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inproving safety in old hot chassis (1947)

Discussion in 'Tube Audio' started by elnaldo, Nov 10, 2018.

  1. elnaldo

    elnaldo Addicted Member

    Buenos Aires GMT-3
    Hello. Restoring this old COLLARO MICROGRAM, I see the output transformer (and speaker) is connected to mains. Parts are supposed to be "non accesible", but I'd like to know if I could improve safety in this case, if there is a way to isolate the output transformer from mains, perhaps with a properly sized safety capacitor. Actually I don't know the purpose of this connection. I'd prefer a floating output transformer if possible.

    Schematic attached:
    Collaro Microgram Circuit-V2.jpg


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  2. gadget73

    gadget73 junk junkie Subscriber

    Southern NJ
    It needs to be connected to ground to complete the negative feedback loop. You'd need a fair size capacitor to make this work, large enough that it may as well be directly connected to chassis like it already is. You could replace the power transformer with a real one instead of the autoformer that it currently uses though. That would give you mains isolation.
  3. arts

    arts Super Member

    Qc, Canada
    Yikes,a 220V hot chassis:yikes:

    Isolation transformer,no question.

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