Just found this on another site.
No mention of pricing
ARC amps and KT150's
Audio Research finally clarified this morning in writing that the KT150's are electrically compatible with the following:
VSi60
VSi75
REF75
REF150
REF250
REF750
However, because the KT150 is physically larger than the KT120, technical compatibility has not been confirmed at this time. For example, they indicated there might be a "clearance problem" with the top cover of the REF75. MEP can you confirm?
There should not be an issue with the REF150 or REF250.
They made mention that the proper selection of the bias range and device matching of the KT150 tubes for each model is of critical importance for optimal sonic performance. They recommended customers purchase properly matched and biased KT150's from Audio Research for their particular product - when they become available from ARC - later in the first quarter.
They mentioned that KT150 tube sets will not be available for the REF750's for quite a while due to the tube matching requirements for a pair of the big 750's.
ARC made mention that they will NOT be held responsible for damages and/or repairs to a product if the KT150 tubes were installed that were NOT purchased as a set from Audio Research. Interesting.