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. 

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. 

@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.