MAC Autoformers?

unsound
I’ll hazard a guess that Mac chose to use autoformers way back when early transistors weren’t as reliable. They chose to use the autoformers to increase reliability (which way back was part of Mac’s separation from much of the competition) and because it fit in with design parameters that they were already comfortable with. Most speakers of that era were thought to be used with tubes by the end user, that might not have realized the compromises that the autoformers introduced. IMHO, there is no good reason to use autoformers with the rugged transistors that have been available for almost 5 decades since then.

Yes this is well pointed out by unsound, they continued today because of a market niche they made for themselves back then with the "new questionable semiconductors" of the time. They continued with it even though it’s not with today’s semiconductors, and has become the opposite, a compromise rather than an aid.
Or roxy54, a band-aid fix for poorly designed amps that can’t drive certain speakers. In this case your better off with the right amp.

Cheers George

Sure George, whatever you say. This is getting more ridiculous by the minute. It's a shame that listeners all over the world don't listen to you and unsound (good name) and realize that they're wasting their money on this outdated garbage. 

Roxy?
What I'm saying is simple, if an autoformer sounds better with a ss amp into a speaker that amp wasn't a good match for that speaker to start with.
I noticed your avatar and it looks to be one of those amps that would benefit from an autotransformer into speakers it normally shouldn't be mated with. So your happy if it does.
 
You can prove this to your self, there are a number of Zero for sale used some as low as $250 for the pair, put them on a known "good" Solid State amp  that can drive most speakers, and you will put them back up for sale quick as a flash.

Cheers George 

George,

If I did that, the test would be compromised by the fact that the amp used in the test was not designed to be used with autoformers. I really wish that you could have been in my listening room about 9 years ago. I was using at that time a Mac MC 300 and occasionally a Mac MC 2105 which I still own and use periodically. Anyway, I got the audiophile itch, and the darling at the time was the Pass Labs X250.5. I sold my MC300 and bought a perfect one on Audiogon from a member who, coincidentally sold it to buy Mac 501 monos, and later admitted to me that he was so much happier with them than he had ever been with the Pass.
Anyway, that amp was so pretty, and I was expecting this new generation wonder to show the Mac a clean set of heels as the Brits say. I was in for a surprise. I used it with 4 different sets of speakers, and with ALL of them, it sounded thin and transistory. My best audio buddy agreed; and believe me, I wanted to like this amp after having just sold my Mac to get it. I tried extended warm ups, different cables etc. It was, as you said, put up for sale "quick as a flash". 
I use an 8 watt 300b, a 40 watt class A integrated and a Mac 2105. I'm not really what you'd call a Mac fanboy; more of a mature listener who knows what he likes when he hears it, regardless of the technology that was used to achieve that sound. My point to you is less about defending McIntosh and their circuit topology, and more about judging gear, any gear, on the merits of its performance, and not how "correct " it is the estimation of electrical engineers. I've been through quite a few amps, more than some and surely less than others, but if the Macs weren't better than most of what I've owned, I wouldn't still be using one. 

If I did that, the test would be compromised by the fact that the amp used in the test was not designed to be used with autoformers.

Wrong, your grasping for straws!

The autoformer is just as suited to a good amp compared to one that is compromised.

And if your happy with it that’s fine.

BTW shoulda kept the  Pass Labs X250.5

Cheers George