A McIntosh MC275 Mk IV or Mk V would be ideal -- especially since your speakers come "pre-biamped" so to speak.
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this month's Stereophile has an Audio Research integrated that they think very highly of which is priced reasonably; under $5k. OTOH it may not be quite 'tubey' enough to give you that 'change of pace' you desire.
as someone who has your same gear, i have had the same 'temptation' but have never actually scratched that itch. i was always stopped by the realization that unless i go for 'the high priced spread'....a set of used Lamm ML2.1's.....the loss of information compared to the NHB-108 would likely cause me to never actually use the Tube amp much. plus i use the Evolution BNC cables for the 'zeel' 50 ohm interface which make quite a difference too.
you might contact Ruggyboggie who has been using his darTZeel pre with tubed amps for awhile and recently added the NHB-108. the only thing is that he does not yet have the 'zeel' BNC cables so he's not yet in a position to say how the 108 with the BNC'c compares to the tube amp without them.
i still have the temptation to have a set of nice tube amps sitting there i can try when the urge strikes, but every time i get a bit of scratch it gets sucked into tt's, RTR's, or other higher priorities.
I am considering the mcintosh which is well-liked here thanks for the suggestion have you heard it with the dartzeel preamp?
I am tempted with mcintosh mc275 mkv but the folks at hoffman swear by the mc30? I think the mc30 would be more finicky to keep happy even assuming I find a mono pair in good shape. Is the mc275 mkv autobias?
I was also considering the BAT vk55se or the vk60
I think I will stay away from integrated because I love the Dartzeel preamp for line/phono.
I could swing the lesser priced EAR tube power amp too?
Any other less finicky preferably autobias tube amp to consider with 50 watt or more power?
Since my speakers are not high efficiency will stay away from set amp or other lower powered amps.
I would ask Jonathan for his opinion if you have not already yet done so. I cannot respond directly to your question, but note that I have a darTZeel amp and a VAC Renaissance 70/70 Mk. III tube amp that I run with a solid-state, battery-powered Rowland Coherence II preamp. The VAC is a push/pull, 65 watts/channel, zero feedback triode design that autobiases and runs 300B output tubes (it also has a sentry circuit that shuts down any output tube that begins to go outside of safe operating parameters). It is all point-to-point wired, and features very high parts and output transformer quality (ten years ago, the Mk. III retailed for $14K and the Signature version $18K). Mk. III's can be had for between $3K to $4K used. I'm not necessarily advocating this amp - I have no experience running it with Evolution Acoustics speakers - but am simply trying to give you ideas. Again, I would talk to Jonathan if I were you.
with the level of quality of your dartz amp & pre-amp I doubt that a tube pre-amp at under $5000 or even $8000 would give you as much as satisfaction with your s/s dartz amp.
Even though one is s/s and the other is tube, the cheaper tube amp will not give you the same level of refinement as the dartz.
I have tried this route on numerous occasions & it always ends up disappointing. (always to the detriment of the cheaper component.)
Personally I would hold off to that purchase.
However if you would insist, i can highly recommend you give one of those tube lamm power amp a spin. Those have similar level of pedigree as your dartz amp.
I too was a solid state guy and now tubes. To me, like vinyl, tubes are away of life(music). Either you do it or you don't! Any half way attempt will just end in disaster("I tried tubes don't see the big deal" kind of talk)! Happy with dart? Stay the course. Looking for something else? Make the move(or another set up). I did. Not looking back! That is the way I see anyway.
The only "current VAC amp" that is point-to-point wired is the Statement 450. I remain skeptical that it is, overall, equal to or better than the Renaissance vintage of amps. It does not appear to be a triode circuit and it is not biased fully Class A. It's also a high-powered design (i.e., loss of transparency and delicacy) that almost certainly uses feedback (disaster), and the output tubes are pentodes. The Kevin Carter-designed Renaissance amps were all-out efforts from the late 90's, when the company was flush with cash from the great economy and its contract to make the Marantz Model 7 /8B /9 reissues. VAC is still a great tube gear manufacturer and it stands behind what it makes, but those days are gone, I'm afraid.
If you want a real tubey, syrupy sound, I'd look into a used Cary V12R. They're 50 watts triode or 100 watts ultralinear. You should be able to pick up the V12R at under $2500. The CAD-120 mKII may also be worth a look, but I have no experience with it. I can't comment on how nice the V12R play with your other gear though.
My recommendation is the SAS Audio Labs Ultralinear 50 watt monobloc amps. They list for $3500 and are autobias. Steve is a gifted designer and these amps along with his 11A preamp are stellar. His products are also known to work well with other gear both solid state and tube. I havent heard the dartzeel, but I am aware of its reputation. I have heard other very high end solid state and tube gear, and to my ears the SAS will go toe to toe with the best of it. I therefore believe the SAS amps would sound fabulous with the dartzeel preamp and give you that slight alteration of flavor you are looking for. Another plus is that SAS has a 30 day money back guarantee, so, if the sound is not what you envisioned you can return them and try something else.
Jwm: Kevin Hayes is a good guy, but he's a businessman and is not going to say that his current production gear is inferior to his past gear ("Yeah, gee, we don't make'em like we used to"). I know two VAC dealers, however, who can speak to the change in his business model and how his recent production stacks up against the Kevin Carter-era Renaissance amps - according to them, the Phi amps are not in the same class as the Renaissance amps, which makes sense given the Phi amps' cheap circuit boards and pentodes. In addition, an acquaintance of mine had both a Phi amp and the 30/70 Signature monoblocks for long periods in his system, and he found the 30/70's to be the better amps by a good margin. As for the Statement 450 amp, VAC went back to expensive point-to-point wiring, but that amp will have the issues listed in my previous post.
It sounds like you have some listening to do. Many of the recommendations provided have interesting and worthwhile, but they will provide you with different versions of tube-ness.
I have run both solid state pre and tube pre with tube amps for a while. Currently, what spends the most time hooked up is a vintage solid state phono/pre with tube amps. If anything, I may change my amps - not sure if I will go tube or solid state. Having heard my Audio tekne push-pull amps on my main system, I know I am missing something in the 'sweetness'/'lushness' category but I also need more power. May end up bi-amping to get the power on the bass.
In the preamp spot, I can recommend the Jadis JP-80. They are not the last word in detail and transparency but it is a wonderful-sounding tube preamp. Arthur Salvatore at high-endaudio.com has some interesting modification suggestions to improve an already good pre. I have not tried to implement them yet.
Personally, the tube amplification equipment I would most like to try is the Atmasphere line-up. If your speakers do not present an ugly impedance load, you might be able to make the amps work. You might also be able to make the amps work through an auto-former.
You raise an important point concernoing the300bRenaissance/KT88 Phi300.1 comparision. I do believe it was largely a move based on business/economics rather than pure sonic performance alone. Kevin has gotten VERY good sound with the current Phi amps, probably as well as can be expected with pentode tubes, classA/B and using circuit boards. Also multiple KT88s are much cheaper to replace than good quaility 300b tubes for sure(300b do have a much longer life span however). All things considered the choice to use DHT,point to point wire and class A biasing will result in amore pure and natural sound with less electronic/mechanical coloration/signature, but at the cost of less efficiency and power at a given price point. The use of pentode tubes would make it perhaps more flexible in choice of speaker/drive considerations. It just depends(as always) on what your priorities are and what trade offs you`ll except. No design can do it all, and from past threads it`s clear both of these VAC designs have their own group of supporters. I will tell you from personal experience the current VAC pre/amp combo is very very good, but when both the DHT and pentode tubes are both taken to their maximun potential I feel the DHT is just a bit more nuanced and intrinsically musical.
I largely agree, and you raise an important point about the practicality of the two designs. The Phi amps may be better suited for the typical 87 db. efficient / 4 ohm speaker. While the Renaissance amps have excellent power supplies and output transformers, allowing them to drive speakers that ostensibly more powerful designs cannot (Lyric in Manhattan could not drive the big Pipe Dreams with the VTL 750 watt/channel Brunhilde, but was able to easily drive it with the 70/70; another Manhattan shop, I can't recall which, hooked up a 30/30 to a pair of B&W 801N's, a speaker that requires bi-amping with big SS amplification, just for laughs, and it drove the speaker), they do have their limits. That said, on the state-of-the-art, 93 db. efficient MM2's with all-darTZeel electronics that the author of this thread is running (my closest hi-fi friend runs MM3's with all darTZeel electronics - these systems play at the very highest level), this gentleman wants the best sounding tube amp he can find, i.e., full Class A biased, directly heated triode, zero-feedback, point-to-point wired and otherwise featuring top parts and build quality, etc. He also writes that he wants auto-biasing, something that puts out 50-75 watts/channel, and that he can buy used $3,000. A 70/70 Mk. III fits this profile.
Your friend does have high standards and expectations for his price range. But again you`re right , if he can buy a 70/70 amp for only 3 grand that is without any question an outstanding bargain. He would have top tier sound and might prefer it to the much more costly darzeel, any way I`d love to hear that system with acoustic jazz and classical music.