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    SCA-35 Questions..

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    boeingpilot

    Posts : 9
    Join date : 2015-06-20

    Re: SCA-35 Questions..

    Post by boeingpilot on Tue Jun 07, 2016 11:53 am

    Ok, another quick SCA-35 question.....

    I gave said amp to my son for graduation. I've noticed after it's been playing for a while I heard a weird sound. Tracked it down to the amp becoming very microphonic, and was causing feed back into the speaker. If I tapped the EL84's, the feed back would go away, but the tubes were VERY microphonic.

    Appears the JJ El84's are quite microphonic. I thinking of replacing these. Any suggestions?


    corndog71

    Posts : 444
    Join date : 2013-03-19
    Location : It can get windy here

    Re: SCA-35 Questions..

    Post by corndog71 on Tue Jun 07, 2016 2:09 pm

    boeingpilot wrote:Ok, another quick SCA-35 question.....

    I gave said amp to my son for graduation.  I've noticed after it's been playing for a while I heard a weird sound.  Tracked it down to the amp becoming very microphonic, and was causing feed back into the speaker.  If I tapped the EL84's, the feed back would go away, but the tubes were VERY microphonic.

    Appears the JJ El84's are quite microphonic.  I thinking of replacing these.  Any suggestions?


    On the cheap side I like Valve Art which are chinese. They'll get the job done although I've heard better ones too. I'm not a fan of JJ tubes due to previous bad experiences although some of their tubes are ok.

    peterh

    Posts : 643
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: SCA-35 Questions..

    Post by peterh on Tue Jun 07, 2016 6:01 pm

    boeingpilot wrote:Ok, another quick SCA-35 question.....

    I gave said amp to my son for graduation.  I've noticed after it's been playing for a while I heard a weird sound.  Tracked it down to the amp becoming very microphonic, and was causing feed back into the speaker.  If I tapped the EL84's, the feed back would go away, but the tubes were VERY microphonic.

    Appears the JJ El84's are quite microphonic.  I thinking of replacing these.  Any suggestions?

    A microphonic tube should be replaced. I have no recollection that jj el84 was susceptible to this, but any tube that has it's internals mounted on mica is sensitive for mechanical shock.
    It can also be problems with the tube sockets or solderings around it , the boards are
    exposed to some heat that might damage them.

    GP49

    Posts : 718
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: SCA-35 Questions..

    Post by GP49 on Tue Jun 07, 2016 9:11 pm

    I'd check for loose sockets and especially for poor solder joints first. Since most SCA-35s were kit-built, I'd always check for workmanship issues in a used one.

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