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    flashing pre tubes, and complete failing of same.

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    scottlowe

    Posts : 38
    Join date : 2014-04-05

    flashing pre tubes, and complete failing of same.

    Post by scottlowe on Wed Jul 23, 2014 3:38 pm

    Hi I am back with another question. I have been trying different pre amp tubes [12AU7's] and yesterday tried some Questionable tubes and one of them flashed when first turned on then ran ok, another flashed and blew a fuse. I replaced all the pre tubes with some clear tops that I have been using [fuse too] and all is good again . My Question is if a tube shorts out can that harm an amplifier?[ VTA ST-120 ]The amp is running flawless again and the new kt-120's [from Jim McShane] are very stable and sound SUPERB.thanx Scott

    Elrick

    Posts : 71
    Join date : 2012-09-02
    Location : Bellingham WA

    Re: flashing pre tubes, and complete failing of same.

    Post by Elrick on Wed Jul 23, 2014 9:29 pm

    12AU7's probably not.

    nmchiefsfan

    Posts : 33
    Join date : 2012-03-21

    Re: flashing pre tubes, and complete failing of same.

    Post by nmchiefsfan on Wed Jul 23, 2014 10:57 pm

    Some of the small signal tubes (mullards) will flash when they powered on after being cool.  It is known as the "mullard flash"   As for the fuse blowing, perhaps that was actually a bad tube.  Here is a video of the mullard flash from youtube http://www.youtube.com/watch?v=uYXjAOW61-g

    Gregg R.

    Posts : 80
    Join date : 2014-02-20
    Age : 71
    Location : Land of 11,842 Lakes

    Re: flashing pre tubes, and complete failing of same.

    Post by Gregg R. on Wed Jul 23, 2014 11:30 pm

    I have a matched pair of Tungsram 12au7s as the outer tubes for my VTA-70. Both flash upon start-up, the right more so. They work just fine. One website used flashing as a selling point; I think it's unimportant.

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    Re: flashing pre tubes, and complete failing of same.

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