NOS Tung Sol 6550 VS Tung Sol 6550 New Production

@jjss49 -     "schubert ....what do u mean .....Never listen to Sylvania 6550s from the 1950s?"      As for myself; that was the question I answered and (as stated), simply with my take on Schubert’s post.        Just a guess; I’ll bet the OP found his tube replacement, long before this dead thread was resurrected.        Not that anything you posted was incorrect, but, at times; dates are also relevant details.

@rodman99999

thx for pointing that out

i mistakenly addressed my comment to tattoo, i meant persephone, who commented just previously 0n 10-28-20 to which my comment was meant to be directed to

Regardless of whether the 6550 is a rectifier tube or a power tube, it has a significant difference in the sonic quality of the Ref 6.  The NOS Tung Sol totally changed the sound--for the worse.  I am sticking with the original Sovtek.

Have numerous KT88s, 6550s. The Mac tube amps from the 60s used either Genelex KT88S or Tung Sol 6550s. To me, and I just recently retired my MC60s, the TS 6550s gave these amps which had tube rectifiers, the most convincing reproduction. 
The new Tung Sols have great dynamics but there is definitely a haze that obscures the voices, but all in all the NOS 6550s caused the least listener fatigue. While running the MC60s, after hearing the NOS Tung Sols I rarely swapped them out.