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    ST70......some symptoms

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    Greg_M

    Posts : 40
    Join date : 2010-09-18
    Location : Poulsbo, WA

    ST70......some symptoms

    Post by Greg_M on Fri Sep 24, 2010 10:42 am

    Got the ST70 working and it's playing fine. Probably needs new tubes. I have a new pair of EL34s but haven't put them in since the old ones are working.

    I've put in new caps, ceramic sockets, quad cap and rewired most of it.

    When I power it up it makes a hum noise a few times, as though you were touching the center conductor of the audio input plug with your finger. It does this 3 or 4 times for a fraction of a second, then it goes away and never does it again.

    The choke looks like it has experienced some heat at some point in it's life as the chassis around it's mounting position is brownish. It still measures the correct amount of ohms. What are the symptoms of a bad choke?


    Greg_M

    Posts : 40
    Join date : 2010-09-18
    Location : Poulsbo, WA

    Re: ST70......some symptoms

    Post by Greg_M on Fri Sep 24, 2010 1:28 pm

    Update

    This morning I turned it on and watched carefully and could barely see a very faint blue light (I thought my eyes were tricking me at first) that coincided with the momentary hum noise. So I am fairly certain it is that one tube going out.



    Greg_M

    Posts : 40
    Join date : 2010-09-18
    Location : Poulsbo, WA

    Re: ST70......some symptoms

    Post by Greg_M on Mon Sep 27, 2010 8:28 pm

    Fixed!

    It was one of the output tubes on the left side. Either the Dynaco or the Realistic Lifetime (made in Germany)

    Replaced them with Electro Harmonics and it sure does sound good


    Happy Days

    Sal

    Posts : 221
    Join date : 2009-02-05
    Location : Central New Jersey Dynaco-ST70.com

    Re: ST70......some symptoms

    Post by Sal on Thu Sep 30, 2010 11:27 pm

    Nice job finding out your problem was a bad tube.

    Sal

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