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    M125's Completed.

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    Corona

    Posts : 32
    Join date : 2010-03-11

    M125's Completed.

    Post by Corona on Tue Jan 24, 2012 8:35 pm

    I just finished building my 2 M125's and I've got them working perfect Very Happy

    The instructions were superb and the build was relatively easy and straightforward without any real snags. I'd say that the pair took me a combined 30ish hours to finish with me taking my time and doing high quality work. They biased perfectly without any issues using KT120's, gz37's and 12bh7 driver tubes. At idle they're literally dead silent. I need to put my head right up to the speakers to hear the slightest bit of hum. Already they sound excellent when playing music and they've only been broken in for 2 hours so far.

    Next up: Upgrading everything else in my audio setup. The preamp and speakers are somewhat iffy at best. Pics 'should' work now.

    http://i1113.photobucket.com/albums/k518/EvilRedneck/mj006.jpg
    http://i1113.photobucket.com/albums/k518/EvilRedneck/mj005.jpg
    http://i1113.photobucket.com/albums/k518/EvilRedneck/mj004.jpg







    Last edited by Corona on Wed Jan 25, 2012 8:42 am; edited 1 time in total

    Bob Latino
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: M125's Completed.

    Post by Bob Latino on Wed Jan 25, 2012 9:27 am

    Hi Corona,

    The two amps look great ... You did the right thing in taking your time on the build. Sometimes kit builders get in a rush to hear the result of their work and they rush the build. If you work too long in one session you can get tired and start to make errors.

    Also - I always tell M-125 kit builders to build one amp at a time. Test it, make sure it works properly and then go on to the second amp. If you try to build "both amps at once" you can get confused going back and forth between each amp. You also need a much larger work space to build two amps at once.

    Re: "At idle they're literally dead silent. I need to put my head right up to the speakers to hear the slightest bit of hum." Careful attention was given to wire routing and parts placement in the design of the M-125's. If you do get any hum/noise from these amps the most likely culprit is the front 12AU7/12BH7. This tube is the initial voltage amplifier and any hum/noise in this tube will be carried throughout the rest of the amp. The rear phase splitter/inverter 12AU7/12BH7 usually does not cause hum/noise issues.

    When you have had a chance to listen to the amps a little more let us know how they work out in your music system ?

    Bob

    costerdock

    Posts : 33
    Join date : 2011-07-27

    Re: M125's Completed.

    Post by costerdock on Wed Jan 25, 2012 12:15 pm

    Looks great - I like those rectifiers - one of these days I'm going to splurge and get a pair.

    stewdan

    Posts : 161
    Join date : 2010-03-07
    Age : 78
    Location : Houston Texas

    Re: M125's Completed.

    Post by stewdan on Wed Jan 25, 2012 3:23 pm

    Hi Corona -- looks very good and I am definitely envious!!

    Are the output tubes Tung Sol KT-120's or am I miss-reading the printing on the top of the tubes? The bottoms look like Tung Sol.

    Do your GZ37s provide enough current to run the 4 output tubes at their 125W full power? I thought Bob's info on the M125 was that only the Webers provided enough current for the full output with 4 tubes??

    Thanks in advance, Stew

    Bob Latino
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: M125's Completed.

    Post by Bob Latino on Wed Jan 25, 2012 3:32 pm

    Hi Stew,

    A GZ37 can flow up to 350 milliamps. (See chart at link below) A GZ34 about 250 milliamps. A GZ37 rectifier tube works well in the M-125's and the M-125's won't starve for current with a GZ37 rectifier in there. The tough thing is that GZ37's are expensive tubes. A new one is about $100.

    Tube rectifier characteristics

    Bob

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