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MAC Autoformers?

Someone is selling a MAC MA6500 Integrated claiming its superiority over the Ma6600 due to the fact that "it does not have the degrading autoformer design found in the MA6600". That is the first time I've heard a claim that the autoformer was a hindrance to better performance; I thought quite the opposite. What do you MAC Maves think?
pubul57
bifwynne
2,206 posts
 
bdp24, … see my post to Ralph and Roger about the same question.   Theoretically, the 4 ohm taps should work better.  In my case, I subjectively think the 8 ohm taps simply sound better and I do not know why.
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tomic601's avatar
tomic601
13,111 posts
 
i am rebuilding a set of ESL63.... to learn but also listen to....
will start out with a rebuilt MC240 ( which probably has the best transformers available in 1961 !
anyway, my mentor Richard Vandersteen always says run it on the best sounding tap”
but i can see both a Ralph and a Roger amp in my future....
bdp24's avatar
bdp24
10,008 posts
 

Speaking of Richard and Roger, Roger says the idea to install the Capacitor "Forming" function into the MK.2 version of his Music Reference RM-200 amp was a suggestion from Richard. Brooks Berdan sold a lot of RM-9's and RM-200's to owners of Vandersteen 2's and 3's, a great matchup.

For the price of retubing an ARC Reference 150, you can just about buy a used RM-200! The four output tubes run in the RM-200 (producing 100w/ch) last about five times longer than those in the REF 150. How many 150 owners have compared their amp to the RM-200? I’m guessing none. You can buy a used PAIR of RM-200’s for less than a single used Ref 75! There’s one on AudiogoN right now for less than $3k, a ridiculously good deal. I have all the power I need from the one I already own or I’d buy it.

clio09
3,360 posts
 
In addition to Brooks, John Ruttan at Audio Connection used to sell Vandersteen and MR combos and IIRC correctly it was the RM-10 and 2s. Given the new cost of the RM-200 a used one for under $3k is quite a bargain. It should also be noted that the RM-200, unlike most vacuum tube amplifiers which lose power while the speaker load impedance drops, increases output power as the speaker load becomes more challenging. It is stable down to 1 ohm and includes a 1 ohm tap.

While light loading sounds better to me, Roger would also be the first to say use the tap that sounds best to you. There is no reason to not experiment. It's a cheap and easy tweak.
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