I also have the ARC Ref 6 and thought I would try the NOS Tung-Sol. I like a rich, sweet midrange, which is what the stock Sovtek has. I did not like the Tung-Sol. It has more extended highs, a deeper, tighter bass and is more dynamic. However, the midrange is sacrificed for these qualities--all in all I did not find it musical. I much preferred to original Sovtek; it has a very sweet, rich midrange. I thought there might be an issue with break-in time, so I did put 50 hours on the Tung-Sol with only a slight improvement.
NOS Tung Sol 6550 VS Tung Sol 6550 New Production
Has anyone had experience with the new Tung Sol 6550 new production power tube. If so how does it compare with the NOS Tung Sol 6550 ones. I want to replace my stock Sovtek 6550 in my ARC Ref 6 . But from what im seeing the NOS Tung Sol 6550 is way up in price of about $ 350. And the new Tung Sol 6550 new production power tube is about $ 35 from the Tube Depot.