ARC Ref 3: Tung-Sol 6550 in power supply?

I have sourced a new production Tungsol 6550 from The Tube Store in Hamilton (Ontario); I intend to use it in the power supply of my ARC Ref 3. Has anyone had any experience with the Tung-Sol TS6550 in the Ref 3? Have you compared it with the original Winged "C" SED 6550C shipped by ARC with this
line stage? Preferences? Reasons?

Forgot to come back with comments. But I'm back.

Ok, I swapped the ARC 6550 WE tube into my PH-8 and pulled the Tung Sol 6550. Maybe the 6550 isn't as critical in the PH-8 because I am not hearing a world of difference.

I have 3 ARC components that use the 6550 as a regulator tube in the power supply. Hopefully, Kevin will source a more reliable batch of SED Winged Cs when I am ready for a retube.

@Guido -- 500 hours seems kind of a long time for break-in. Can't say that I have had such an experience.

@Elberoth -- gotta say I am a believer about ARC sourced KT-120s. Maybe it's just bad luck, but for some reason, some of Kevin's KT-120s just don't bias as closely in my Ref 150 as those sourced from ARC. Can't say why.
Most interesting Ptcl99 , my regards for your spirit in pursuing your experimentation, especially with your utilization of non NOS valves.

I have an ARC Ref 3 and also a Ref 6, which is the one I use in my main system. I recently bought a NOS Tung-sol grey plate and tried it my Ref 6. (I presume the comparison would be the same in the Ref 3, although I did not try it in this unit.) The original Sovtek had a nice coherent quality—a sweet, rich midrange with an all around natural quality. The NOS Tung-sol had a deeper, tighter bass, more extended highs and was more dynamic. However, the midrange was utter crap—bright and edgy. The original Sovtek was so much better, so I would agree with the people who advise to stay with the original 6550 used. One person mentioned that tubes are biased differently and that may be the reason why some tubes work better in some systems than others; I am not really tech savvy, so I can only wonder if this is the case here. I got this NOS Tung-sol from Andy of Vintage Tubes who assured me that the midrange was outstanding in this tube. Giving him the benefit of the doubt, I wonder if he was referring to how it works in equipment other than the ARC Ref 6. (He probably never heard it used in the Ref 6 and never mentined a caveat on how it might not be compatible with my preamp.) Another person mentioned that the Tung-sols need 200 hours break in time. That sounds excessive; I did a break in for 50 hours and there was some improvement, but not really that significant. Anyway, from someone who has done the comparison of the original Sovtek 6550 and the much more expensive Tung-sol, I would advise to leave well enough alone and stick with the original.

I think my comments on the 6550 tube replacement for the Ref 3 would be relevant to my failed experiment with this in my Ref 6.  I tried the Tung Sol NOS grey plate that was recommended by Andy at Vintage Tubes.  He assured me that it had a great mid-range.  He was dead wrong.  This tube was dynamic, tight, deep bass and extended highs--but the mid-range was utter crap--not musical at all.  I went back to the original Sovtek and this has a rich, sweet mid-range.  The expensive Tung Sol gives you listening fatigue in a very short time.  Stick with the original tubes used by ARC.