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    12BH7 questions

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    LeGrace

    Posts : 199
    Join date : 2016-08-07
    Location : Ontario, Canada

    12BH7 questions

    Post by LeGrace on Thu Nov 10, 2016 2:04 pm

    Have come across some posts recently extolling this tube as a nicer sounding driver tube versus 12AU7. I also note that the Tube4hifi site indicates "recommended" next to the 12BH7. My M125s currently are populated with RCA 12AU7. Would I notice any difference? Can you mix and match, ie use the 12BH7 in the front and 12AU7 in the rear position? I understand the front position is more sound quality determinant?  Experts please weigh in. Thanks!
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    Peter W.

    Posts : 411
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: 12BH7 questions

    Post by Peter W. on Thu Nov 10, 2016 2:34 pm

    LeGrace wrote:Have come across some posts recently extolling this tube as a nicer sounding driver tube versus 12AU7. I also note that the Tube4hifi site indicates "recommended" next to the 12BH7. My M125s currently are populated with RCA 12AU7. Would I notice any difference? Can you mix and match, ie use the 12BH7 in the front and 12AU7 in the rear position? I understand the front position is more sound quality determinant?  Experts please weigh in. Thanks!

    The 12BH7 draws almost exactly twice as much heater current as a 12AU7. So, if you are running close to the limits of your filament winding, avoid it.

    Gain will be roughly the same-as or slightly better than a 12AU7 due to the higher heater current although the nominal gain is slightly less (16 vs 17 in parallel).

    The BH was originally designed, or so it is reputed, for installation in series filament circuits - and is also reputed to be much more rugged than a 12AU7.

    The short answer is that if your filament winding/transformer is up to it, have-at. They are cheap tubes relative to the more 'popular' devices and so may be worth the time and effort for experimentation.

    NO, ABSOLUTELY NOT if you are within 40% of your filament winding/transformer limits right now.

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    Bob Latino
    Admin

    Posts : 2537
    Join date : 2008-11-26
    Location : Massachusetts

    Re: 12BH7 questions

    Post by Bob Latino on Thu Nov 10, 2016 2:50 pm

    You can use a 12BH7 or a 12AU7 in either position or both positions on your M-125's. The power transformer is "overbuilt" and can handle the extra current draw of a 12BH7. You can also MIX 12AU7 and 12BH7 tubes in the M-125's. If you do, I recommend the 12BH7 in the REAR position and the 12AU7 in the FRONT position. In fact, that is the way I have my own two M-125's set up > A Mullard 12AU7 in the front position on both amps and a GE 12BH7 in the rear position. Photos of my own M-125's at the forum link below ..

    VTA M-125 photos ...

    Bob
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    LeGrace

    Posts : 199
    Join date : 2016-08-07
    Location : Ontario, Canada

    Re: 12BH7 questions

    Post by LeGrace on Thu Nov 10, 2016 3:29 pm

    Perfect, thanks Bob...

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