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 3 responses by ether

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.
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
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!!
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