Updating old electronics with 3 prong power cable

Discussion in 'The Projects Forum' started by fairchild, Sep 20, 2009.

  1. fairchild

    Thread Starter New Member

    Sep 20, 2009
    I have this old Sony tube pre-amp that i would like to add a ground wire to, but i'm uncertain where the Black and White wires go.

    I know the Green is ground....i would like to know the best place to attach this to the chassis.

    On the original 2 prong chord...one lead goes to the fuse....the other goes to the power switch, which then goes to the power transformer.

    Also not sure if the amp needs any other modifications. Any help would be greatly appreciated.

    Thank You!
  2. SgtWookie


    Jul 17, 2007
    Not a bad idea!

    One of the nuts that attaches the transformer to the chassis would be a likely place. Make sure you scrape off any insulating lacquer or other clear coating. If that isn't convenient, drill through the chassis near the fuse (making certain you don't drill through anything, and don't leave any metal bits inside the case) and then secure it using a locknut and panhead screw.

    That's rather odd. Is the original plug polarized? eg: one prong is wider than the other? If so, the wider prong is Neutral (white), the narrow prong is Hot (black).

    Normally, the Hot (black) goes directly to the fuse, then from the other side of the fuse to the power switch, and then to the transformer. You wouldn't want the Neutral line to be fused.
  3. fairchild

    Thread Starter New Member

    Sep 20, 2009
    Both prongs on the original cable are the same. The wires are not colored.

    it looks like the other side of the fuse has a wire going into the transformer.

    This thing may have been modified. Which is weird because i thought modifications were to improve. This amp has extremely low level unless i'm touching my finger to the chassis (which i guess is grounding it?)

    Thanks for your help!
  4. Wendy


    Mar 24, 2008
    One last thought, you can get a HP power cord socket pretty easily (I have a box of em). This would allow you to remove the power cord, making transport much easier, and if the power cord wears out you can replace it easily.
  5. GetDeviceInfo

    AAC Fanatic!

    Jun 7, 2009
    A SgtWookie indicated, it is common practice to tie your ground to the transfomer lug. However, the intent is to bond the outer most metallic housing, or the housing that your most likely to come in contact with, to ground. In some of this odler equipment that wasn't grounded, continuity through it's housings where not paramount. You may want to consider adding a jumper from that lug to the outer most metalic housing with a pan screw or similar, unless it's clearly continous.