Tube amp for "difficult" speakers,,,

I have a pair of Consequence Dynaudio, mk 2. They work well with my s-state 2x600 watts amp and sounds great esp at large volume levels. But I want to switch to tubes, and even triode if possible. Is good tube amplification unrealistic with these 83 db sensitivity speakers? I am probably not the only one with somewhat "difficult" speakers so all advice is welcome.
Since tube amps are more sensitive to overall load than most solid-state amps, it is better to know not only the speaker voltage sensitivity of 83 db/watt/meter, but the impedance load. A lot of speakers with low voltage sensitivity are relatively easy loads, so all you really need for a good tube amp match is a fair amount of output power. Conversely, you can have a 92 db sensitivity, but the load can have low impedance dips and can be reactive (high inductance and/or capacitance). In the latter case, it can significantly change the tonal balance of the speakers and/or cause the tube amp to run out of power, especially in the bass. You should be able to procure an impedance versus frequency curve for the speaker from the manufacturer, or you could ask them if they recommend tube amps. I seriously doubt any type of SET amp would work with these speakers, but perhaps some of the more powerful push-pull amps might.
your krell should be maximizing those dynaudios. just get a nightlight to see a glow. even a big mac with tubes isn't going to do any better.
Unless the speakers have a flat impedance curve no tube amp is going to do them justice for reasons mentioned above by Rlawry.

If you want a refined and liquid solid state sound, consider Pass Labs XA-.5 series amps.
If your speakers do present a difficult load, there is proabably no better all tube amp (hybrids would also work)to deal with dipping impedances the Music Reference RM9 Special Edition which is one of the few amps that actually increases power into 4 ohms (200 watts)compared with 8 ohms (160 watts) and that should be enough power to drive speakers with your sensitivity. However if I did have a difficult speaker load I would proabably look at the Pass XA.5 amps that Tvad recommends.
Increasing power to 200 watts into 4 ohms versus 160 watts into 8 ohms still causes a volume imbalance in the 4 ohm frequencies (they'll have less volume than the higher impedance frequencies). The speakers will sound tipped up with lack of body, IMO.

You need 320 watts into 4 ohms for 8 ohm speakers to produce a balanced sound from top to bottom.

The impedance curve is key. If it's relatively flat, you're in good shape to use a tube amp.
Ultimately your right, difficult impedance loads (not necessarily but jagged, irregualar dips and spikes) really do need SS.
Just a thought you might contact Kevin Hayes at VAC and get his thoughts. I have a Ren 70/70 and it has plenty of power for Dynaudio drivers although the crossovers are custom. I know the speakers efficency is in the high 90's. Kevin's amps have tremendous transformers and really deliver more then there stated output in my experience.

The OP's speakers have an 83dB sensitivity.

The amp's power, or the size of it's transformer is not really the issue. It's the impedance curve of the speakers that matters.

I owned 160wpc VAC amps, which I tried on my Silverline speakers which employ Dynaudio drivers. The Silverlines do not have a flat impedance curve, and the result was an aggressive, tipped-up sound without midrange weight or sufficient low end to balance the highs.
Tvad you must be right because I experience a lush midrange with plenty of balance,weight,and lucidity in both mid and low frequency.
I know an older gentleman who used to own Consequence. He has gone thru many amps, from high power solid state like Bryston 7B-ST to a 70wpc tube amp. His favorite was the medium power tube amp that was made in Canada, but the company has gone belly up and I can't remember the name at this moment.

I used to own Confidence 5 which many believed are the modern iteration of Consequence. I have tried 10+ amps on those and I would not recommend tube with them. The best tube amp I had success with was Sonic Frontiers Power 3, but even then they could not fully bring out the bass.

If you are not dead set on Consequence, I suggest you look for a new speaker that has more resolving power, quicker, more transparent, and easier to drive. As much as I loved the Confidence 5, I have moved on and much happier now.
Your VAC amps are considerably better than were mine, and they use 300B tubes, which have the characteristics you describe. Do you know the impedance specs of your speakers: lowest, highest and nominal? That'd be helpful for anyone reading this thread.
Tvad I don't have the specific info at hand but my speakers are a good match to my VAC 70/70. Just for others,I found this article on the VAC website.
Sound Lab (and all true electrostatic speakers) are a difficult load for the previously mentioned reasons. However, there are tube amps that are very capable of driving them extremely well, Wolcott, Atmosphere and CAT being good examples.
Thanks to all for interesting suggestions and advice.

Rlawry - I have never seen measurements of the Consequence, but the specifications say "Impedance (nominal) 4 ohms, Impedance (20-200hz) 3.6 - 6.7 ohm, Impedance (200-20khz) 2.8 - 4.7 ohm". I am not sure what this means in terms of difficulty or irregular dips. What is clear, is that these speakers thrive with power - the more, the better. (Dynaudio created an inhouse amp, the Arbiter, for developing their speakers, which delivers something like 800 watts and had even more hefty power (I think) than the Krell). Actually, Michael Fremer wrote back "try 2 Krells" and although I didn't quite catch on at first, I do understand what he means (the Musical Fidelity website has info on headroom / power).

Jaybo - the speakers do sound good with the Krell FPB600 in many ways, best with the amp running on higher bias levels, as noticed by Colloms in the Stereophile 97 review already. I measure around 89-94 db 1 meter from the front of the speaker, then they have great dynamics, depth, and an effortless quality to the soundscape where many things can happen at the same time without any congestion. This is where a good s-state/5-way speaker system leaves others in the dust, with complex music especially. So when you have a rock group with orchestra, like Procol Harum "In Concert With The Edmonton Symphony Orchestra", you really get it all.

Not so good for my neighbours though, and a bit more volume than I need late at night. And - there is something with tubes, triode in particular.

Tvad - Pass labs XA-5 noted, will try to find a chance to listen. Likewise, Pubul57 - Music Reference RM9. Wavetrader - thanks, will try Kevin Hayes at VAC, although I note Tvad's point that 160 Vac watts was not enough for his Dynaudio-driven Silverlines. Not so surprising.

Semi - so did your older gentleman who used to own Consequence, give up in the end? That a medium powered tube amp from Canada sounded good is interesting, but I have considered things like Sonic Frontiers Power 3, thinking "not enough".

Changing the speakers is of course a possibility too. I am not dead set on the Consequence. Over the years I've grown to like the Dynaudio sound (e g the Esotar better than most other tweeters). I have read that the Dynaudio Evidence Temptation can sound good with tubes, they are a much easier load, but they are out of my price range. Have anyone compared them to the Consequence? Trouble is, the speakers that I've thought were clearly better, tend to have astronomical price tags, like the amazing Verity Lohengrin (heard at a hifi fair in Horten here in Norway - and even then, I was not sure, on all parameters).

My conclusion, so far, is to keep looking, and try a big tube amp when I get the chance. If nothing works, perhaps the speakers will have to go. I will of course report back to this forum when I have found a good combination.

Rlawry - I mailed Dynaudio, and got the answer that they don't believe in tubes for the Consequence, they mainly adviced me to try the Temptation. Yet their letter did not convince me that they had done much research regarding newer big tube amp designs for the Consequence.

One more point, for other people with good / 'difficult' speakers needing big s-state amps. If you want to chase out transistor sound, look at the system as a whole. I have found that there is a lot to be done to improve the sound, like a dedicated line, good stand, room damping, and a good tube preamp. In my case, upgrading to the all-tube Aesthetix Io was a huge improvement. I've also made a lot of tweaks, mainly to improve damping, including a Bright star sand box and inner bike tire under the record player. In fact I may even have overdamped some things. Somewhat surprisingly, a good sub (Velodyne DD18) has also contributed.
The impedance specs you post above are pretty favorable for a push-pull tube amp running on 4 ohm taps, IMO, since the peaks and dips are relatively flat.

So, I think the recommendations above would be good possibilities...namely VAC and Music Reference.

I have owned a couple of VAC amps including the VAC Phi 110/110, which was stunning. I have heard the VAC 30/30 Signature, which was also magical on a pair of Merlin speakers (although you'd need the extra power of the VAC 70/70).

Have fun!
listen to some manley neo classic 500s or older reference 500s I dont think some of the other suggestions on this thread will drive your speakers adequately
I forgot to say, a Velodyne DD18 with a sand bag on top. I love these tweaks that are cheap and make a clear improvement on the sound...Thanks Tvad, I will.
Which amps mentioned would you not recommend and why? I'm interested to learn the reasoning.
I dont have personal experience with your speakers but I have pretty inefficent speakers myself and have owned the Rm9 (not special edition) and Vac ren 70/70 both great amps but were a little lifless compared to the manleys my experience is that there is no shortcut you need alot of output tubes and massive transformers( I also owned joule grand marquis.) If you are moving from solid state I think the others will leave you a little underwhelmed unless you get a more efficent pair of speakers. But no doubt a tube amp is the way to go!
The Music Reference RM9SE might work as it puts out 200 watts into 4ohms (from the 8 ohm tap on the amp), versus the 65 watts of the RM9 MKII. While it doesn't double power like an SS, it is a tube amp capable of lot's of power into low impedances compared with traditional tube amps. Another tube amp that I think would do the job would be a CAT JL2 - talk about BIG transformers... A tube amp won't do the bass quite like SS does, but I think a worthwhile tradeoff (that you keep to a minimum)with tube amps like the one's mentioned, including the large Manley's.
I used to love Dynaudio sound, from Sonus Faber EA1/Extrema to Dyn C5, but I do believe Esotar 1 is no longer the king it used to be 10 years ago. That's the reason I moved away from Dyn C5, same reason that older gentleman moved away from Consequence. He owns a stereo business and starts importing Eben which has a ribbon tweeter.

Like most inefficient speakers, you need tons of power to have the same dynamic range of more efficient speakers. I am not talking about just playing loud, I am talking about the "jump factor". If you have ever heard a horn system, you will notice how natural the music is, how easily each musical note just flows out without strain, how dynamic contrast is so vivid and relax you don't need to crank up the volume to hear it. so since owning Extrema and C5 for 5+ years total, I decided to go back to more efficient speakers.

I haven't heard the latest Merlin VSM, I did own the VSM SE for a short time. Still using Esotar which you like, they are significantly more efficient and dynamic. if your room size is not huge, VSM MX or whatever version now might work for you both sound and money wise.

I still can't remember the name of that medium power tube amp, but I don't think you should bother trying to find one as I have never seen on goes up for sale on audiogon except the one from the same gentleman who eventually gave up and sold both his amp and Consequence.
If you ar considering changing speakers, I'll second the Merlins (I own the VSM-MXe)which suit my taste to a T; 30 watts is enough for them to be loud and dynamic - The Ars Sonum 30 watt integrated that Bobby at Merlin is importing makes fo a wonderful pairing. But, that is a different strategy all together.
Thank you for all your responses. I have appreciated this thread, you've given me a lot to test out and think about.
O_holter , CAT JL3 mono blocks should do the job nicely for you. I have had allot of amps over the years both solid state and tube and by far these are my favorite. What shocks me is that they out performed any of the solid state amps I have had in the bass region, just so much more realistic sounding.

One other thing is that the CAT's really don't even throw that much heat off, I had a pair of PASS X600.5's and they produce more heat.
I'm also looking for a tube amp for my Dynaudio 52SEs... impedance curve can be found here:

Any thoughts about whether these would be difficult to drive with glass would be appreciated. I'm looking at the Primaluna Dialogue and Melody I880.
Dear respondents,

Dev - thanks for the advice, I will follow up, but not sure if the CAT has enough drive to give the speakers the needed "song and dance" capability. Which my more powerful s-state amp gives even if it isn't tubes.

Robtym - it looks like your 52SE's dip down to 5 ohm in the 20-200 herz region, while my Consequences go down to 3.6 ohm. So a 100-200 watts amp may be enough, in your case (just guessing, i am no expert in this). To my amazement (thinking Dynaudio = difficult load), I recently heard a small Cayin tube amp drive a pair of Dynaudio 140 monitors to great effect, the sound was all over the place, speakers disappearing (a very well-damped room, though).

Since no-one, so far, has come up with a solution based on experience of a good tube amp driving the Dynaudio Consequence speakers, and I like their sound, I am trying various other things (damping, footers, cables).
It's not a question of having enough power to drive the Dynaudios to a proper level, it's a question of frequency balance. Since the Dynaudios dip to 5 ohms in the bass region, and have an 8 ohm nominal rating, I believe it's probable the bass will have less volume than the highs, and therefore the speakers may sounded "tipped up", although it won't be the fault of either the speakers or the amp, but rather the result of a speaker/amp mismatch.

Chapter 15 of Robert Harley's book "The Complete Guide to High End Audio" has a good explanation.
I recently did an in-store audition with the Primaluna Dialogue (38W) on a set of Dyna Focus 120s (4ohm, 86 db, impedance dips below my 52SEs). The Prima is the best amp I’ve heard, for my taste, since I’ve started the upgrade path... which is starting to look more like the opening chapter of an epic journey.

As for SS, I’ve listened to the Exposure 2100, Bel Canto 1000 and Ayre V5-xe, but wasn’t feeling it. The McIntosh MA6900 came close, but didn’t seem to have the presence and life I felt with the Prima... the engaging sense of decay... plus a little aesthetically show-offy for me, to be honest.

I threw a wide range of sounds at the Prima/Dyna combo -- Black Keys, Stereolab, Brad Mehldau, Count Basie – and went louder than I typically do at home (have a 40w Rotel that never goes past 12). Either I didn’t push far enough or don’t have refined enough ears to sense when the sonics are degrading.

It has been suggested to me (by those who know the Prima but have nothing to gain from the sale) that I shouldn’t have problems with my 52SEs as the Prima plays ‘bigger’ than it’s 38W power rating... but I’m still not ready to pull the trigger because of the various concerns I’ve been reading.

I’ll probably go back and push the Prima/Dyna combo a little harder... if anyone can suggest music to help spot deficiencies and/or point out what I should be listening for... I’m all ears.

As I dig deeper... I keep uncovering compelling SS alternatives to glass. The one that seems to stand out is the Red Wine Audio 30.2... so may have to give that a listen as well.

And have also heard good things about Simaudio, Music Fidelity, Van Alstine, Accuphase... all more or less in my budget, available for audition and totally off topic here.

Oh, dear...
If you try your speakers with a tube amp you may want to check out the Speltz zero autoformers. The zeros can double the impedence that your amp will see changing your 4 ohm nominal speakers to 8 ohm.
Tvad, in the case of the Consequence, power does seem to be a main issue, but perhaps your comment was to Robtym (my speakers don't sound tipped up, just 'dead', if they don't get enough power). The Consequences are harder to drive than the monitors discussed here (dipping to 3.6 in the lower frequencies, plus a tweeter and supertweeter arrangement that probably is also demanding for the amp).

Robtym, this sounds much like my experience with the Cayin + Dynaudio 140. I would check it in triode mode. And why listen for problems if you like the sound. On the other hand, I also have noticed that the grass is not always so green on the tube side of the fence (yes the midrange is great and voices lovely, but after awhile...) - and i agree with your comments regarding s-state.

Dmailer, thanks, very interesting. Perhaps it would work in my present system also. I have mailed Speltz and will check this out.

Some good news - 8 Cerapucs arrived today, bought for a reasonable price from a user in Sweden. Compared to my DIY graphite / cones / bike inner tire solutions, they make a definite improvement (so far, under my record player and speakers). Some of what i thought was s-state grunge wasn't (honours to Krell). Probably more to come in this direction.

I am experimenting with grounding and have started a separate thread on this, cf. "Grounding the system" under Amps and preamps.

If you can find Music Reference Rm 9 Mk 1 or 2,it would give you plenty of power and very good sounding.
The Consequence is not that hard a speaker to drive. We've had customers who have had good luck using our MA-2s. That's 220 watts of triode power FWIW.
What is the definition of diffcult speakers? My Focal JMlab Alto Utopias have a rating of 91 db/w/m and have a nominal load of 8 ohms. However, they can go down to 3.2ohms. People told me that my speakers are easy to drive. However, my Melody KT88 monoblocks (50wpc) don't have sufficient bass even using the 4 ohm taps.
Yea, the MA-1's are great, but I hate moving a guy into that many tubes if I don't know him better; as in, can he handle the maintenance and pain-in-the-arse resale.

There are some good comments above. Yea, again, the RM-200 is a great amp and no trouble on resale, but what about all of that biasing? A Defy 7 anyone?! :0)

If I was moving a guy from SS to tubes on an amp and he liked Dynaudio (detail, dynamics, fast and relatively hungry), I'd look at a Berning...It will take hold of Acoustat 2+2's. Its reliable as a tank. Tube rolling is cheap if he wants to and there are plenty of guys out there to talk to him about the amp - knowledgable guys to boot. And, its, um, "nuetral" for a tube amp, so someone moving from SS feels comfortable with it. And on resale, if he wants to later, he barely feels it.

Just an idea...
Good recommendation. As you say, ease of ownership is also an issue moving into tubes, and the Berning is about as plug and play as tube amps can be for someone making the move from SS. Not sure you can find a Berning anymore, I suspect it will be scare on the used market.
Asa, FWIW any Atma-Sphere product that gets updated to the latest level gets warranty reactivation. In addition, the warranty is transferable. This helps with the resale value on amps like the MA-1, which don't tend to hang on audiogon all that long.

Acoustat 2+2s are easily driven with a set of M-60s and a set of ZEROs. They are not a power-hungry speaker.
Hey Ralph, didn't mean to talk down the resale marketability of your OTL's. Hyperbole is a bitch, but then again it is a thread, right? On you MA-1's: I agree, nice amps, great amps, actually. And, yes, they always find a good home, in relatively good time, to the right guy. Hey, maybe it was too much pouring through audiomart newsletters (remember that, Crewe, VA?!), or maybe I've been permanently scared by my Jadis Defy 7 resale experience twenty years ago? Could be...

BTW, I had a friend with the MP-1 and I loved it too, almost bought it; one could swim all day in that luxurious phono. And I like that you are still around, like today, proud of your work.

But, like I said, lots of tubes. It's a psychological fact that, when advising on system evolution, that moving a guy from SS straight into a gazillion tubes may not be the most wise thing to do. I've done it with people asking for help and have seen the faces later. A few more interim steps is sometimes advised. Or maybe not. Like I said, I'd have to know O holter personally to make that decision; mine was a context dependent answer in the middle of a probability analysis...

Basically, I see your MA-1's as a product that is fairly sophisticated; not necessarily in operation, but who ends up there. Please take that as a compliment. With that said, I think that guys who think that they may want to move from 600W SS amps and go SET with a 83db load, might need an interim step. Its the context dependent thing again.

On the 2+2's, we will have to agree to disagree. Granted,I have no experience with the M-60's on the Acoustats, and its been a while since I've heard either on their own, but when I say, take a hold, I don't mean it in a quantitative sense, as in, will it drive the speaker. I was thinking more in the sense, does the speaker speak with its best voice. My comrade had his Acoustats with MA1's and then a Berning and I preferred the MA-1's by a mile(the luxurious part...), so I'm all for the MA-1's with just about anything, including a 83db load. Incidentally, he moved to the Berning because of all of the tubes. But, at the end of the day, I think he might still be tube-rolling the inputs on the Berning looking for that harmonic complexity thing. If you say back, no, the M-60's will drive 2+2's no problemo with dynamic authority and no loss of harmonic nuance throughout the spectrum, then I will defer to you there.

I met you once, Ralph. You won't remember; at a couple of CES's when I was reviewing, and then later at a Chi audiophile club meeting. A while ago now, but what I remember is that you stayed around after the meeting and talked to anyone who wanted to pick your brain. That was nice. More of that in audioland.

Mark Bucksath (Asa)
Hi Mark, the trick to driving Accoustats is being able to deal with the load. A friend of mine had them- wicked low impedance- but we ran them with a set of M-60s and a set of our Z-Music autoformers to deal with the load. They sounded fabulous and could play any reasonable volume- we never ran the system out of power. He had an ARC too; it needed the autoformer as well!

These days you get a set of ZEROs (we don't make the Z-Music anymore) and a set of M-60s will do the job. You would need them even if you had MA-1s; Accoustats are a 'difficult' load, and the ZEROs can be looked at as a great problem solver for things like that. IOW a great way to get a tube amp to drive a problem load.

People often ask if there is a degradation, which is a sort of Red Herring; obviously if the amp can't drive the load 'without', and it does it great 'with', then the answer is 'no, it works great!'
Yep, its the load, impedance-wise on the 2+2's. I should have been clearer. When I talk here about driving a speaker, I tend to talk about impedance/sensitivity together, until I'm absolutely forced to talk about technicals. BTW, I still liked the MA-1s on them. Then again, I'm an SET guy these days, so dynamic compression doesn't bother me as much as most. What are those Dynaudios we are talking about here - 4 ohm load? That sounds familiar in my head.

I've got a second system with 88db (or, 89, I can't remember) sensitive LS3/5A's, but they are 15 ohms, so I can run them quite well with an Air Tight 300B 10W amp. You wouldn't think so, but its works quite well. No head-banging, but its not meant to be that way, can't be.

Anyway, 83db/4ohm speakers I think are going to suck up some serious real estate. To be honest, I think someone you wants those types of speakers should go for a Pass 200 watter and be happy that that's as close as he's going to get to SET, or OTL, mids, spacial rendition and harmonics.

I assume the sans-ZERO MA-1s could do the job, but, then again, he's coming off of 600W of Krell...

Hey, o Holter, what do you say about some big OTL's? Ralph Karsten is here and he's the man...OK, I'm changing my mind...anyone who has Krell on a 83db speaker and wants to go SET MUST be willing to get into the deep end, right?

Ralph, I hope I just helped you with a sale!
I am on holiday and not able to follow this thread so often, so this is just to say, thanks for more advice and suggestions, and also: I use the Aesthetix Io, so I am not exactly new to tubes.
O holter, understood. My apologies. So, then, what about that MA-1?!
They're no longer made, but you might look for a Mesa Baron. Here's one available on eBay.
A couple of years ago I heard two models of Dynaudios large floor standing speakers driven with ease by VTL 450 monos.

On other occasions, Dynaudio Temptation were driven by the superb Atma-Sphere MA-1s.

The Atma-Spheres, VTL and Sim audios Rock solid state amps were a very good match driving Dynaudio speakers.

I would like to add ,I purchased a pair of Dynaudio Special Anniversary 25s in 2004 to use as a second pair of speakers in my system.
I found the Atma-Sphere M60 MK11 monos a thrilling match for the speakers. Even the 30 watt Atma-Sphere amp drove them with no noticeable problems.

For sure I prefer tube amps driving Dynaudio speakers.
If you are going to keep your currant speakers, perhaps try the VTL 750

I have listened to the Temptation on a few occasions and have seriously considered them at one time, a used pair however.

O holter, this may sound crazy for the price difference, however it is for real.

For a fraction of the price the Canadian Grand Veena Reference 3A speakers is a must listen.

Right now I am in the city where the 3As are made. I have listened to them ....Absolutely stunning for the price.

What I heard, I like them better then the Temptations including a few other expensive brands on my shopping list.

Tvads assessment of the issues is a sound one.

Atmasphere takes a very different approach to tube amp design that just might fit the bill. I would investigate this further if I were you.

This is a topic of interest for me as well in that I like what I've heard recently with good modern day tube amps but my Ohm 5's (and Dynaudios) both present a challenging load that I do not believe most tube amps would handle very well.

O Holter, I'd be very interested in hearing about your results if you go the tube route with the Dyns.
A follow up here. I found no dealer in Oslo with a big tube amp, willing to let me try it. Also, dragging 80 kgs is a big burden. Better, then, to listen to others who have tried this, before investing a lot of time and a poor back (prolapsis in 96).
Jaybo, above wrote to the essence that my Krell is already a state of the art case. I think he is right. I find that many things that I thought were due to the "analytical" solid-state perversions of the Krell are in fact other things, that the Krell just communicates. I thought it was "transistor" sound, but changing my system on other parameters make it go away, like using cerapucks under the amp and speakers and ceraballs under the turntable record player. And even, sandbags on speakers and sub.
The Krell is at its best when it plays loud, 90-95 decibels, measured from my listening position (ca 3,5 meters from speakers). This is a bit load for my taste, but at that point, the amp runs at mainly class A, and there is not much to critizise. Especially the synergy with the Io preamp is good. Since the Io is heavily tube-loaded, it tends to correct the trans errors in the krell.

Jaybo is without doubt a "voice of reason" when it comes to giving good equipment its due rather than mining for perceived shortcomings.
I had some experience with the Dynaudio Consequence’s, many years ago, and I still consider selling them cheap one of my biggest audio mistakes. But at that time I did not have a dedicated listening room and as they need a large distance between the speakers and the listener, the best listening position was at the place occupied by a large dinning table…

I heard some of the best sounds in my life with the Consequence’s and the Primare 200 system I am now advertising at Audiogon in a 80 square meter room, but the Krell amplifiers (KSA300s and KAS at that time) and Cello's were the best with these speakers. The Dynaudio Arbiter's and the FM Acoustics were only dreams for me, but a reliable friend who heard them with the Consequence's is still recovering after 15 years.

From my many experiences, including Audio Research Classic 150s, I would not advise using them with tubes, independently of power or electric compatibility. I have now a speaker with a similar behavior in my system – the wonderful Krell LAT1000s. They are a great speaker with the Dartzeel amplifier (200W, current limited) but my VTL 750s even in pentode mode can not control them.

I would advise you on upgrading your FBP600 to 700cx – they are completely different amplifiers, the 700cx is much faster and it should complement the Consequences much better. Also something tells me that the conrad johnson premier 350 – a great LAT1000 driver would be a good match, but is also only a guess.
The big Wolcott amps are reputed to be able to fill your needs.
Microstrip brings more user experience into this thread - experience much in line with my own. When you get these speakers to work, you dont want to part with them. My Krell fpb600 is a good match, although not perfect. I want to thank the contributors in the thread. I will try tube amps when I get the chance.
Borrowed a pair of Quicksilver 2 x 60 watt p-pull monoblocs from a friend. Didn't make it. Not surprising. These are good amps and didn't sound so openly "strained" - but clearly, they didn't grab the speakers in the full way that the s-state does. After two days my family said, why dont you put the old one back. I agreed.