Why does this old tube gear sound so good?

I have a realtively modest system...Rotel cdp feeding an MSB Link dac, Sonic Frontiers SFL-1 Sig preamp with Telefunken 12at7 tube, Classe 10 amplifier driving North Creek Music Borealis speakers....Kimber and Cardas cables.

Every once in a while I pull out some vintage tube gear that I have collected...in this case a McIntosh C-11 tube preamp and a pair of McIntosh MC-60 tube amps.

I carefully insert the Mac stuff, make sure connections are good and everything fires up OK, and then.....magic.

The normal gear doesn't sound bad by any means, but with the Mac gear it just sounds more like music, more alive, robust and palpable. I know this has been discussed hundreds of times before on this forum, but I am always surprised by how good this 50 year old, original condition gear sounds.
Because it is!
I am not surprised at all by your preference for the Mac gear. My question is why do you use your "normal" gear when the vintage eqpt sounds better?

I'm sure the Mac gear you mention sounds very nice. In contrast to your SS Classe system it is certain to provide a markedly different sound. I wonder if that difference might be more a matter of tubes vs ss, as opposed to 'old' tube gear sounding best. Have you tried other, more modern tube kits and compared them to the Mac stuff? You might like a whole variety of 'newer' tube gear as well, perhaps even more than the vintage Mac stuff. I guess my question is, on what basis are you concluding the that it's just "old" tube gear...what else have you compared it to?

Tubes are an old and mature technology. As a result, tube based technology has been good for a long time, if implemented properly. And I believe it is generally accepted that early Mac equipment was well engineered for its time. I don't think it would be as good as state of the art modern tube gear, but it should stand up very well to lesser, modern gear. You should use it and enjoy it.
I have been told that the old tube output x-formers are "better" than the newer ones. Same thing with the older oil capacitors, which, I believe, contained PCB's...now banned.

I'm not sure if this is true, but hobbyists will pay BIG BUCKS for these parts...much like for NOS tubes. I have experience with NOS tubes, and I can assure you that modern tubes do not have the fidelity or the longevity of NOS tubes.
Everybody's on the mark hear but wonder what you'd think of the newer tube gear say newer mac tube stuff?Would it have advantages in lack of distortion yet still have that "good" upper harmonic distortion which is essentially what we like about tubes?You should go listen and see what you think.And maybe you sell this primary set up and your classic stuff and get one set up of updated classic gear.
It's been speculated that transformers continue to improve through decades of aging.
Interesting...have you considered that your "modest" but newer gear might not be suited to your high quality taste for vintage sound? Alternatively it may be either the euphonic tube soudn or the way the tube output transformer reacts with your speaker load (EQ's the presentation to give an emphasis at 50 Hz and at 1 Khz, according to your speaker impedance plot).

Your speakers are excellent but they clearly do not suit your taste if they don't sound lifelike with your existing setup, IMHO. Try the tube setup for a few days with a variety of source material and see if you eventually find it tiring with the emphasis at 1 Khz. If you end up always preferring the old mac tubes then either your room is too dead or the speakers don't suit you. Just two cents....no offense intended.
obviously you have answered your question. welcome to tubes. old or 'new'... just more 'organic' musical reproduction. ss is great but, IMO, does not really sound as 'live' as tubes.
Thats because musical satisfaction and emotional involvement has not in any case to do with a perfect frequency response or top notch measurement values...I really love my Paragon 12A preamp from the late 70's which sounds magical to me, because it has almost the same analytical qualities as my Gryphon amps but gives every note more sense and puts everything more in the right context.
Sonic Frontiers SFL-1 I had at one point is a pretty solid state, neutral at best sounding Preamp.. The TUBEY sounding Tube gear of the mcintosh is not that shocking honestly.. Try running even just the Mcintosh Preamp without the Tube amps, or the Tube amps wit the SFL-1 and you will have even further varying results.. it does not all have to do with New vs. Old.. just they type of flavors certain vintage or product has.