The Dynaco Tube Audio Forum

Would you like to react to this message? Create an account in a few clicks or log in to continue.
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


    ST-70 Tube Rectifier Duplication

    avatar
    franksr

    Posts : 1
    Join date : 2020-08-22

    ST-70 Tube Rectifier Duplication Empty ST-70 Tube Rectifier Duplication

    Post by franksr on Sat Aug 22, 2020 10:41 pm

    Hello all. I’m new to the forum and am hoping someone can help answer a couple of questions. Many years ago I rebuilt my ST-70 using a Purist Audio Design input board modification. It uses 12AX7 tubes instead of the original 7199’s. I have no problem with the board and like it very much. I don’t remember much about the modification but I also ended up using two 5AR4’s instead of one. The amp has performed flawlessly for decades. My first question is does the second rectifier offer any advantage or is it possibly causing harm? I’m running the EL34’s in triode mode. I don’t remember what I did to wire it for triode mode. Seems like I added a jumper to some of the tube pins but I’m not sure. I would like to try the amp in ultralinear mode and may add a switch to allow me to switch back and forth. Can someone tell me if I am recalling this correctly, and if so, how to return the amp to ultralinear mode? Thank you very much for your attention.
    peterh
    peterh

    Posts : 1403
    Join date : 2012-12-25
    Location : gothenburg, sweden

    ST-70 Tube Rectifier Duplication Empty Re: ST-70 Tube Rectifier Duplication

    Post by peterh on Sun Aug 23, 2020 2:27 am

    franksr wrote:Hello all.  I’m new to the forum and am hoping someone can help answer a couple of questions.  Many years ago I rebuilt my ST-70 using a Purist Audio Design input board modification.  It uses 12AX7 tubes instead of the original 7199’s.  I have no problem with the board and like it very much.  I don’t remember much about the modification but I also ended up using two 5AR4’s instead of one.  The amp has performed flawlessly for decades.  My first question is does the second rectifier offer any advantage or is it possibly causing harm?  I’m running the EL34’s in triode mode.  I don’t remember what I did to wire it for triode mode.  Seems like I added a jumper to some of the tube pins but I’m not sure.  I would like to try the amp in ultralinear mode and may add a switch to allow me to switch back and forth.  Can someone tell me if I am recalling this correctly, and if so, how to return the amp to ultralinear mode?  Thank you very much for your attention.
    Unfortunately the batterys in my crystal ball has gone out. I need schematics to answer the question.

      Current date/time is Thu Sep 24, 2020 1:35 pm