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In Reply to: M60 autobias posted by Ajy55906 on March 25, 2006 at 09:59:13:
A quick rundown:1) Yes and No - No more than the standard bias/dc arrangment will offer clues that a tube has failed, by the sudden presence of a DC offset where there previously was none. The autobias amps still have a manual DC offset control & meter.
2) Yes. It's autobias in the same sense that the McIntosh MC-30 (and others) are autobias - that is, it supplies a calibrated, fixed grid voltage that also tracks changes in the the AC line voltage. Cut the tubes to half, and bias voltages remain nearly constant.
3) Yes. Any 6AS7 based amp can be converted to the autobias method, irrespective of age or state of update.
4) No. It is not a sonic upgrade.. it is primarily a convenience feature. If you are familiar (and comfortable) with adjusting bias & dc on your current equipment, there is no real advantage in going to the autobias method.
If you own Atma-Sphere equipment, you know that despite the relatively high tube count, that bias is generally quite stable. Normally, it needs to be checked and adjusted a few times after a new set of tubes is installed. and then perhaps once or twice a year after that.
Problem is, as the tubes head in to their last 15-20% of service life, the bias current starts dropping off - and naturally, some tubes are in worse shape than others. Owners start cranking up the bias to compensate, and this can lead to an eventual failure (arc-over, etc). The auto bias method holds the bias in a range that is suitable for nearly the enire life of the tube, and avoids the undesirable end-game moves as illustrated above.
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Follow Ups
- Re: M60 autobias - Legendre 16:44:52 03/27/06 (0)
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