DOA tube from Audio Research
ARC VS60 DOA? The filament is open? The tube arced and shorted out? If so did you back off the tube bias adjustments before installing the new power tubes? ARC VS60 manual . |
compu-bias meter Dfwlistener, Would you please post back what ARC's service department response to the use of compu-bias meter is.
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. . |
Dfwlistener, The power tubes that were shipped with the amp are the tubes that were used to bias the amp. By chance did you ask Kal, of ARC, after the new 6550 tubes were biased for the amp does the bias ever need to be checked or readjusted? Do the power tubes need to be checked for proper bias after say, 50 hours of use, or 100 hours of use, or maybe 500 hours of use? Or even 1000 hours of use? I suggest you call or email Kal and ask him about checking and readjusting the bias of the power tubes as they age from hours of use. Like I said in an earlier post the user ARC manual leaves a lot to the imagination. As for your original post I assumed you were replacing the power tubes because the old tubes were near their end of life. (Approximately 2000 hours of use). If that was the case and normally the user of the amp would have reset the bias of the power tubes as they reached their end of life, before installing new fresh power tubes the bias pots should be turned, adjusted back, before installing the new tubes. Ask Kal if you contact him again. Some reading material for you. What is the Bias Point? >>>>>>>>>> Quote from Link below. When installing fresh power tubes, you have to remember that your old tubes likely required less negative bias to maintain the same idle current as they aged. Before plugging in your fresh set of power tubes, you may want to adjust the bias so the reading on your meter is lower before plugging in the new tubes!Upscale Audio FAQ . |
