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    ST120 rectifier question

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    wgallupe

    Posts : 85
    Join date : 2014-05-18
    Age : 62
    Location : Central Mass.

    ST120 rectifier question

    Post by wgallupe on Tue Jul 21, 2015 7:36 am

    Hi All,

    Since my audiophile buddy and his wife are visiting for the weekend, I thought I would bring my Magnepan MMGs up from the basement to see how they sound with the SP13/ST120 combo. The ST120 powers my GR Research OB5s very well. They are rated at 91dB at an average of 6 ohms and minimum resistance of 4 ohms. The MMGs are rated at 85dB and a constant 4 ohms.

    Will the rectifier, currently a Mullard GZ37, have to work harder to drive the MMGs? (I am also running Tungsol KT120 power tubes). I should add that the speakers are running off the 4 ohm transformer taps.

    Should I put a Webber in for the MMGs?

    Thanks in advance.

    Wayne

    Bob Latino
    Admin

    Posts : 2414
    Join date : 2008-11-26
    Location : Massachusetts

    Re: ST120 rectifier question

    Post by Bob Latino on Tue Jul 21, 2015 7:50 am

    Hi Wayne,

    I would just keep the Mullard GZ37 in the amp .... Although the Weber rectifiers can flow more current than the GZ37, the amp will play fine even at high volume levels just as good as the Mullard GZ37 (or the Mullard GZ33). The GZ37 will work a little harder but these tubes are very durable and can take the extra stress in stride ...

    Bob

    wgallupe

    Posts : 85
    Join date : 2014-05-18
    Age : 62
    Location : Central Mass.

    Re: ST120 rectifier question

    Post by wgallupe on Tue Jul 21, 2015 8:44 am

    Thanks for the quick reply Bob. I'll post comments after the 'test'.

    wgallupe

    Posts : 85
    Join date : 2014-05-18
    Age : 62
    Location : Central Mass.

    Re: ST120 rectifier question

    Post by wgallupe on Wed Aug 19, 2015 2:48 pm

    Following up on my previous comments, my buddy and I did indeed drag the Magnepan MMG speakers up from the basement system and set them up with the SP13/ST120 combo. We played some favorites: Dire Straits Brothers in Arms, Supertramp Crime of the Century, Heart Dreamboat Annie, Norah Jones Come Away with Me.

    The good news is (there’s no bad news) that the ST120 had no problem at all driving the MMGs. Compared to the GR Research OB-5 speakers, the MMGs sounded darker and the bass was a fair amount ‘fatter’. Sort of like the difference in sound between running the amp in triode mode instead of pentode mode with exaggerated results. There’s no doubt that I preferred the OB-5s in this brief, uncontrolled comparison. In hindsight, I should have tried swapping out the NOS Mullard and Amperex driver tubes in the ST120 with RCA clear tops that I have on hand. I’ll bet the clear tops with their leaner/tighter sound would have closed the gap a bit.

    Oh yah, the GZ37 did not seem to care which speakers were hooked up!

    sKiZo

    Posts : 1312
    Join date : 2013-04-01
    Location : Michigan USA

    Re: ST120 rectifier question

    Post by sKiZo on Wed Aug 19, 2015 3:25 pm

    My big box McIntosh XR16's are rated at 89db and the ST120 will literally rock the room. That's WITH expansion and bass synth which will work any amp harder.

    And that's with a GZ37 AND driving a quad of KT120's ...



    I've still got a WZ68 copper cap for backup ... along with another GZ37. Hard as those are to come by, it seemed wise to get a spare.

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