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Attenuating power supply output volts

Discussion in 'Electronic Basics' started by garry parker, Jan 1, 2004.

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  1. garry parker

    garry parker Guest

    I need to build a power supply for a tube amp.
    My transformer has an output of 240 volts, but after rectification this
    rises to 330 volts.
    I need a supply ouput of 250v dc.
    Is there any way that I can reduce the 330 volts to 250 volts?
    The transformer is rated at 100ma, and the amp will be drawing about 65ma.
    The supply doesn't need to be regulated.

    Thanks a lot.
    Garry
     
  2. The old way was to use a choke (inductor) in series, which with the addition
    of the usual smoothing caps gave a nice clean DC. Of later years the trend
    is towards a resistor, the snag for you might be the power dissipation. At
    65mA it would be a tad over 5w so you would need a 10 watt resistor around
    the 1000 ohm mark. Perhaps an adjustable 1.5K would be ideal ?? If you have
    access to surplus suppliers or other ahem, "older" enthusiasts you may find
    something there ??
     
  3. John Fields

    John Fields Guest

    ---
    If your amp draws 65mA all the time then you could probably get away
    with a resistor either in series with the primary or in the secondary
    circuitry. If it doesn't draw 65mA all the time, then you _may_ need
    some kind of regulation depending on the voltage excursions your amp can
    take. What's your application like?
     
  4. garry parker

    garry parker Guest

    It's a class a amp so I understand it draws its full working current all the
    time.
    Garry
     
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