ARC Ref 6 tube replacement

Looking to replace stock tubes in my Ref 6. Anyone replaced their stock tubes? I also heard that that the NOS Tung Sol 6550 is an excellent tube for the power supply. Anyone have knowledge of this? 
I replaced in my REF 3 the small tubes by 6H30P-DR super tubes and the one in the powersupply by a NOS Tungsol 6550 blackplate , the are no better replace tubes imho . 
hansk46 .... Do u mean there are no better replacement tubes than those you mentioned? If so can you explain the difference in sound with the NOS Tungsol 6550 blackplate compared to stock power tube? 
The Ref 6 uses 6H30P tubes, which is a Russian tube that has no substitute.  The older DR version is considered to have better sound, but they are very expensive and rare.  So unless you're willing to pay the price for the 6H30P-DR, there's no tube rolling for the Ref 6, except for the 6550, of course.
hello tatooedtrackman , I got the suggestion from the tubedepot some time ago for replacement of the blacklabel , they suggest  the SED 6550 black sable . My tube replacement for the REF 3 by the blackplate tungsol gave me the following impression : bass tighter , more refined and more resolution .
hansk46 .....Thanks for your suggestion. I also thought about trying the SED 6550 black sable. Was also wondering about the NOS Tung Sol compared to the new remake Tung Sol 6550.