Tube amps

I've decided to upgrade my current SS amp (McCormack DNA 0.5) for a tube amp for use with my Wilson WP6 speakers. I am looking for a little more warmth in the midsection and think that tubes may be the way to go.

My budget is around $2000 used and so far I'm considering the following candidates:

1) BAT VK-60
2) Cary V12i
3) Primaluna 7

I would appreciate any comments or opinions anyone might have on this.
The Cary V12i is a sweetheart and I think your WP6 would appreciate its extra power over the other two candidates. This is not to be underestimated if you want to have accurate dynamic range, which with speakers like those, I'd hate to compromise.

Conrad Johnson premier 11a or MV60.
It's the speakers which lack the warmth
While the WP's are nominally efficient and marketed as being tube amp-friendly, they require an amp that can produce a lot of current to control the woofers (the impedence on WP's drops very low in the bass), which rules out the vast majority of tube amps if proper bass performance is important to you.

The CAT stereo amp will definitely work (it has monstrous output transformers and can drive 2 Ohm loads). Even at used prices, however, it exceeds your budget. If you have to do it on the cheap, maybe (MAYBE) the Sonic Frontiers Power 2 will work (Power 3 monoblocks would be better), but I have not personally heard that amp on Wilsons.

The safer bet, due to the WP's current requirements, is a really fine solid-state amp. The Rowland Model 2 has a pleasing midrange, very high transparency and great build quality, and assuming the rest of your system is up to the task, sounds particularly good if used with the optional battery power supply and run balanced.

While many tube amps can make sound come out of WP's, few can control its woofers properly -- you need to be very careful pairing a tube amp with those speakers.
It was my understanding that tube amps are better at handling low impedance loads - am I wrong?
I agree with the other posters above. I have WP7's and while they are voltage efficient at 92 db/watt, they are a difficult load in the bass. I tried some 15 wpc SET Cary Audio amps and the bass was flaccid and the dynamic range was compressed. Nice on voices and acoustic instruments but poor in bandwidth and dynamics. I then powered them on Conrad-Johnson Premier 140 and Audio Research VT100 Mark III tube amps, which are quite neutral tonally and sounded terrific on the WP's. Yes, they gave up some of the bass impact and dynamics of the best SS amp I have heard with them, an Essence Emerald II, but there is no beating tubes for warmth and dimensionality. I thought the C-J and ARC amps to be the best middle ground between typically dry and flat SS, and warm and dimensional tubes. Of the amps you list above, my gut feel says the Cary amp because of its multiple output tubes and probably lower output impedance, but I really think your best bet is one of the larger push-pull tube amps or a really good, powerful SS amp. The dynamics and bass of my Essence 250 wpc SS amp must be heard to be believed. The trick, as always with SS, is finding one that has some of the dimensionality and warmth of tubes. There are getting to be more of these recently, so maybe a good SS amp from C-J, Pass Labs, Jeff Rowland, or even a used Essence amp might be the trick.
Tube amps are usually not as good at handling low impedance speaker loads due to their high output impedances. A typical tube amp output impedance is about 0.5 to several ohms, while solid-state amps can have impedances down to 0.01 ohm, depending on many factors including global negative feedback. Because of this, SS amps usually have more control in the bass frequencies.
I have been using a Music Reference RM200 for over four years with my WP7s and have found it to be an outstanding combination. The RM200 has an extraordinary ability to deliver power to relatively low impedance loads, such as the WP7s. In addition, it has proven itself to be extremely robust and trouble free. They can be found on Audiogon for $1.7k to $2.2K.
I have paired WP 5.1 with SF Power 3 before. Despite the power rating, SF Power 3 was not able to drive the WP 5.1 without clipping. WP6 might be an easier load than 5.1, but I doubt it is very different. But if you want to go the tube route, I will suggest SF Power 2 over ARC VT-100 II if you want to stay within your budget.

Tarsando is correct about WP 6 is why the sound lacks warmth. If your goal is to have warmer sound, start with new speaker search.
Of the original options,the PL gear would be the first choice.A VAC Ren series amp is a good match and has adjustable feedback,so damping of the woofer can be controlled.
A few comments in response to the above posts ...

I owned a VAC Renaissance 70/70 Mk. III stereo amp and have owned continuously in my main system for the past six years VAC Renaissance 140/140 Mk. III monoblocks. Even the stereo 70/70 is a very powerful amp that can drive 2 Ohm loads (it is totally dual mono, all the way down to separate power cords and on/off buttons), and all Renaissance amps have very high quality output transformers and beefy power supplies, which are the two things needed for high current delivery. That said, I respectfully beg to differ from the above post on one crucial issue: while the Renaissance amps do have a variable feedback control, if you have to use it, then buy a different amp. Triode amps don't sound right when run with feedback (or more accurately, they sound like just another amp when run with feedback).

As for the PrimaLuna, not even their monoblocks will work properly with WattPuppies because, at 37 lb. per chassis, they do not have anywhere near the kind of output transformers and power supplies required to drive low impedences properly. VAC's Renaissance amps weigh 135 lbs. each and CAT's amps weigh 192 lbs. each for a reason -- very heavy-duty, high-quality output transformers and lots of power supply capacitance. With the possible exception of Antique Sound Labs, all of these cheap Chinese tube amps are indeed too good to be true.

With speakers that need a lot of current like WattPuppies, it is possible to do solid-state amps on the relative cheap and still get good sound and proper bass control. With tube amps, however, there is no way around spending a lot of money because the output trannies and power supplies needed to do the job are extremely expensive (for example, the 70/70 cost $14,000 ten years ago and the CAT stereo amp costs about the same).

Will a given tube amp work on a given pair of hard-to-drive speakers? If it takes two people to pick it up and it costs as much as a new Honda Accord, the answer is yes.
I do apologize,I gave a readers' digest condenced reply.The Vac is a far superior design to any of the posters' options.That said,there are issues with the other options that I did not want to delve into.If VAC/Dennis Hadd had felt that it was a liability to allow a db or two of feedback,I'm sure he would not have provided the control.As all systems vary,it is a practicle option and possibly a valued one for all but the purist.
I don't think one VK 60 would have enough power to drive the WP's. But, with a pair of VK 60's I think you would be pleasantly suprised. If you had those amps converted to monoblocks they have zero negative feedback, and the output transformers and power supplies to handle the low impedence loads that would be thrown at them. I think this option is very economical at less than 1/2 the cost of a VAC or CAT. Don't get me wrong the VAC and CAT are exceptional but the BAT can deliver the current and power as well.
Not to belabor the issue, but Kevin Hayes is VAC and Dennis Had is Cary. The feedback control was included on the VAC Renaissance amps more for marketing than anything else -- even 1 db. of feedback takes away the magic on dynamic-driver speakers (feedback can help with stats, however).

PS - It is my understanding that the top BAT tube amp (the "SE") is a very fine amp -- I was too busy reacting to the idea of a cheap (PrimaLuna) to modestly priced tube amp (Cary V-12) on WattPuppies to notice that BAT was one of the listed choices.
Jensmunk, After reading your post again I need to clarify my response. One VK 60 might drive the WP's. With the information you provided it's a difficult question to answer without more information. How big is your room, do you listen to lifelike volume, what type of music do you listen to, and are to willing to sacrifice chest thumping bass? With this type of information you might be able to stay within your budget. BAT has paired up with Wilson at numerous audio shows and is very familiar with the product. You might give the folks at BAT a call as well. Good luck in your journey.

My room is small (13X16) and I don't usually listen to music at very loud volumes (my wife may disagree). I am generally not a bass freak, and enjoy folk music, as well as Mark Knoffler, Van Morrison, EmmyLou Harris etc...

On another note, I've been looking into the output impedance of various tube amps and the BAT is particuarly high at around 8 ohms. On the other hand I actually have a CJ Premier 11A, which I am using in a second system, and its output impedance is only .5 ohms. This would seem a more reasonable match for the WP6's where the impedance dips near 2 ohms at low frequencies.

Both of my other original choices also have relatively high output impedances.