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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 problem - 2 of 3 preamp tubes won't glow

    slowhandsonfire
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    slowhandsonfire


    Posts : 1
    Join date : 2014-03-04
    • Post n°1

    st-70 problem - 2 of 3 preamp tubes won't glow Empty st-70 problem - 2 of 3 preamp tubes won't glow

    Post by slowhandsonfire Tue Mar 04, 2014 8:32 pm

    I recently moved into another house, and somehow in the process of transporting my ST-70 I damaged something. When I fire up the amp, I get no sound. Only the left preamp tube will glow; the center and right ones stay cold. I know it's not a tube issue because I tried all 3 tubes in every preamp tube slot and the only the left one got hot every time.

    Any ideas what could be wrong?
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    Bob Latino
    Bob Latino
    Bob Latino
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    Posts : 3263
    Join date : 2008-11-26
    Location : Massachusetts
    • Post n°2

    st-70 problem - 2 of 3 preamp tubes won't glow Empty Re: st-70 problem - 2 of 3 preamp tubes won't glow

    Post by Bob Latino Tue Mar 04, 2014 8:37 pm

    One or both of the two wires that go from pins 2 and 7 on V6 to the driver board have become loose on either the driver board FIL eyelets OR pins 2 and 7 on V6. Even if they look like they are still connected > resolder those connections ..

    If you also get no sound on the left channel, it is possible that the rectifier tube got shook around during your move and the rectifier tube is now bad. I have said this before on the forum here > Just because a rectifier tube lights up, it does not mean that the rectifier tube is GOOD. If you get no DC voltage from pin 8 of the rectifier tube socket to chassis ground, your rectifier is bad.

    Bob
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