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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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    Music Stopped , Variac Fuse blue for VTA-120 Amp - fixed !

    Hops
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    Hops


    Posts : 87
    Join date : 2019-09-21
    Location : South Detroit, Michigan
    • Post n°1

    Music Stopped , Variac Fuse blue for VTA-120 Amp - fixed ! Empty Music Stopped , Variac Fuse blue for VTA-120 Amp - fixed !

    Post by Hops Mon Sep 11, 2023 7:42 pm

    Hello,

    I have a VTA-120 that I built from a kit.   I run power to it through a variac, a kilowatt, and a ground fault detector.   I use a Weber WS-1 copper cap rectifier, and a time delay relay.   Yesterday,  I was listening in another room when the music stopped -- no noise before the stop.   It appears that the variac fuse blew, as there was no voltage out of the variac.  The last time the variac fuse blew I had a bad tube rectifier.   I have a spare complete tube set ,  a spare rectifier, and of course spare fuses.     Is there anything I should check before I just change the fuse on the variac?  Any advice would be appreciated.  Thanks
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    Onlinepeterh
    peterh
    peterh


    Posts : 1861
    Join date : 2012-12-25
    Location : gothenburg, sweden
    • Post n°2

    Music Stopped , Variac Fuse blue for VTA-120 Amp - fixed ! Empty Re: Music Stopped , Variac Fuse blue for VTA-120 Amp - fixed !

    Post by peterh Tue Sep 12, 2023 2:34 am

    Hops wrote:Hello,

    I have a VTA-120 that I built from a kit.   I run power to it through a variac, a kilowatt, and a ground fault detector.   I use a Weber WS-1 copper cap rectifier, and a time delay relay.   Yesterday,  I was listening in another room when the music stopped -- no noise before the stop.   It appears that the variac fuse blew, as there was no voltage out of the variac.  The last time the variac fuse blew I had a bad tube rectifier.   I have a spare complete tube set ,  a spare rectifier, and of course spare fuses.     Is there anything I should check before I just change the fuse on the variac?  Any advice would be appreciated.  Thanks
    As you have a variac you could turn it down to zero, turn on the amp and slowly start to
    increase voltage observing the bias voltages, stopping if some bias starts to bee to high.

    But first examine resistans between bias test points and ground, it should be 10 ohm if not
    one tube has been victim om flashover and taken the resistor with it. Replace resistor and
    throw away the tube.

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    Hops
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    Hops


    Posts : 87
    Join date : 2019-09-21
    Location : South Detroit, Michigan
    • Post n°3

    Music Stopped , Variac Fuse blue for VTA-120 Amp - fixed ! Empty Thanks Peter.

    Post by Hops Sat Sep 16, 2023 6:44 pm

    Peter,
    Today I had time to follow your advice. All the resistors were in the 9 to 11 ohm range. Slowly increased the voltage to 115V, and bias stayed normal ( I run 0.45 Volts. I don't hear a difference, and I figure it gives me a little margin. I need to buy the bias display kits, but I am reluctant to modify a working amp that sounds good.

    Thanks again.

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    • Post n°4

    Music Stopped , Variac Fuse blue for VTA-120 Amp - fixed ! Empty Re: Music Stopped , Variac Fuse blue for VTA-120 Amp - fixed !

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