$20k(ish) tube preamps

I would call McCormack audio, the VRE1 Pre is astonishing. 
 

A Supratek or a Don Sachs will compete with $20,000 retail preamps.Except they will cost a lot less because you can buy them direct from the makers and avoid large wholesale and retail mark ups.The Suprateks also come with a lifetime warranty.

There are some really excellent pre-amplifier designs and I have come to the conclusion this piece is often overlooked and can often be a bottleneck in the signal path.  I now believe it is even more important than the amplifier.  Once you narrow down what you desire, hifishark.com is your friend.  

No support for the VAC Master? i'm surprised as it's on my short list, tied to my Gryphon Antilleon EVO stereo. Not trying to hijack the thread, but any thoughts on the Master?

I love mine but the Master retails at 28K (possibly more now?), and 40K with phono stage. A used one can come in under 20 but I don't know if that meets OP's criteria. It's definitely a great match for powerful Solid State amps and high power tube amps. Has the classic "romantic" tube sound, while also being extremely articulate and refined. 

I also like my ARC Ref 6 a lot, and the 6SE should be even better. 

You won't do better than an Allnic L9000.

https://soundstageultra.com/index.php/features-menu/opinion-menu/106-uncategorized/1031-allnic-audio-l-9000-otl-ocl-preamplifier

I've been running an Audio Research Ref 6SE for a little over a year and I couldn't be happier.

What are you replacing?

No support for the VAC Master? i'm surprised as it's on my short list, tied to my Gryphon Antilleon EVO stereo. Not trying to hijack the thread, but any thoughts on the Master?

You should also consider the Nagra Classic in that price range.

They have a great phono stage besides the line stage.

Convergent Audio Technology ( CAT )Black Path, or a used older model like the Renaissance.

From my point of view (with my tastes)I would look at anAudio Research Reference 6SE. My system is all ARC Reference components… I have never owned or heard a more pleasing detailed and natural sounding system.

after a certain price - there are almost no improvements ... (only a case made of gold and ivory).

buy yourself a CAT SL -1 and you will be happy ... give the rest of the money to the poor (buy them new things, education or medicine) ... otherwise there will be no happiness ...
It is best to do this secretly and not tell anyone.

Call Tom Vu at Triangle Art Audio.  The L200 is really good.  

Atma-Sphere MP-1.

At your budget, you can add the Caddock resistors, and just about all the 'upgrades'.

Though Ralph Karsten is the manufacturer, I would either call or PM him (atmasphere), to get his take on this. He knows just about all that is available, and can give you accurate information, sans bias.

Bob

Absolare Preamplifier.

Audition a Zesto Leto Ultra II   , they make great tube preamps 

I heard the CL-1000 at my dealers store. It is neutral and very detailed. I heard the preamp hooked up to the Luxman 300B tube amp. Excellent combo. It's similar to my CL38U SE but is a few steps quality wise above mine. There is someone on Audiomart selling a CL-1000 for $6000 off the regular price.