The Dynaco Tube Audio Forum

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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


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    EL34 Failure

    Tubes4ever
    Tubes4ever
    Tubes4ever


    Posts : 167
    Join date : 2015-07-14
    Location : Star, Idaho
    • Post n°1

    EL34 Failure Empty EL34 Failure

    Post by Tubes4ever 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
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    10-E-C
    10-E-C
    10-E-C


    Posts : 267
    Join date : 2014-02-12
    Age : 71
    Location : upper east tn
    • Post n°2

    EL34 Failure Empty Re: EL34 Failure

    Post by 10-E-C 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
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