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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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    New VTA ST-120 Build! Need Help! SOS

    Analog Man
    Analog Man


    Posts : 56
    Join date : 2013-09-01
    Age : 61
    Location : St. Louis, MO - On The Hill

    New VTA ST-120 Build!   Need Help!  SOS - Page 2 Empty Re: New VTA ST-120 Build! Need Help! SOS

    Post by Analog Man Thu Sep 19, 2013 8:33 pm

    Bob Latino wrote:The bias voltage will never totally stabilize if you live in an area in which the LINE voltage goes up and down. Even one volt up or down will cause the bias to change. When you start the amp up COLD the bias will be a low. On start up maybe initially set all the tubes at .520 VDC or so. As the amp warms up the bias will rise slightly. You then make your final bias setting with at least 1/2 hour warm up with the amp at idle (no signal running through the amp). As long as all the tubes are between .530 and .560 VDC, you are OK. Slight bias differences between the tubes have no affect on the sound of the amp. Check the bias once a month. As the output tubes wear a little bias will change slightly.

    The thing is not to try to get all four output tubes precisely at .550 VDC (on the VTA ST-120). The 50K bias pots give great range to allow biasing many different types of output tubes > BUT they don't allow you to set each output tube at precisely .550 VDC. Getting the bias "perfect" is not really necessary .. As long as all tubes are close to the recommended setting - you are OK.

    Re: > "Should I run this amp with dummy loads and shorted input plugs for a few hours?" This is not really necessary .. Just play the amp and listen to music ..

    Bob
    Thanks Bob!
    I appreciate all of your help and especially the care you take in designing these kits and the quality! I can tell you really love what you do and you enjoy doing it. It is rare to find someone like yourself who is so dedicated and cares about quality and customer satisfaction! GOD bless you!!!Smile 

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