Japanese tube amps. Wavac, Air Tight, Audio Tekne, Komuro etc.

Air Tight is very highly regarded, but probably gets more discussion on sites other than Audiogon, just as do other highly regarded tube amplifier brands, thinking Jadis, VAC, NAT, Nagra, Margules. Air Tight enjoys a reputation in tube amplification similar to what Accuphase enjoys in solid state.

Yes, many high end brands are not discussed here or discussed very little. I don't know why. I can understand that not many have one of those Japanese amps or Nagra but still. Even VAC and Lamm are rarely talked about. Accuphase, Gryphon, Soulution etc, - sometimes but again not much. They are all expensive and very expensive equipment, of course, but I don't think that's the main reason.

Add Aesthetix to the seldom mentioned list. Top quality stuff.

I owned an Air Tight ATM-2, which was used to drive Harbeth SHL5+ speakers. It was the best tube amp I've ever owned; the sound and build quality are exceptional. 

I'd love to pick another ATM-2 up someday, but you rarely see good quality units on the used market. 

I liked the lower powered offerings of the likes of Shindo, Kondo, and Yamamoto.  Some of the older Kondo gear, like their M10 preamp, are stunningly good sounding.  I sort of found that out the hard way.  Many years ago, I was in the market for Stax Omega II headphones.  I heard them at a dealership and bought a pair with the Stax tube amplifier.  When I listened to them at home, they sounded good, but not as good as they sounded at the store.  When I asked the store owner about this, he explained that when I auditioned the headphones, they were hooked up to a Kondo M10 and I don't have anything nearly as good in my system.