Your price range would help. Having said that Conrad-Johnson is a great place to start. I've owned a number of their amps and have always been satisfied. There are many other companies out there and depending on $'s other choices could be better. You could probably get something used on the 'Gon and try it. If that does not work sell it for about the same and try something else.
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Depending on your budget I would recommend a McIntosh MC275IV as your #1 value Excellent sound, built like a tank and great resale value over the years, they can be bought used at good prices.
Cary V12, there are plenty around used. Conrad Johnson Premeier 11a, MV60SE are also great choices.
Pleae stay away from VTL-hard to service and very rude people at the factory
I would second a used conrad-johnson MV-50, 52 or 55. It uses the same large tubes as your Dyna (6CA7/EL34/KT77)and puts out just a bit more power. They are very reliable and will be a big step up clarity, detail and dynamics. Used prices are in the $750.00 to $1200.00 range depending on model and condition.
Again get it right the first time,MC275IV,I have one and it is one great amp.It is auto bias so you never have to worry about biasing after new tubes if you get into tube rolling.If you stick to stock tubes they are rated for 3,000 plus hours.You can get a low hours used one on Agon for around $2700.00.
If I had any component that was "dead in the midrange" it would not be in my system very long. Boy, if you don't have the midrange right, then it will be very easy to find an amp that does better. I heard a friend's modified Dynaco many, many years ago and was very impressed with it, but couldn't comment beyond that. Have you tried rolling the tubes with various different brands? Could you have some bad tubes in there that are holding it back?
As far as a replacement, as Tvad points out, you might want to post the speakers you are using in order to get more informed input on the subject. Are you intending on keeping the other Dynaco components? The price of the "most realism possible" can be very high indeed. Also, what you find to be "realistic" may be different from what another person finds that way. You should probably also consider stating a budget, or you will get suggestions from a few hundred dollars to tens of thousands of dollars.
Groundhog, like Tvad has said, we need to know what kind of speakers you're driving. Better yet, give us your entire rig and the music you love most. Then we can give you some tips on what may help you out. Realistic, but dead in the mid range? The core, the gestalt of realism is in the midrange. This is where most of your music is. Maybe you don't require a new amp. This could get to be an expensive answer to your question or just the reverse.
I would address those speakers, and leave the other components for now. Replace the speakers with a pair of used Klipsch Forte II's or Chorus II's and I'll bet you'll be cooking with gas for the kind of music you like. Those speakers do very well with tubes. Before taking that step I'd really make sure that there wasn't something wrong with the gear you already have. I've not heard anything with the "new" Mullard EL-34, but the NOS ones certainly are of the very best out there. Does your amp require manual biasing, and if so, have you checked the bias? Have you checked all the tubes with a tube tester to see if they're good? Are any more than a couple of years old? I have no idea who did your upgrade, but the Dynaco's are certainly decent amps that wouldn't fall that short in the midrange as you describe. What about the preamp tubes - have you checked those and could any be getting long in the tooth? Also, what is your source component...you mentioned a Dynaco Tuner, do you also listen to CD and or LP? Do all sources sound flat in the midrange? The success of a system is a matter of synergy between all the components as well as their links, including the room they're making music in. The weakest will cause the rest to suffer. It could be your room too, but first check on the components and making sure everything is as it should be.
Excellent suggestions from Marco. All bases are covered.
I will only add that the Infinity Primus 360 have an impedance dip to 4
ohms in the lower midrange and upper treble (per John Atkinson's measurements in Stereophile), so if you decide to keep them, you should look for an amplifier that can handle that load. At the very least, it should double it's wattage into 4 ohms from its 8 ohm rating, otherwise you will hear a recess in these regions. Frankly, this might explain what you're presently hearing with the Dynaco amp when you say the sound is "dead in the midrange".
Good research Grant. Yes, with a significant dip in the lower midrange you might need a bit more muscle than your Dynaco can muster. I would sooner try more compatible speakers rather than sell off the Dynaco gear. But I don't know what of your system you may be more attached to (nor why). On the other hand, for most of the music you like to listen to, I would have suggested you consider SS or Hybrid amplifier, rather than tubes. It may not have the same warmth and dimension that tubes have, but it will have dynamics, speed and impact that your Dynaco won't ever be able to deliver. This is what I was hinting at when I said your idea of "realism" may be different from other's. Depending on what you regard most highly in the way a system presents the music, you may want to pursue a different direction. In my experience, no single approach does it all. There are always some compromises, especially so at this level of components and investment, and even at higher levels. That's not to say you shouldn't be able to have a great sounding system with some of the gear you already have. Weigh your priorities, find the weak links, and proceed.
Hey Grant, you and I should approach NPR and start a new radio program Stereo-Talk. Do you have strong regional accent? I can put on my Brooklyn accent - I lost it at age 15, when we moved out of there, but I can put it on when I need to.
At the very least, it should double it's wattage into 4 ohms from its 8 ohm rating, otherwise you will hear a recess in these regions. Frankly, this might explain what you're presently hearing with the Dynaco amp when you say the sound is "dead in the midrange".
could the 4ohm output taps be used then?
4 ohm taps would be a requisite with the Infinity loudspeakers, but this
is not a guarantee that the Dynaco doubles power into 4 ohms. The
Dynaco can probably be adjusted so the taps are 4 ohms, if they don't
already allow for this.
Another option would be trying Speltz Zeroformers that double, triple or
quadruple impedance...effectively doubling the Infinity's 4 ohm
impedance to 8 ohms, but they also would double the 8 ohm impedance
to 16 ohms, so the curve wouldn't change even though the load would
become easier. I've never tried them myself, so I have no idea how they'd
work, but theroetically they are an option for this scenario.
The advantage of an amp that doubles its wattage into 4 ohms versus 8
ohms is that it flattens out the speaker's response curve. Therefore
certain frequencies aren't emphasized over others, as would be the case
with the Inifinity's dip in the lower midrange and upper treble
Personally, I'd rather have a good speaker/amplifier match without
having to add fixes in between.