Atma-sphere M60 II.3-Any good for 4 ohm speaker?

711smilin, against conventional wisdom, my Atmas have sounded great with a 4 ohm speaker - Frieds. Actually, they are the best amps I have come across for Frieds.

Now, understand that the series crossover (presenting a resitive load) might be the reason, but since your sensitivity is high enough, you might want to give it a shot. The other thing is that a lot of loudspeakers specify a nominal impedance of say, 8 ohms, but the actual curve shows them to be quite demanding. I hear the Reimers are a kind load to an amplifier.

Incidentally, have you bought a pair of Atmas yet? I have an ultra modified pair that I might be able to give you a really good deal on (not yet sure that I was going to sell them). They are MKII.3, plus A LOT of upgrades, such as the 12SX7 (instead of 6SN7 driver - better than any 6SN7), and some other unique things.

711Smilin, your heart is in the right place. You should buy the pair on auction here for the tsunami victims. I offer my personal debt of gratitude to you and Ralph for making this happen.

I actually spoke to Ralph about them this week. They will be built soon, and have the MKII.3 circuit, with the switch to choose Class A or AB. It is his way of giving back, he and I are big believers in kharma. Ralph feels forever endebted to us for taking a stand for him. I feel that we could never pay him back, even if we did what we did a million times, for all of the good the man has done in his life.

I have ZERO idea why anyone would want to run their Atmas in Class AB. Well, yes, I do. They will throw off a lot less heat, as well as using less electricity. But, as the sound will surely take a step down, in my opinion, those interested in Class AB should look elsewhere. Ralph doesn't agree with running them in Class AB, it was a design of the non Ralph regime, and he has told me new designs will forego it in the interest of offering the best sound, at a lower cost (less circuit complexity).

The 12SX7 mod causes no damage to the amp whatsoever. Ralph and I have spoken at length about it, and while he concedes that the tube offers superior sound to any 6SN7, it does not meet his 20 Year Rule, as the tube is no longer in production. One of the reasons Ralph is such a prince is that he wants his customers to be sure that their purchase will still be viable in 20 years.

I think that if prodded, he would do the mod, as it is simple (you just run off of one of the other transformer taps) and easily reversible for anyone who would ever go back (you just switch the wire back to the other tap).

Personally, I disagree with the rationale for not running the 12SX7 - cost. I just bought 8 NOS 12SX7 tubes for $100 last Saturday. I now have more than 2 full sets in reserve. I don't know how long 6SN7 tubes last, but it should be a minimum of 10 years in most tube amps, and probably a lot longer. With the set in my amp, plus two in reserve, I'm probably OK even if I use the amps when I'm 80 years old (I'm 35 now). And, remember, if need be, I could always go back to the 6SN7 after moving just one wire.

Going along with the feelings of everyone I have talked to, including Ralph, that the tube DOES eclipse any 6SN7, tell me where you are going to get a tube that sounds this good for $8 - $30 per tube? Heck, the cheap Sovtek 6SN7s are $10 - $20 each. I know when I was buying good 6SN7 tubes for my last pair of Atmas, I could never find anything for these prices. Yes, they have spiked in price, and it is solely due to Atma Sphere owners such as myself buying them up, but the price is still a fraction of a Sylvania, RCA, or KenRad 6SN7.

Finally, because a tube is no longer in production does not mean it will not go back into production. ElectroHarmonix recently began producing KT90 tubes, which were only produced by Ei in the past and were thought to be soon extinct (NATO destroyed the factory in the 1998 bombing of Yugoslavia). Why did EH start making the tube? Demand, of course. There is money to be made there. If tube amp manufacturers try the 12SX7 and feel it to be superior to the 6SN7 (I hear more and more people talking about the 12SX7) we will start seeing them use it (Denis Had of Cary uses a lot of out of production tubes in his Cary and AES products), and some company like EH, JJ, or Shuguang will begin producing it once again (look at all the tubes that have gone back into production because of Dennis Had). It Economics 101. And, we will be taking audio to a higher plane. Some people focus on problems, I try to live my life by focusing on solutions. It's a glass half empty - glass half full thing.

Fatparrot, the tubes I picked up last week were just about all grey glass RCA 12SX7 tubes. I think that two of them were General Electric as well.

By the way, my favorites so far are a pair of RVC (RCA Canada) grey glass I picked up in the fall. They have the RCA 6SN7 grey glass kind of sound, which is a really fat midbass, lending some welcome (for me) warmth to the sound, in addition to a whole lot of slam. I use them in position V1, which is where I like them best.

It is kind of hard for me to describe their superiority over 6SN7, as the amps that I have that use them came that way. I was never able to listen to them with the 6SN7 tubes. It is a unique pair, and probably one of the finest sets of M60s in existence. They're certainly superior to my former pair, which needed the power supply upgrade as a start.

I will say that the sound of this pair is extremely liquid, relaxed, and natural sounding. Yet, at the same time revealing of astonishing detail, with a good bit more powerf in the bass. This particular pair has a lot of advantages over my former amps - better passive parts (teflon film/foil caps, etc.), a big bump in the power supply, and no negative feedback. There are a few other things with this pair of amps, such as test jacks on each output tube to measure it, the B+ supply has been modified with voltage regulation(I have no idea...) and a "pi filter" has been added to the driver stage power supply. Basically, they were sent in with the mandate to do every possible upgrade known, and that was that.

From other people who are more familiar with the before and after of the 6SN7/12SX7 with their pair of M60s, they are considered a super low distortion tube. I have heard that they take a lot of the best traits of the RCA (big time bass) and the Sylvania (superb midrange and treble) and put them into one tube. Hopefully, someone who has done the surgery can chime in with their opinions here, as I am beginning to drive past my headlights in this post. It's probably also time for Ralph to put me in my place...

Oh, one issue I forgot to address are the chassis of the M60 MKII.3.

There are currently THREE different chassis available.

The old style, with the tubes in the front, transformers in the back, and the squared off transformer covers. This is the classic M60 design.

The "other regime" style, with the transformers running longitudinally down the middle of the amps, with tubes on either side. It looks like the S30 and MA1. I believe Ralph is not a fan of this design and it will be going by the wayside.

The third style is the Rendition, which returns to the classic M60 layout, updated with rounded transformer covers and a stainless steel plate in front of them. It's a takeoff on the original design.

To my eyes, the Rendition looks like the 1940's (streamlined - aerodynamic), whereas the other design looks like 1950s (modernist - contemporary). I like them both. Which do I prefer? I don't know, I keep going back and forth...

While 4 ohm speakers are not kind to the M60s, a lot of people use Reimers with low powered and SET tube amplifiers. I would at least try it. And, regarding the Zeroes, Ralph knows I find they detract from the sound (you lose the AtmaSphere magic). Atma means "soul", and I guess I would just call them Spheres at that point. Still, a lot of people are fans, so you might want to give them a try and see where you stand.