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How to build a constant current source using vacuum tubes

  1. Dec 2, 2009 #1
    I need to discharge a lot of current into an inductive load from a large capacitive bank. Ideally the current waveform would be as close to a flat-top as possible.

    Typically this seems to be done either by switching many caps in sequence using SCRs into a filter network to remove ripple or by simply using many caps to increase the power supply's time constant well beyond the required discharge time.

    I have toyed with the idea of using some sort of solid state regulator (e.g. zener based) but typical junction devices can't handle the currents I need (kiloamps).

    I know that large vacuum tubes are still manufactured for the radio industry etc. Would it be difficult to make a regulator or constant current source using a valve and some clever feedback? I have no idea where to start designing such a thing.
  2. jcsd
  3. Dec 2, 2009 #2


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    Transmitting valves are quite high impedance devices.
    Typically, they require very high voltages on their anodes to work properly and then they draw relatively modest currents.

    See this one:

    They use a voltage of 2000 volts or so and only get 0.4 to 0.6 amps flowing.
    Larger devices use as much or more voltage.

    I have seen advertisements for huge SCRs that will control hundreds of amps.
  4. Dec 2, 2009 #3
    Ah right, I figured these valves could handle large currents being so large.

    I'm not sure I could use SCRs to throttle kiloamps in any sort of practical (i.e. cheap) way...

    Perhaps I could use a discharge of some sort to regulate the current?
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