I just bought Audio Research REF 750s mono amps. I believe it has 21 tubes in ea amp and it has 20 KT150 in ea amp. 40 - KT 150s total. The original set has 600 hrs on them and I also bought a brand new matched set of 40 KT 150s from the seller that he purchased from Audio Research as a spare set. So I will definitely not be worried for some many many years to come.
