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    intermittent hiss problem.

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    baddog1946

    Posts : 304
    Join date : 2010-02-03
    Location : Costa Rica

    intermittent hiss problem.

    Post by baddog1946 on Sun Feb 17, 2013 5:03 pm

    A couple of days ago my ST-120 started to make a low level hiss on an intermittent basis. It disappears irregularly and there is no noise whatsoever when its gone, even with the volume jacked up.
    It seems completely normal but in a minute or so it begins again and cuts in and out. Before I pull it apart to check it out do any members or Bob have some suggestions on where to look first or some tests to eliminate the most common issues and a drawn out trial and error process? Any members help would be appreciated.
    Baddog

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: intermittent hiss problem.

    Post by Bob Latino on Sun Feb 17, 2013 5:22 pm

    Baddog,

    As a first try to remedy the issue ... Replace the CENTER driver tube with another tube and see if the hiss goes away . ...

    Also you didn't mention whether the hiss was on one or both channels ?

    Bob

    baddog1946

    Posts : 304
    Join date : 2010-02-03
    Location : Costa Rica

    Re: intermittent hiss problem.

    Post by baddog1946 on Sun Feb 17, 2013 5:23 pm

    Both channels.

    baddog1946

    Posts : 304
    Join date : 2010-02-03
    Location : Costa Rica

    Re: intermittent hiss problem.

    Post by baddog1946 on Sun Feb 17, 2013 5:32 pm

    Ok I swapped the center tube and it made no difference.
    Amp came on with the hiss steady but after a minute or so it became intermittent again.
    I am using 3 Mullard 4024 tubes in there which all test fine on my tube tester.

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: intermittent hiss problem.

    Post by Bob Latino on Sun Feb 17, 2013 7:44 pm

    Hi George,

    Your amp is about 3 years old .. It could also be a dirty tube socket on the driver board. Try cleaning the pins with some WD-40 and reinserting the tube a couple of times.

    Do a full voltage check on the amp as outlined in the manual. Listen to the amp as you make the voltage check. When the amp makes the hiss noise, see if possibly one of the voltage check points changes its voltage slightly during the hiss.

    Bob

    baddog1946

    Posts : 304
    Join date : 2010-02-03
    Location : Costa Rica

    Re: intermittent hiss problem.

    Post by baddog1946 on Sun Feb 17, 2013 8:13 pm

    roger that thanks!

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