I have a compu-bias meter. I didn't change the bias at all from where it was which by the way was on the low side of what the manual recommends.
Would you please post back what ARC's service department response to the use of compu-bias meter is.
There is no recommendation to reduce bias before tube installation anywhere in the manual. The amp comes from the factory already biased.
No there is not. But normally as the power tubes age they need to be re-biased as they age and get near their end of life. You never re-biased the 6550 tubes that came with the amp since it was new?
IF you had re-biased the 6550 tubes you would have increased the settings of the bias pots. And that is why you reduce the setting of the bias pots before installing new power tubes. If not you could damage the new tubes.
Just curious after using the compu-bias meter did you ever check the bias setting with a 3 1/2 digit meter to see if the bias was set at 60mVDC, (.060 Volt DC), as per ARC specs?
As for running the bias below the recommended 60mVDC I can't speak for the VS60, but I can for the ARC VT50 amp using 6550 power tubes. ARC specs 65mVDC. If the bias is set at ,say 60mVDC the SQ loses upper end detail and the bass is not as tight. Midrange is softer. The Amp sounds best when the bias for each channel is set at 65mVDC.
As for the ARC manual,.... ARC leaves a lot to the imagination, imo. I think ARC figures if you are buying one of their amps, that is not an auto bias amp, the user must therefore know how to bias the amp.
I bought my ARC VT50 new in 1997. No where in the manual does it say anything about biasing the 4) 6922 tubes in the amp when re-tubing the 6922 tubes. But they do have to be....
Hard to believe you never checked/reset the bias on the 6550 tubes that came with the amp.