Your amp was voiced with Winged C 6550's. Not a big fan of any KT-88's in an Audio Research Amp. As I said in another thread, I don't believe your going to get 2000 hrs. out of that tube. My suggestion would be to wait, if possible, until the KT-120's are available. A far more robust tube for the VT-100MKI. I will need to check with ARC and find out if that amp can run on the KT-120 and if there's enough room in the amp for them as the KT-120 is taller then the 6550. KT-120's draw more heater current but you would get more power out of the amp. When was the last time the front end tubes were replaced and re calibrated? That will make a big difference in distortion products.
