2. amps-preamps
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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
8 responses Add your response
ether OP
63 posts
 
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!!
yogiboy's avatar
yogiboy
5,661 posts
 
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?
ether OP
63 posts
 
I know about the warm up.... this part was clear to me....however, when the manual says the amp should be under no load  - I thought they meant nothing connected.

The tubes are new and matched from TubeDepot and burned for 24hrs
jea48
4,425 posts
 

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.
.

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


yogiboy's avatar
yogiboy
5,661 posts
 
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.
ether OP
63 posts
 
thanks for the answer - so I should keep speakers connected but disconnect the interconnects for preamp when adjusting the bias ?

The ARC manual says to perform the bias adjustment with no load....so I assume they mean no speakers and no source.
yogiboy's avatar
yogiboy
5,661 posts
 
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.
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