Audio Research VSi60 integrated reliability?

ARC amps do not explode. Occasionally, if an output tube arcs, a resistor might blow which is what it is supposed to do.

Well KT120's arc just like 6550's do. Possibly a bit less often. With regard to the Chinese 6550's of decades ago. Frankly they were awful tubes. But that was all that was available. They looked like the Tung Sol coke bottle 6550 but that's where the similarity ended. Their failure mode allowed the heater to work but not much else. The light was on but no one was home so to speak. I'm guessing in the D-125 more than one tube arced at the same time. The Chinese tubes liked to do that back then. The only Chinese tubes I will use even today are the EL-34 Treasures. That's it. Once bitten twice shy. Remember, at the time the Chinese were making the 6550, the Russians were still trying to gear up to make one. ARC helped the Russians make the 6550. I just wish they hadn't initially used the GE 6550 as their model. I always thought the Philips Sylvania 6550 was a much better tube. Initially the Russians were trying to change one of their stock beam pentodes into a 6550 but that failed miserably. The Russians never stopped making tubes. Remember, the Winged C 6550 was probably the 12 version of the Russian 6550. Trust me, I saw every single version of that tube over the years. Some good some not so good, and some without any getter flash at all. The KT-120 represents what is considered to be state of the art in Russia. The KT-120 looks to me to be a modified version of one of their radar tubes. It's a winner.

I would not blame ARC but rather the tube manufactures. Quality is up and down. Since you have the choice of 6550's from Russia or China, I choose Russia. Tubes are not at all like transistors. Once a tube is on, it's going downhill. Some blame also goes to the consumer. When ARC says their output tubes are rated for 2000 hrs. they mean it. I can't tell you how many ARC amps I've seen that were abused. When your 2000 hrs are up that doesn't mean to wait till a tube arcs to replace them. It also doesn't mean if one tube fails, just replace that one tube. It also doesn't mean if the fuse blows, up-size the fuse. When you buy a Ferrari, don't put regular unleaded in it. Any tube amp from any manufacturer can arc a tube, it's the nature of the beast. Treat it well, and it will last many lifetimes. Abuse it, and it won't last long.