PX-25 tube amp with Merlin VSM speakers?

I've never heard the Diavolo but FWIW, I've spoke with Joe Fratus (he used to be the man behind Art Audio line in the US) a couple times and I got the impression that the Diavolo was his favorite amp in the lineup.

Dazzlingmd, check out the reviews at 6moons. They have write-ups on the Carissa, Diavolo, Jota and Symphony.

The late John Potis, one of the best reviewers wether on the Internet or print, wrote a perfect review of the Carissa and described it sound and character beautifully. He absolutely nailed it.

Also, I do believe Brf's comment has some value to it. Good luck with your amp search.

Brf nailed it. Quite simply, the Merlin is not suited to most SETs due to their efficiency. Dazzlingmd, your room is only a little smaller than mine, and my speakers are almost 10 db(!) more efficient, yet I find that its nice to have the extra power if I really want to enjoy the speakers. Take that extra 10db away (equivalent to 10x the power) and its just not going to work that well.

If the speaker requires that you are push an SET past about 20% of its full power on peaks, you will not be hearing all the amp has to offer and likely not all the speaker has to offer either. In this case, because the speaker is a medium efficiency, you really need more than just 7-12 watts to really make it play. The bigger you make an SET, the more the bandwidth is degraded by the output transformer.

The advantage of an SET is that it has distortion that linearly decreases to unmeasurable as power is decreased. When you remove distortion, detail is revealed. This is why SETs are known for their great 'inner detail'. However the flip side of the coin is if you want to get everything out of the amp that it really can do, you should not exceed 20% of full power, since above that level the higher ordered harmonics (to which the ear is very sensitive) come into play. That is why the best SET installations often include horn loudspeakers.

You may encounter people that may try to convince you otherwise, but IME (The Merlin is the most popular speaker used with our M-60 amplifiers) you really do need some power to make the speaker sing, even if only a moderate amount. The speaker is very revealing and has surprising bandwidth; what I am saying here is that the performance of the amp won't be realized neither will that of the speaker if you use a low powered SET on it, unless you are in a very small room.

Interestingly, upon a closer review of the specs for my Primaluna Dialogue Premium amp, I'm currently running the Merlins on 12WPC as I use it exclusively in triode mode (which sounds significantly better to my ears than ultralinear), with NOS Siemens RFT EL34 tubes. That gets plenty loud in my small room, has solid bass energy and drive (although I'm not "all about the bass"--more of a treble and mid-range guy, but musical, tight bass is still important). Frankly, my setup sounds good enough right now that a significant part of me wants to just leave things as-is for a while.

But now that I have a dedicated, relatively small room, I have been wanting to test out the magic of the SET sound that many people talk about, just to see if things could be further improved. If I had to point to a flaw in the sound right now, it would be that my system is a little bit too brutally revealing of any flaw in a recording, and accentuates distortion that is sometimes present(for example the notorious distortion at about 5:30 into Stairway to Heaven is quite prominent to the point of distraction, both on the vinyl and the digital files), and overall the sound is ever so slightly forward in the treble range, which is noticeable on some recordings where the treble is a little on the shrill side to begin with.

Atmasphere, I have wanted to try one of your amps in my system for a while as well (and loved what I heard from them at RMAF this year), but people tend to describe the OTL sound as very detailed, revealing and neutral, which is what I have now in spades, in contrast to the typical SET sound which is a little warmer in the middle and slightly softer on top. From those descriptions, trying out an SET amp would in theory be a better fit for what I'm looking for.

In a perfect world, I would demo a bunch of amps in my system of course. The Art Audio Diavolo on that other site is tempting, and claims to have special order upgraded transformers from Art Audio, but the reviews of that amp fairly consistently say it's a little forward in the treble department, which is probably not what I need. In going with just the description of reviewers, the Carissa seems to be a better fit for what I'm looking for. And the 6WPC PX-25 seems to be a higher risk proposition, although now that I know I'm currently only using 12WPC, it's still a little tempting.

Oh, the dilemmas presented by this hobby and all the options. And I know, I know...first world problems...

Dazzlingmd,
I just rechecked and Bobby recommends 17 tube watts minimum for the VSM's. What about a parallel SET that is still single ended but pumps out more watts? They are said to give up little of the SET magic but may give you the power you need. Or how about Decware's Zen Torii? Not a SET but (according to Decware) possessing most SET virtues, sonically.
Or, talk to Bobby. He lives to give advice on stuff like this. :-)