on! You should not worry about a few mv's with the tubes.
I just took a look at the manual. You don’t have to disconnect the preamp.Just turn the volume down so there is no signal. Always keep the speakers hooked up or you will damage the amp! Where does it say to do bias adjusment with no load? I don't see that.
The manual does not say no load. Where do you see that? It says zero signal conditions. Do you have a different manual than the one that has been posted?