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    EL34 Failure

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    Tubes4ever

    Posts : 61
    Join date : 2015-07-14
    Location : Star, Idaho

    EL34 Failure

    Post by Tubes4ever on Tue Jan 12, 2016 6:04 pm

    I have a quad set of Russian Mullard Reissue EL34s in my ST70.  I've had them since July. About 40 hours a week usage.

    This morning when I turned the amp on, the left channel immediately started to pop and scratch. The left front tube began red plating rather brightly.  I turned off the amp and moved the red plating tube to another socket.  I turned the amp back on and the same tube began to red plate again.  Obviously a bad tube.  This tube was running fine the day before.  Seems like the last thermal cycle caused the grid to short to the cathode.

    Fortunately I have a spare EL34 that is running fine now.

    I know we all have tube failures, but I just wanted to note how we shouldn't just turn on the cold amp and walk off.  If I hadn't been there to see the failure on startup, I may have damaged the output transformer or other components.

    Tim

    10-E-C

    Posts : 86
    Join date : 2014-02-12
    Age : 63
    Location : upper east tn

    Re: EL34 Failure

    Post by 10-E-C on Tue Jan 12, 2016 9:53 pm

    Tubes4ever wrote:I have a quad set of Russian Mullard Reissue EL34s in my ST70.  I've had them since July. About 40 hours a week usage.

    This morning when I turned the amp on, the left channel immediately started to pop and scratch. The left front tube began red plating rather brightly.  I turned off the amp and moved the red plating tube to another socket.  I turned the amp back on and the same tube began to red plate again.  Obviously a bad tube.  This tube was running fine the day before.  Seems like the last thermal cycle caused the grid to short to the cathode.

    Fortunately I have a spare EL34 that is running fine now.

    I know we all have tube failures, but I just wanted to note how we shouldn't just turn on the cold amp and walk off.  If I hadn't been there to see the failure on startup, I may have damaged the output transformer or other components.

    Tim

    I read a quote on this forum once " Never turn your back to those bastards! Good advice as you can testify.

    TM

      Current date/time is Sat Dec 03, 2016 5:38 am