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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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    NOS Mullard 12au7 Lights up bright inside tube on start up but amp seems to play fine.

    Midwestside
    Midwestside
    Midwestside


    Posts : 78
    Join date : 2019-03-20
    • Post n°1

    NOS Mullard 12au7 Lights up bright inside tube on start up but amp seems to play fine. Empty NOS Mullard 12au7 Lights up bright inside tube on start up but amp seems to play fine.

    Post by Midwestside Mon Apr 27, 2020 3:34 pm

    Bought an NOS Mullard 12au7 on the auction site for the center driver position on my VTA 70.
    Plugged it in, flipped the power on and i saw a bright orange glow inside the tube.
    It glows bright and then disappears in like 2 seconds.
    I turned off the amp and restarted it again a few times. seems to repeat the flash each time.
    I notice the filaments glowing in the bottom of the tube right about where they spit off the socket pins in a couple of places
    after the amp warms up .
    Music seems to play fine and actually sounds pretty nice.
    Just wondering if some tubes start this way or is it a tube that is about to be a dud?
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    Dave_in_Va
    Dave_in_Va
    Dave_in_Va


    Posts : 443
    Join date : 2013-04-02
    Location : Mid. VA
    • Post n°2

    NOS Mullard 12au7 Lights up bright inside tube on start up but amp seems to play fine. Empty Re: NOS Mullard 12au7 Lights up bright inside tube on start up but amp seems to play fine.

    Post by Dave_in_Va Mon Apr 27, 2020 3:37 pm

    That's the way they (mostly European tubes) work. It's normal. And cool!

    Don't turn your amp on and off quickly. You'll blow the rectifier.
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    Midwestside
    Midwestside
    Midwestside


    Posts : 78
    Join date : 2019-03-20
    • Post n°3

    NOS Mullard 12au7 Lights up bright inside tube on start up but amp seems to play fine. Empty Re: NOS Mullard 12au7 Lights up bright inside tube on start up but amp seems to play fine.

    Post by Midwestside Mon Apr 27, 2020 3:44 pm

    Dave_in_Va wrote:That's the way they (mostly European tubes) work. It's normal. And cool!

    Don't turn your amp on and off quickly. You'll blow the rectifier.

    Sorry, yeah, i went searching in the meantime on google and found this out.
    Dont worry, i waited several minutes between each power on/off cycle.
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    DavidR
    DavidR
    DavidR


    Posts : 156
    Join date : 2017-08-10
    Location : MetroWest, MA
    • Post n°4

    NOS Mullard 12au7 Lights up bright inside tube on start up but amp seems to play fine. Empty Re: NOS Mullard 12au7 Lights up bright inside tube on start up but amp seems to play fine.

    Post by DavidR Mon Apr 27, 2020 8:12 pm

    I have a NOS Mullard 12AX7A and some NOS Tungsram and 12AU7A that flash on start up. Quite normal for many European tubes.

    Does anyone know if Telefunken 12AX7 tubes flash on start-up? I have one that doesn't .


    Last edited by DavidR on Tue May 19, 2020 8:21 pm; edited 1 time in total
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    New2Tubez
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    New2Tubez


    Posts : 184
    Join date : 2018-03-20
    Location : NY
    • Post n°5

    NOS Mullard 12au7 Lights up bright inside tube on start up but amp seems to play fine. Empty Re: NOS Mullard 12au7 Lights up bright inside tube on start up but amp seems to play fine.

    Post by New2Tubez Mon Apr 27, 2020 10:18 pm

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    Midwestside
    Midwestside
    Midwestside


    Posts : 78
    Join date : 2019-03-20
    • Post n°6

    NOS Mullard 12au7 Lights up bright inside tube on start up but amp seems to play fine. Empty Re: NOS Mullard 12au7 Lights up bright inside tube on start up but amp seems to play fine.

    Post by Midwestside Mon Apr 27, 2020 10:37 pm

    New2Tubez wrote:Have a look at this...

    https://www.youtube.com/watch?v=bX0o3jAzSBs

    Quite interesting!
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    • Post n°7

    NOS Mullard 12au7 Lights up bright inside tube on start up but amp seems to play fine. Empty Re: NOS Mullard 12au7 Lights up bright inside tube on start up but amp seems to play fine.

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