Big amps, but this problem is not a huge problem. A fried resistor and maybe a failing tube took it out. Personally, if it were me (and I am capable for diagnosing and repairing this type of equipment), I would find a local authorized Audio Research Repair facility and take both amp in for repair/checkup.
In LA, there are a places and people authorized by Audio Research. You don't necessarily have to ship the amp all the way back to Audio Research.
Part fail. it is a fact of life for mechanical and electrical devices. but, it isn't the end of the world.