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    Live voltage from chasis of ST70

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    maninmac771

    Posts : 30
    Join date : 2011-03-07

    Live voltage from chasis of ST70

    Post by maninmac771 on Sat May 21, 2011 10:13 pm

    Hi all. Recently, I updated original quad capacitor, the PC board and the bias components (replacing selenium with diode rectifier, stock capacitors/resistors with new ones) of my Dynaco ST70. After I plugged in the power cord and tested the chasis with a screw-driver type voltage tester, the tester lights up, indicating the chasis is "live". I then unplugged, swapped the plug (the stock power cord plug doesn't have fat and narrow prongs) and plugged in again. Tested with the voltage tester again and its doesn't light up. Is there a problem or issue of concern? If yes, how to fix it? Thanks for any help.

    GP49

    Posts : 735
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: Live voltage from chasis of ST70

    Post by GP49 on Sun May 22, 2011 4:28 am

    PROBABLY no problem. There will always be one orientation of the power plug that will put the chassis closer to the 'hot' side of the AC line. This will put an AC voltage on the chassis but at a very, VERY low current; your test light will detect it but it is normally below the threshold of danger to you. The correct orientation is so that the tester does not light up, so leave it that way. It is a good idea to do this with every piece of equipment in the system with a reversible two-prong power cord; the correct orientation will yield the lowest hum.

    The situation in which you could have a hazard would be if one of the power cord bypass capacitors, connected to ground, were to become leaky. As long as you use properly-rated capacitors in this application and don't accidentally cause a short or leakage by "modifications", you should be OK; the capacitors used by the manufacturers there are special high voltage-threshold, high reliability types.

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