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Audio Research VS 115 bias Adjustments

Any A-goners familiar with setting bias on the ARC VS115 power amp??

Just checked and set the bias on my VS115 amp. For those who are familiar with the process on this amp, I checked and adjusted the 4 "Set" ports to 65mV, as specified. However, the bias readings from the other 4 "Check" ports ranges from 63-71mV. While technically in "spec" (i.e., 57-73mV for the "Check" ports), I would have thought the range of bias readings from the "Check" ports would not have been that much. As you know, the bias voltage for the "Check" power tubes cannot be adjusted.

As an aside, I only use ARC matched tubes.

Does anyone know whether the range of bias mV readings on the "Check" tubes is normal (whatever that means) or otherwise could result in a denigration of sound??
bifwynne

Showing 2 responses by lostbears

lostbears's avatar
lostbears
538 posts
 

Are you using 6550s, kt88s or the new kt120 tubes? But that is normal. I tend to move my tubes around so that they are as closely matched as possible. Are these new tubes that you just installed? If so the bias will drift a little as the tubes break in. It is best to check the bias often for the first couple of days.

BTW I like to set my bias around 63 mv on my ARC amps.
lostbears's avatar
lostbears
538 posts
 

The lower the bias the longer the tubes will last. But the amp will not sound quite as good. I think the sweet spot is around 63 mv. I would not go much below 60 mv.

I believe the VS 115 is now shipping with the new kt120 tubes. I know that the Ref series amps are. According to ARC the kt120 tubes are a better sounding tube that will also increase the power roughly 20%. I have not tried them yet but plan to the next time I retube. They are not available seperately from ARC yet.
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