Jasper ... my local ARC just left my house. My Ref 150 sounds great!!! Two bias resisters on the same tube blew. No surprise really. The tubes have almost 2000 hours of use on them and they are ready for a replacement. Maybe KT-150s if this stupid KT-120/KT-150 enigma is "officially" resolved.
Your solution is NOT about using more "robust" bias resisters. The problem has to do with arcing inside the tube itself. Although new tubes can arc, older tubes are more susceptible because of the natural process of heating (expansion) and cooling (contraction) that occurs when the unit is turned on and off.
I am dubious that an authorized ARC repair tech will replace a burned/open bias resister with anything other than original ARC spec. It may seem crude, but one of the functions of a bias resister IS to open if the tube arcs. It protects the amp like a fuse.
Your solution is NOT about using more "robust" bias resisters. The problem has to do with arcing inside the tube itself. Although new tubes can arc, older tubes are more susceptible because of the natural process of heating (expansion) and cooling (contraction) that occurs when the unit is turned on and off.
I am dubious that an authorized ARC repair tech will replace a burned/open bias resister with anything other than original ARC spec. It may seem crude, but one of the functions of a bias resister IS to open if the tube arcs. It protects the amp like a fuse.