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    st-70 balance bias control kit


    Posts : 34
    Join date : 2010-03-06
    Location : Pittsburgh, PA

    st-70 balance bias control kit

    Post by natoe on Wed May 05, 2010 6:22 pm

    I just put one of these items on my clone with the older sds cap board and some Mcshane russian tubes. Just wouldn't come in right the plates were glowing on all tubes put the thing back to stock and we hit a homer. Maybe it is something with that cap board I couldnt get the top side bias set low enough set the fronts to 0 and could only get the tops to .65 volt .40-.50 is the recomended.I will try it on one of my older ones and let eveybody know then.Or on those mark III's

    Posts : 195
    Join date : 2008-11-30

    BBCU Bias Balance Upgrade

    Post by DynakitParts on Thu May 06, 2010 8:45 pm

    Hi Pete,
    Pleasure speaking with you today...

    I actually have a matched quad set of the Russian 6P35-E tubes that I
    purchased before they became known as the McShane-Rusky tubes. Jim is
    a very good source for tubes by the way..

    Our Bias Balance circuit does have some slight effect on the original
    bias range but in all our testing of various EL34 brand tubes and the
    KT77 variants there was no need to tweak the original bias circuit. I
    suspect the operating parameters of the 6P35-E tubes in combination
    with our Bias Balance circuit will require a change of value on one
    of the bias supply resistors. In the stock bias supply, this would be
    one of the 10K resistors but I understand you are using the SDS Cap
    board. I assume the SDS cicuit is similar and the resistor value
    could be changed to support the use of these tubes in your ST-70.

    Over this weekend I will try out my 6P35-E tubes in my ST-70 with the
    BBCU upgrade and let you know what I find.


    Kevin @ Dynakit

    Posts : 34
    Join date : 2010-03-06
    Location : Pittsburgh, PA

    Re: st-70 balance bias control kit

    Post by natoe on Thu May 06, 2010 8:57 pm

    Kevin, the pleasure was all mine. thanks again for your time. I hope you can make some sence of it as I still scratch my head.

    I will be in touch

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    Re: st-70 balance bias control kit

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