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Current draw on 4, 6 or more power tubes

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  • Current draw on 4, 6 or more power tubes

    When reading current draw vai the transformer shunt method, logic tells me that I need to divide the reading by 3 when working with an amp with 6 power tubes.....3 to each side of the OT primary. Am I correct on this one?
    Any help is appreciated. I am looking at a Boogie Buster BAss 200. The amp is running well and sounding good, but I am the inquisitive type and would like to have a grip on the performance parameters....draw, plate voltages, plate dissipation and such.
    Also, for future reference, what about with an amp such as the Boogie Bass 400 with 12 6L6's....6 on a side??? Divide by 6?

  • #2
    George at Boogie confirmed my feeling that one should divide the reading by 3 in order to derive current draw per tube in this particular set-up.
    Thanks for looking.

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    • #3
      dividing by three will *not* tell the whole story. For instance, if tube #1 is drawing 52 ma, tube #2 54 ma, tube #3 75 ma, you will figure bias is 60ma per tube, when it is not! With 6 tubes in parallel push pull, or even four, you may as well put in a 1-ohm resistor in the cathode (each millivolt=milliamp across it) for individual measurement, and perhaps adjustable bias per tube. All tubes are different, and so all tubes draw different bias current for a given grid voltage or cathode resistor. You could have one dodgy tube that causes you to set the bias entirely wrong instead of replacing the tube.

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      • #4
        6267, points well made and taken, and thanks for the insight.

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