You know I am probably not qualified to answer that; I never really spent serious time with either amp using that tube. You should look at the SP amp though; because as Akhilesh says in his post, the DRD is just a way to try and save on OPT's. And I tend to agree with his point. The SP is more like a normal design and heck; if it is good enough for Gordon Rankin. There is no free lunch.