What tube amp for starting out?

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.

Hybrid amps like Counterpoint with solid state output would require less care (biasing, tube life) compared to all- tube amps

OK;
This is my system,
1.ST-70 AMP
2.PAS-3 PREAMP
3.Infinity Primus 360 speakers
I like rock & roll...country..big band..western swing
some classic
I have my doubts about the new EL-34 Mullards
any ideas about a quad

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.

Marco

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".