Can single ended 211 or 212 amplifiers drive magnepan 20.7?

Also, what do you think about parallel single ended amplifiers? eg 2 or 4 211 tubes per channel? I have heard some people say PSEs lose the magic as their power supply is shared/compromised compared to pure SETs.

@thegreenman The problem with bandwidth in SETs is not the power tube or the number of them used but the output transformer itself. When you put more DC current (used to run the power tubes) through the core of the output transformer, you get a DC magnetic field. This causes the output transformer to saturate, at which point it will make a lot of distortion. 

To prevent that, a saw cut is made in the core which breaks the easiest path for the DC magnetic field, dramatically reducing distortion. The more current you put through the transformer the wider this gap must be. You can see that adding more power tubes is problematic in this regard. 

That saw cut affects the transformer in the bass frequencies. It reduces the inductance of the transformer at those frequencies; the inductance is what is causing the transformer to do its job; were it not there the wire used would be only a few hundred Ohms at best. The power tubes need to see anywhere from 3000 Ohms to 6000 Ohms or more; inductance is what makes that possible so that wire is able to be a much higher impedance for the tubes. So when the saw cut is introduced, at bass frequencies the inductance falls off, causing the power tubes to see a much lower impedance (which is not good for them). They will make a lot more distortion on this account and their service life will be shorter. 

That is why you really don’t want to put bass into an SET amplifier! 

So you can see that simply paralleling more tubes is problematic. The best way to do it is to use multiple output transformers, one for each tube and then parallel their outputs. That way you get lower distortion and wider bandwidth. But you only double the power if only one tube is added.  

But if you have a properly designed PP amplifier you can sidestep a lot of these issues with no downside- literally better in every way and you usually get 4x more power for two power tubes rather than just double. Please note the use of the phrase ’properly designed’ as that is a pretty important caveat. 

But these days class D amps are getting so good that I don’t see the need for a tube power amp at all unless you are really using it see the glow and perhaps enjoy the appearance. You don’t have to sacrifice a smooth midrange or highs, which used to be something only tubes brought to the table. 

I’ve been playing tube amps in my system for 55 years. A few years ago a set of class Ds replaced my triode class A OTL amplifiers in my system (OTL stands for Output TransformerLess; OTL tube amps are arguably the most transparent and widest bandwidth tube amps made) and I’ve not looked back. The class D is just as smooth in the mids and highs and its a bit more revealing. Plus of course no heat and no tubes to replace or worry about. 

@atmasphere wow you really are the master! Thanks so much for your heartfelt advice! Think its the answer tt I dont like, but need to hear! Appreciate it a lot! 

Also, what do you think about parallel single ended amplifiers? eg 2 or 4 211 tubes per channel? I have heard some people say PSEs lose the magic as their power supply is shared/compromised compared to pure SETs.

Thanks! 

i know of those very rare stuff tt prob will, for example NAT audio large tube amps that output 120w class A

@thegreenman The more power you try to get out of an SET design, the more trouble you have with bandwidth. This is true of PushPull tube amps too, but SETs far more so. Generally speaking, if you want hifi bandwidth without profound phase shift, 7 Watts is often the practical upper power limit of an SET. Heap on top of that the fact that only 20-25% of its power is usable before distortion causes the amp to sound 'dynamic' and you can see that if you want to get the most out of SET technology you need a high efficiency speaker in most rooms. 

SETs really don't do well playing bass either. This is because of how the output transformer has to be built to prevent it making a great deal of distortion. So if you want to use an SET in its best light, its a really good idea to prevent bass frequencies from getting into the amplifier at all. 

But you need clean power with Maggies. If you were to bi-amplify, you're better off putting a PushPull tube amp on top rather than an SET. It will be more transparent owing to less distortion and far more musical because of the power requirements. PP tube amps often make about 90-95% usable power.

Class D amps that  use feedback have no problems with Magnaplanars. 

@dseltz thanks so much for your input! :) and really appreciative of such a kind hearted and sweet soul like you offering to lend me your amplifier! :) Unfortunately im not anywhere near New Orleans. But very thankful for nice peeps around like you! ☺️

I have not had experience with Maggies at all lol. At 4 Ohms, the AS Class D would be putting out 200 W, which I would think would be adequate, but those with Maggies can chime in. Following different threads through the years, it seems many Maggie owners answer is always 'you need more power'. 

If you are in my neck of the woods (New Orleans) I could lend you my AS Class D for a trial run.

@dseltz will check them out, thanks! any experience w the class D driving maggies? thanks

@kennyc yeah that would be the best! I guess the only way out is the maggies 30.7 where you can drive the high/mid with SET, and woofers with high powered solid state! but price is abit more, and room size can be a constraint for many. 

@atmasphere thanks for letting me know SETs wont work :( i know of those very rare stuff tt prob will, for example NAT audio large tube amps that output 120w class A, but the price is probably in the stratosphere. but yes I guess you are right in general esp these 2 tubes. Thanks for bringing me back to earth!

@atmasphere hehe you are right! its 7 watt push pull with 4 45 tubes. I mentioned in my original post! hehe normally 45 set is 1.5 watts

To add to @atmasphere post above, there are Class D amps that will drive the Maggies and have a very nice tube like sound. I am referring to the Atmasphere Class D amps. I own a pair (Very reasonably priced even new) and they have almost all of the magic of my 45 SET amp. I am fortunate enough to be driving 106 dB sen. speakers, so about any amp works for my set-up. However, I have an awful room as it is a living room, dining room, kitchen area combined and space is 32' x 28' x 14'. When I am entertaining and need a bit more volume, the Class D substitute VERY nicely. I would not hesitate to recommend a pair. I have not heard them with the Maggies, but believe it would be a great sounding set up.

I occasionally see a pair on sale used, but probably because they sound so good, not very often. 

Never tried. I ran MMGs on an original NAD 3020. It sounded great, but I moved to higher power amps to unlock Maggie’s magic.

my LRS eat up the 350 watts at 4 ohms I have currently.

enjoy the journey

If Maggies could be driven by low watt SET amps, that could be an ideal match for many

@thegreenman An SET based on a type 45 power tube might make about a Watt. Certainly not 7; if your amp really uses 45s and makes 7 Watts, its push-pull not SET. 

But to be clear on your original post, no SET made will drive Maggies. But FWIW there are class D amps now that compare favorably to SETs that will drive Maggies no problem. 

@nogaps actually i have a different experience hence i am asking about this. haha my 25w cary monoblocks have no issues powering my 90db kef reference 5s, and I really love them. I also hahe a dali minuet se that is 86db in my bedroom powered by 7w 45 tube push pull amp. Both have enough volume to satisfy me :) I listen at 80-85 db levels. 

@lcherepkai oic, will go take a looks at your speakers and amplifier! thanks for sharing the experience!

@kennymacc hahaha exactly right! tubes for tweeters and mids, large beefy solid states for the bass! 

No direct experience with the Maggies, but having a sensitivity of 86 dB...I wouldn't think what you're proposing will work, either option.  I once drove a 90dB set of speakers with 60 watts of (KT88) tube power.  Sounded..wonderful..but volume-wise..I could only get to moderately (low-ish) volume.  

By all means pursue the Maggies, but you'll need a tube preamp and some real power.  My current system, due to change completely in a couple months, runs a tube pre into a McCormack DNA1 power amp into 86dB speakers. It totally works. I've enjoyed this system for 10+ years..no complaints.   

I can't answer your direct question, but I did try to use a 45 watt SET (JAS Array 2.1) using 805/300B's to power the ribbon section of a pair of BG Corp Radia 520's  while biamping the woofers with a TEAC AI-3000.  I also did this a pair of VAS Citation II's monoblocks.  The VAS made it work at, up to, moderate levels and sounded delightful in the process.  Rated at the same power, the SET could only muster a diminutive sound.  It simply did not work.  I don't know if the Carys could do any better, but my 45 w SET would not drive the panels to more than a low background listening level.

Short answer..........."NO."  But,  Wouldn't it be loads of fun if the 20.7's could be bi-amped!!!