sweet, euphonic, reasonably powerful tube amp?

Circuit design is an obvious variant but apples to apples I have found that the EL-34's have a seemingly more inherent midrange richness than the 6550's or even KT-88's My experience is based on my last tubed monos, the VTL MB-125's which are 4 x EL-34's per channel and can do tetrode or [1/2 power] triode. They provide much of what you're seeking in tetrode but almost all you're looking for in triode. I can also second the recommendation for the older MV series CJ's, perhaps an MV-125 IF you can find one (I've had my eye out for one for awhile) or an MV-100. I went to CJ from the VTL's with Premier 12's right now which are using 6550's. Sound went from velvet to silk in the midrange (rich and creamy to less fat but more "zest"), bottom went from ballsy, fast and strong to even faster, a bit leaner, somewhat more defined, and the top end went from ever so slightly rolled off (but didn't miss it), relaxed and natural to considerably faster, more detailed and extended but with no hints of harshness or bite. Each sound is a new acquired preference but it sounds like the EL-34's meet your description better. VTL also makes an EL-34 based bigger pair of monos.. I think they're MB-250's or so ?? Correct me if I'm wrong. I know they made MB-225's that were strictly triode and used 6550's but they also had a tetrode/triode switchable one with the EL-34's too I think. Might be worth a listen.I've also heard great things about the Dodd 120 monos (again, EL-34 based). Good luck.

For fear of making even more generalities here we all have our deserved experience based opinions but lets dabble a bit more with [hopefully] more of these and not our pre-conceived notions. As stated above, circuit design can significantly extract uncharacteristic impressions from tube types you'd never suspect (both positively and negatively), so I find it prudent to reiterate the minimal use of the terms "good or bad" when it comes to the general description of a certain tube-type's sound. With that said, personally I haven't found an EL-34 based tube amp that I didn't find appealing in its overall musical delivery They are generally characterized by a "lusher" sounding midrange and as such will typically deliver some extraordinary vocals and many stringed instruments also sound particularly warm and inviting. It's frequency extremes are sometimes less impressive because the top end MAY come across as a bit rolled off and the bottom may not be as extended as others. This is only IMHO, as there are many others who are far more experienced in specific tube rolling and swapping brands of NOS, etc, who can fill you in better than I. As for the VTL house sound, I believe it is considered a good natural and lifelike midrange, powerful, punchy lows, and "pleasant" but not necessarily extended highs.... and this has been my personal experiences with them. The 6550 based amps will probably be a little more extended at both extremes and a bit less lush sounding in the mids.. I've grown accustomed to this sound (especially with the EL-34 based amp) and as I said before, am "re-adjusting" to the CJ sound (using the 6550's). Triode mode will differ from a 6550 (brighter) to an EL-34 (more romantic) also, and this is what I was basing my first response to your inquiry on. There are plenty of other ways to "persuade" your end result sound such as speaker cables and I/C's as well as powercords.... each area is another can of worms to sift through... and that would be another thread too. Good luck.

You can guess my vote... my VTL MB-125's stayed in my system longer than any single component ever did for very good reason (about 7 years). The tetrode mode could kick butt all over the place and the triode mode ( mostly late night listening) was the unifying thread between a good cabernet, candle light, and all that romantic kind of stuff.... what it did for intimate vocals and the fireplace-on-a-cold-winter-night thing was incredible. The Premier 11 will be very very close to my changeover to the Premier 12's was...as per above; I suspect you'll like it more than your ARC based on what you've been saying and it may be a good step in the right direction without going too far right away. Good luck with it and keep us informed.