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    Blown Fuse on an original Dynaco ST-70 HELP

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    danagr

    Posts : 2
    Join date : 2016-09-13

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    Post by danagr on Fri Oct 09, 2020 8:21 pm

    I have an original Dynaco ST70 with and updated driver board.

    I guess my problem is I don't even know where to start.  The amp started to develop static on the left channel.  I replace the tubes on that side and it seemed to help but after a couple of hours the static came back.  I put back the original tubes and it was static free for a while and then started back again.  I found if I wiggled the tube the static would go away.  It was working great no static clean sound but I turned it off.  When I turned it back on it had blown a fuse.  I removed half the tubes fuse blown, all the tubes, blown,  changed rectifier blown.  I have the luxury of two dynaco amps and the rectifier and the power tubes work in the other amp.

    I'm thinking a can capacitor is the big silver thing??
    Blown Fuse on an original Dynaco ST-70 HELP 20201010
    anbitet66
    anbitet66

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    Join date : 2009-12-23
    Location : Valley Stream, NY

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    Post by anbitet66 on Fri Oct 09, 2020 8:58 pm

    Hi Danagr,

    If the fuse is blowing out instantly, no, the can capacitor is not the problem - especially with the rectifier removed.  There may be a shorted wire to the power transformer either on the primary side or the secondary side that connects to the amp.  I would check the wiring carefully and test the resistance of the windings of the transformer.  If it is an original Dynaco, there is a good chance that it may be shorted internally.  I see a wire that looks like it is plastic and not cloth covered, but that doesn't mean it is a new transformer.  A little more information is needed.  Can you take a good photo of the underside of the amp including the transformer wiring?  That will help a lot.

    Tony
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    Dale Stevens

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    Age : 71
    Location : Loris, SC

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    Post by Dale Stevens on Sat Oct 10, 2020 10:42 am

    Danagr, yes, send us what Tony suggest. I would first clean and retension all the pins on all the tube sockets. Sometimes, they will loose contact and cause a calamity. Dale

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    danagr

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    Join date : 2016-09-13

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    Post by danagr on Sat Oct 10, 2020 2:46 pm

    Blown Fuse on an original Dynaco ST-70 HELP 20201013
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    Blown Fuse on an original Dynaco ST-70 HELP 20201011

    Looking at one of the sockets in a better light I saw a really fine solder hair that may have been touching across two pins.  Removed it but that wasn't the problem.
    I didn't see any burnt wires or resistors.

    What points would I use to test for shorts?

    Dana

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