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    Tube heater delay problem

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    Rich

    Posts : 31
    Join date : 2013-01-17

    Tube heater delay problem

    Post by Rich on Sun Feb 09, 2014 1:01 am

    Hello, my ST-120 is one year old now since I finished it and it has been working flawless until now.
    V3 power tube (Left channel front KT-120) and one driver (the one close to it) shows a delay to light up heaters when I switch it on.
    After a minute or so, both heaters start to light.
    I have to say that there is no issues apart from that.
    It sounds perfect for hours.
    I've changed both tubes with same results.
    Hope anybody can help me.

    Have my best regards.

    Rich

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Tube heater delay problem

    Post by Bob Latino on Sun Feb 09, 2014 11:39 am

    Hi Rich,

    It sounds like it could be a bad solder connection on the heater wiring on pins 2 and 7 of V3. Pins 2 and 7 on V3 then feed the 6.3 VAC voltage to the left driver tube. What may be happening is after a minute or so the heat of the amp causes expansion of the solder joint to make the connection.

    Resoldering both pins 2 and 7 on V3 should get rid of your delayed heater lighting.

    Why did this not happen when you first started the amp up a year ago? Sometimes after many on/off cycles (heating up and expansion then cooling off and contracting) a solder connection can break and you lose the connection even though the connection LOOKS good.

    Bob

    Rich

    Posts : 31
    Join date : 2013-01-17

    Re: Tube heater delay problem

    Post by Rich on Sun Feb 09, 2014 3:19 pm

    Thank you very much Bob!
    It is time to have a look inside after a year.

    Have my best regards from Mexico!

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