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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


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    Permanent Bias Meters

    SoundBound
    SoundBound


    Posts : 13
    Join date : 2011-07-31

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    Post by SoundBound Sun Jul 31, 2011 10:31 pm

    Hello,

    New to the forum, first posting.

    I am currently refurbishing a set of Mark IIIs and about to install the VTA driver board for these lovely puppies. On my wish list, possibly, is the installation of a permanent meter(s) for monitoring the tube bias.

    There are two ways to do this;
    1. A volt meter wired across the bias measurement resistor(s). Scaled 0-2V at best.
    2. A milliameter wired in series with the bias measurement resistor(s). Scaled 0-100 or so mA.

    Question, is this an ok thing to do and which method is preferable to monitor the bias, voltage or current. I know that you can set the bias by either method but will either approach have negative effects on the Mark IIIs ?

    If anyone has any comments in regards, glad to hear them.
    SoundBound
    Bob Latino
    Bob Latino
    Admin


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    Join date : 2008-11-26
    Location : Massachusetts

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    Post by Bob Latino Mon Aug 01, 2011 5:51 am

    Hi,

    Your choice # 1 is the best method. It is basically the same way as bias is now measured on a Mark III except you want a permanent meter to constantly monitor bias.

    Since a VTA driver board on a Mark III has TWO bias measuring points, you will need either two meters for each Mark III or some type of switching device to switch the meter between the two output tubes on a Mark III.

    Bob
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    GP49


    Posts : 792
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

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    Post by GP49 Tue Aug 02, 2011 11:37 am

    #1 is the practical choice, unless you want to replace the 0-100mA meter in series with the cathode circuit, if ever a tube runs away.
    Roy Mottram
    Roy Mottram
    Admin


    Posts : 1840
    Join date : 2008-11-30

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    Post by Roy Mottram Tue Aug 02, 2011 2:01 pm

    I agree, #1 is the way to go, a volt meter won't likely burn out, a ammeter will burn out if the tube runs away.

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