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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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    st 70 ,new to tubes

    zapped1
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    zapped1


    Posts : 6
    Join date : 2022-10-27
    • Post n°1

    st 70 ,new to tubes Empty st 70 ,new to tubes

    Post by zapped1 Sat Nov 12, 2022 2:43 pm

    Hi all, I have an st70 I'm planning on update/upgrading; PC3a mf resistors, parts; new choke; 80,40,30,20 quad; and bias circuit kit.
    I powered it up running thru a dim bulb tester (don't have a variac). I started adding tubes one section at a time, powered down first of course; the 7199s nice glow on tubes, dim bulb; as the EL34s and the GZ were introduced, the dim bulb burned brightly.
    Being new to tube equipment, I don't want to risk "smoking" the amp or tubes by leaving it powered up long enough to evaluate the ac/dc voltages outlined in Bob's post (st70 quad cap (long post)). I am new to tubes so my knowledge is limited in regards to these amps, so any help/guidance is greatly appreciated Thanks Gary
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    Onlinepeterh
    peterh
    peterh


    Posts : 1869
    Join date : 2012-12-25
    Location : gothenburg, sweden
    • Post n°2

    st 70 ,new to tubes Empty Re: st 70 ,new to tubes

    Post by peterh Sat Nov 12, 2022 3:00 pm

    zapped1 wrote:Hi all, I have an st70 I'm planning on update/upgrading; PC3a mf resistors, parts; new choke; 80,40,30,20 quad; and bias circuit kit.
    I powered it up running thru a dim bulb tester (don't have a variac). I started adding tubes one section at a time, powered down first of course; the 7199s nice glow on tubes, dim bulb; as the EL34s and the GZ were introduced, the dim bulb burned brightly.
    Being new to tube equipment, I don't want to risk "smoking" the amp or tubes by leaving it powered up long enough to evaluate the ac/dc voltages outlined in Bob's post (st70 quad cap (long post)). I am new to tubes so my knowledge is limited in regards to these amps, so any help/guidance is greatly appreciated Thanks Gary  

    Welcome. Don't hesitate to ask !

    But remenber that a tube amp should always have a connected speaker ( or a resistor) on the output(s)
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    zapped1
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    zapped1


    Posts : 6
    Join date : 2022-10-27
    • Post n°3

    st 70 ,new to tubes Empty Re: st 70 ,new to tubes

    Post by zapped1 Sun Nov 13, 2022 1:55 am

    Update: finished installing all parts on the ST70 listed in previous post; PC3A/MF Resistors/Parts, choke, 80 40 30 20 quad, bias circuit kit. new Mullard L34 valves, 7199s (RCA),and GZ34 (Mullard); set the bias, holding steady at 1.56. Right now, listening to Allman Brothers Fillmore (WNEW) through my cheapie "disposable" test speakers...Can't wait to hear the ST with my Altecs!! Tomorrow
    This is the first tube amp for me; I must say that this forum is the best; it was easy to find all the build/trouble shooting info I needed and made the process a lot easier than I thought Thanks

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