Micro- you have no such knowledge on my amp and this experience.
1. ARC tube went after a few thousand hours - it wasn't a faulty tube
2. New tubes inserted and the unit wouldn't bias properly as a resistor was blown - this is very common among ARC amplifiers as they have no auto-bias circuit. Ask any technician, including the one who did my warranty service
3. ARC was on a Torus with automatic voltage stabilization - and my voltage never gets below 119 to begin with as easily discernable from the LED display
4. The unit has a dim light and the power meter was taking an hour or two to function, so I assume there is another issue that was caused by the outtage and the tech is fixing
So with all due respect, maybe you shouldn't jump to conclusions.
Once you give us the details we are able to figure exact things. My comments did not address just only your specific amplifier, but what happens generally with some ARC amplifiers. I have owned ARC REF150, REF250 and REF750 and for more than thirty years have been talking regularly about ARC technical matters with our official ARC technician and often exchanged faxes Lev from the ARC service department. I think we have many ARC users here and they may enjoy such comments.
1. Although you only give your general comment on tube age "few" is qualitative and useless information - but IMHO when a tube that becomes faulty because of excessive use it is still a faulty tube. Perhaps not your case.
2. In general the bias resistor opens because the tube was faulty. Surely if you replace the tube without replacing it the resistor the new tube usually breaks or burns the cathode resistor. And no, fortunately 2 is not common and is not related to auto-bias.
3. Nice to know your Torus is a model with automatic stabilization - most of them are not.
4. My point is that a problem with the meter was not an impeachment to listening.
For many years, particularly during the years that chinese tube reliability was very low, I have serviced my Audio Research gear - faults were typically the same as today. BTW, during a short period during the ARC ownership transition, ARC put all their service schematics online - with their help it is easy to understand the usual problems.
BTW, sometimes the cathode resistor/ tube burned due to a manufacturing problem with the coupling Teflon capacitor - it was an issue, quickly solved, of some amplfiers of the ARC 75/150/250 series.