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.
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!
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!
8 responses Add your response
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 |
Like others have said the amp needs to be warmed up before attempting to bias. From ARC Bias instructions: For best results, operate and adjust the Reference110 at120VAC. Adjustment must be made under zero-signal conditions after at least 15-20 minutes of uninterruptedstabilization time.http://www.audioresearch.com/ContentsFiles/REF110_BiasAdjust.pdf If you are/were listening to the amp you need to let the amp set without any signal, music, playing through it for at least 15 minutes so the amp can stabilize. Muting the preamp works good. . |
thank you guys for correcting me and helping me here.... In fact once I left the connections on and just muted the pre-amp, I was able to bias the amp with much better results....all the tubes came tight at or very close to 65mVDC and the measurement were very stable..... Only 18hrs on my new tubes and will try again at 50 and then 100hrs.... I hope after that I can leave it for at least another few hundred hours of play... thank you!! |