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


3 posters

    Blown Fuse on an original Dynaco ST-70 HELP

    avatar
    danagr


    Posts : 2
    Join date : 2016-09-13

    Blown Fuse on an original Dynaco ST-70 HELP Empty Blown Fuse on an original Dynaco ST-70 HELP

    Post by danagr 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


    Posts : 143
    Join date : 2009-12-23
    Location : Valley Stream, NY

    Blown Fuse on an original Dynaco ST-70 HELP Empty Re: Blown Fuse on an original Dynaco ST-70 HELP

    Post by anbitet66 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
    avatar
    Dale Stevens


    Posts : 201
    Join date : 2014-07-06
    Age : 74
    Location : Loris, SC

    Blown Fuse on an original Dynaco ST-70 HELP Empty Re: Blown Fuse on an original Dynaco ST-70 HELP

    Post by Dale Stevens 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

    solderblob likes this post

    avatar
    danagr


    Posts : 2
    Join date : 2016-09-13

    Blown Fuse on an original Dynaco ST-70 HELP Empty Blown Fuse HELP More pictures

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

    Blown Fuse on an original Dynaco ST-70 HELP 20201013
    Blown Fuse on an original Dynaco ST-70 HELP 20201012
    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

    Sponsored content


    Blown Fuse on an original Dynaco ST-70 HELP Empty Re: Blown Fuse on an original Dynaco ST-70 HELP

    Post by Sponsored content


      Current date/time is Thu Mar 28, 2024 6:12 pm