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    ST-120 Power Transformer Windings to Nowhere

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    arledgsc

    Posts : 330
    Join date : 2012-11-30
    Location : SF Bay CA

    ST-120 Power Transformer Windings to Nowhere

    Post by arledgsc on Wed Dec 18, 2013 12:42 pm

    On the ST-120 what is the purpose of the power transformer brn/yel and grn/yel windings that connect to 0.022uF caps to ground.  Is this something left over from by gone days or actually have a purpose like lowering noise?  Thanks...

    Bob Latino
    Admin

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    Join date : 2008-11-26
    Location : Massachusetts

    Re: ST-120 Power Transformer Windings to Nowhere

    Post by Bob Latino on Wed Dec 18, 2013 5:51 pm

    Those two wires ground the center taps of the two 6.3 VAC filament lines and are necessary. If you lift them from ground (through the two .022 uF caps) the amp will have an increased hum level.

    Bob

    arledgsc

    Posts : 330
    Join date : 2012-11-30
    Location : SF Bay CA

    Re: ST-120 Power Transformer Windings to Nowhere

    Post by arledgsc on Thu Dec 19, 2013 10:11 am

    Thanks Bob!  Didn't make the center tap connection but makes sense!

    sKiZo

    Posts : 1287
    Join date : 2013-04-01
    Location : Michigan USA

    Re: ST-120 Power Transformer Windings to Nowhere

    Post by sKiZo on Thu Dec 19, 2013 2:18 pm

    On a related note, wonder why we don't use variable capacitors here ...



    The capacitor is rated to minimize hum on the circuit, but it'd make sense to have some adjustment available to account for minor discrepancies?

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