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

711Smilin, what you see in the power output specifications of the M-60 into different impedance loads (power goes down as impedance goes down and up as impedance goes up) is characteristic of OTLs. (As contrasted to solid state where the reverse happens.) It's one of the reason OTLs traditionally do a good job with electrostatic speakers which can have dramatically rising impedances in the top end.

I don't doubt Trelja's description of his experience with 4-ohm Frieds. But the "conventional wisdom" is not just "urban myth", there's a lot of solid reality to it. Trying to drive 4-ohm speakers with M-60s will be an iffy proposition, and not just due to the reduced power. There will be increased challenges around controlling the woofers effectively due to the impedance mis-match of the M-60 to the 4-ohm speaker load. With certain specific drivers, the matching may work; apparently it does so with Trelja's Freids, but I'd be very hesitant drawing broad conclusions from a single specific example (which I think is an exception). You may get a similar result with your Reimer Tetons, but you may not.

The greater number of output tubes in the MA-1 make it a much more suitable match to a benign 4-ohm impedance curve than the M-60. The increased number of tubes in the MA-1 lowers the output impedance of the amplifier by half (compared to the M-60) and makes for better power transfer into the lower impedance load and better control over the drivers. It's not just a function of the MA-1 having higher rated power output: it's also a function of better controlling the low impedance speaker's driver.

The Zero autoformer can help. But it's not a panacea, and while there are reports from many folks who have been very pleased with the results obtained with the Zeros in their systems, there are also reports from people who not positive about the reulting sound quality.

The best way to get advice about the compatibility of the M-60s with your Reimer Tetons is to call the factory and ask Bill or Ralph: 651-690-2246 If they've had any experience with your speakers, they'll give you a straight answer about compatibility.
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Ralph is back!

Many of you may not be aware of the fact that Ralph Karsten has returned to Atma-sphere, along with his proven track record of product development, customer service, quality, and integrity. The other parties who were briefly running Atma-sphere during Ralph's "departure" in 2004 are no longer affiliated, in any manner, with Atma-sphere. I don't wish to comment further concerning details, since I don't want to see this thread closed. In short, Atma-sphere is back to the same high quality operation for which it has been known for the past 25(?) years!

711smilin, call Atma-sphere (Ralph or Bill) since they will be able to best help you with your decision. And forget about the tax write-off, which only comes into play for an amount OVER the fair market value of a charity item!

Trelja, I would check with Atma-sphere regarding the 12SX7 tube mods. I was lead to believe that this mod was not good for transformer longevity, but I may be mistaken. I was discussing several issues about my amps, and could have misinterpreted or confused information about the 12SX7 mod.

Fatparrot,

Thanks for clarifying that "Ralph is back!" It is good to have him available at A-S once again to talk with.

As to the 12SX7 mod, I haven't heard about this creating any problems. The main considerations for Ralph when I asked about this mod are: (1) increasing cost of the 12SX7 on the vintage tube market; (2) significantly decreasing availability and no "new" production; (3) much better availability of the 6SN7, including great sounding vintage stock (although the vintage is also getting more costly). In short, he's not a fan of this mod and doesn't recommend it for these reasons even though many people report liking the sonic change.
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Rushton may I be honored to say friend, There is a peculiar phenomena when it comes to the supply of old tubes. They come out of every nook and cranny when the demand goes up.
That doesn't address the issue of a low impedance speaker with an OTL sans autoformer. I have heard high powered ones with Avalons on a couple of occasions with excellent results. I have heard Ralph's reputed personal favorite the 60s with the undeniably true Frieds do a great job with the resistive load of the Real thing but have also heard tell of the 30s failing to power a demanding load due a less "benign" impedance load.
Thus get the power and/or make sure your impedance is very firm or will tend to rise before it drops.

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.