Old tube amp?

Go for the Dynaco ST-70, and you can convert to monoblocks later(if the fancy strikes you). Then again: You could start with Mark II, III or IVs to begin with. WHATEVER you do: Buy stuff that hasn't already been modded. There are a bunch of audio butchers out there!! You may find yourself in the position of a doctor trying to undo an abortion. Here are a few sites that offer excellent upgrades: (http://www.curcioaudio.com/) (http://www.triodeel.com/dynaco.html) (http://store.triodestore.com/dynacoupgrades.html)If you don't want to get that radical with the upgrades right away: Just beef up the power supply, replace all the caps and resistors in the signal path, the power cord, input RCAs and output terminals(not hard, or expensive at all), and enjoy the music like that. Dynaco parts, data and knowledgable modders are always available,(and always will be)because there are so many and they are so popular. There are even brand new kits out there that enable you to build one yourself. Mo stuff: (http://www.zeemash.com/cgi-bin/search.py?keyword=Dynaco%20St%2070)

The Dynaco ST 70 would be a very good start. But a stock ST 70 or one with stock 7199's won't give you as much detail as boards from Van Alstine, Curcioaudio, Triode, Mapletree (? out of canada)Kennedy, Sound Valves and GSI.
You should also have a newer power transformer which handles voltages better and offers tighter bass.
I'm using a Sound Valves input board on my ST 70 and all my updates and mods were done by Tom Tutay of Transition Audio Design. I have had my amp for over 10 years and I have retubed it only about 4 times. I have put it up against many and I mean many other amps and the ST 70 still continues to impress me. You do have to stay within your power envelope on most speakers but I have never run out of steam. I'm driving a pair of Magnepan MG12's in a 13 x 14 foot room with a 14' ceiling. I have an excellent soundstage, and rhythym and pacing with that combo. I have been searching for most of the last 6 months trying to find an amp that sounds better and I have yet to do it. I have tried several solid state designs int he $2000 range and while they sound good they didn't make me want to shelf my ST 70.

There are many modifiers out there. If you find someone whose circuit you may have interest in contact them and see if someone in your area has one that you can listen to.
My favoites are Sound Valves input board with Tom Tutay mods and updates to my ST 70 then GSI and Van Alstine. The GSI is very hard to find. If you need more power look at Quicksilver monoblocks or GLA a 40 watt stereo amp. One of these were on this forum a week or two ago. These would proably be a very good match with your Merlins.
If you can find a Berning EA 230 or 2100 they would be excellent. But they are very hard to find and prices are rising each time I see one. I'm speaking of being Musical period......
And last each of the amps I mentioned have their very own sound signatures. The Merlins deserve more than classic tube sound. You need refinement. The refinement should not come at your expense by parts swappers but with a qualified individual that can make that amp sing and be reliable at the same time. If you have a ST 70 and want it modified call Tom Tutay at 850-244-3041 CT. I'm sure he will give you an amp that will satisfy your Merlins. Make sure the chrome on your ST 70 is excellent if you decide to go that route. If it is you will get a higher resale value for it. Rust pits will de-value your ST 70.
One last thing You may want to check out the Onix/Melody EL 34 based amp. The 6L6 version was nice. I hear the EL 34 version is even better. Priced under a grand too.

The general consensus is a Dynaco but another option is the Scott 299 or 340.

IMHO, EL-34 based amps will sound decidedly different from say KT-88
based amps on your Merlins. I would guess that your personal preference will
probably steer you firmly one way or the other, but it may just get you
thinking. In any event, I'd try to a-b any KT-88 vs any EL-34 prior to buying.
One advantage of the Prima Luna amps is that they allow you to roll from one
to the other. I own a pair of these amps for use wiith VSMs (and a few other
speakers) and the character of the VSMs definetly shifts with the tube roll.

Good Luck,

Marty

I am also a big fan of the Dyna ST70, but I prefer it stock. It definately has its flaws, and many of the popular mods improve some of these flaws quite a bit. But none of them really transform it into a super-amplifier, and the original design is a masterful work of simplicity and careful compromise. I recommend that you give the original circuit a chance first, so you then have a good understanding of what the modifications are doing.

And while it may push your budget a bit, you should look for McIntoshes as well. You might find an MC240 that sounds great but is cosmetically flawed for pretty close to your price range. They are much more stable, consistent, and reliable than Dynacos, they use extremely common power tubes (6L6s), and they operate the circuit in such a manner that the tubes last much longer as well. Oh and the sonic performance is a HUGE step over a Dyna.