NOT up to par with NOS 6550
I've A/B'd these several times with NOS Tung-Sol 6550s and RCA-branded Tung-Sol 6550s (tests were blinded with the help of a buddy) and they do NOT sound the same as the NOS tubes as another review claims. The reissues are slightly darker sounding and lack some of the detail and high-end sparkle heard with the originals. The amp used was a 70s Traynor yba-1. I much preferred the clarity and evenness of the sound from winged -C- 6550s, though they don't quite capture the warmth of the NOS Tung-Sol 6550s. These aren't bad tubes, but I found the winged -C- to be less muddy and preferred them overall to the current production Tung-Sol tubes. I rate them a 3.5, the winged -C- would be a 4.5, and the NOS Tung-Sol get a rating of 5 as they are the best I've heard so far.