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    Mk4 VTA board.....270k or 220k to bias?

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    Pooch

    Posts : 53
    Join date : 2009-12-01
    Age : 66
    Location : Wa

    Mk4 VTA board.....270k or 220k to bias?

    Post by Pooch on Fri Dec 04, 2009 6:00 pm

    On my Mk 4 VTA instructions I have a diagram and showing 220k ohm to the bias, but in the instructions/ schematic it says 270K? The parts kit I got had 4 220k and I'm sure that's what's supposed to go in there, but curious, why the switch?

    Gord

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    220K resistors instead of 270K

    Post by tubes4hifi on Sat Dec 05, 2009 3:41 am

    Hi Gord,
    I started switching to 220K resistors in that position about a month ago. It's not a critical value, and with some of the crappy tubes on the modern market, it reduces the chance of bias floating away from the correct setting, think of them like pull-down resistors in a semi-conductor circuit, the lower value gives a little more stability.
    Amps using KT88s rather than EL34 usually use 180K or even 150K.
    I'll update the parts list, but I probably marked your parts list when I checked it off showing the change to 220K, even though it's not that way on the schematic.
    Roy www.tubes4hifi.com

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