Audio Research Tube AMP Reliability

well I suggest you contact the people who worked on it to go through the amp again and check the amp for proper output at clipping as this doesn't make any sense...

The biggest problem isn't the fault of ARC. They rate their 6550's life span to be approx 2-3000 hrs. That being said most people don't keep track of the time they put on their tubes. A few ARC amps have Hobbs Meters on them (elapsed time on the tubes)which makes it easy to determine when a new output tube set is needed. As with any high current high voltage tube amp arcing can happen across a circuit board trace but this is usually not the norm. Most of the time a plate and/or screen resistor will open and require replacement prior to installation of a new output tube set and rebiasing. Remember, once that amp is on and the tubes are drawing bias current the clock is ticking.

I repair ARC on the west coast...Non ARC output tubes are always a very bad idea and should never be used.

Most people do not want to spend the money for ARC tubes as they are expensive. I won't fix an ARC amp unless I can use ARC tubes pure and simple. I have had way too many problems with tubes from other vendors and it becomes a huge headache. And yes, it can definitely cause a reliability issue.

Well your bias difference is odd..What did you mean by "blast". Did a tube arc? Bias can fluctuate depending on your line voltage and the accuracy of your volt meter. BTW its 65 mV not mA as you are measuring across a resistor not in series with the resistor.

That's a shame as the D125 is a very nice sounding amp. Being so far away from the U.S. makes it rather difficult to get parts/service etc.

The M-100 run very hot you might want to put a fan on em. Can you still get the 7119's from ARC?

amperex?

Well I havn't gotten in too many M-100 but if I do I know who to call...8o)