Bifwynne:
I was in your camp as of the spring. ARC had been life testing for a very long time, but I had 2,000 hours on my tubes and wanted ARC's blessings for the KT150s in my Ref 150. I called Kal who indicated that life testing was not complete and that ARC had not passed on the combo yet. So I, being the conservative type, ordered a new set of KT120s from ARC. Then after reading all of the plaudits on Agon, I pulled out my KT120s after only 500 hours and installed matching KT150s sourced from Upscale Audio. It is a worthwhile upgrade. I am convinced for reasons that I am sworn not to tell, that the KT150s will not harm my amp now or ever. If I could do it again, I would have purchased the KT150s in the spring. The difference between the KT150s and the KT120s are similar to the upgrade from 6550s to KT 120s. A little better all around, especially in the low end.
I too suspect that the difference between the Ref 150 and GS 150 is purely a matter of form. In fact, ARC engineers were told to, in essence, fit the Ref 150 into the GS 150 chassis. In the interim, the KT150 tube was released so the GS 150 was modeled around it. My intuition tells me that the layout for the circuit in the Ref 150 is the preferred layout and the layout for the GS 150 is driven more by the new chassis configuration than anything else. Is it possible something was learned and gained along the way in the new design? Absolutely. It is also possible that, with a truncated circuit path, we may have lost something as well.
I was in your camp as of the spring. ARC had been life testing for a very long time, but I had 2,000 hours on my tubes and wanted ARC's blessings for the KT150s in my Ref 150. I called Kal who indicated that life testing was not complete and that ARC had not passed on the combo yet. So I, being the conservative type, ordered a new set of KT120s from ARC. Then after reading all of the plaudits on Agon, I pulled out my KT120s after only 500 hours and installed matching KT150s sourced from Upscale Audio. It is a worthwhile upgrade. I am convinced for reasons that I am sworn not to tell, that the KT150s will not harm my amp now or ever. If I could do it again, I would have purchased the KT150s in the spring. The difference between the KT150s and the KT120s are similar to the upgrade from 6550s to KT 120s. A little better all around, especially in the low end.
I too suspect that the difference between the Ref 150 and GS 150 is purely a matter of form. In fact, ARC engineers were told to, in essence, fit the Ref 150 into the GS 150 chassis. In the interim, the KT150 tube was released so the GS 150 was modeled around it. My intuition tells me that the layout for the circuit in the Ref 150 is the preferred layout and the layout for the GS 150 is driven more by the new chassis configuration than anything else. Is it possible something was learned and gained along the way in the new design? Absolutely. It is also possible that, with a truncated circuit path, we may have lost something as well.