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10-10-2019, 07:11 PM
They sure do! But then when things are right, I'm amazed at how accurate they are.
And no, I don't think this is something that is inherent in the design or that I have super ears or anything, this is not typical.
While the "off" tubes do seem to be driven and their configuration seems to affect things, I don't think this is the root cause. Now that I figured out how to see it on a scope, it's clearly crossover distortion.
I'm convinced we're onto it and that it's caused by the bias regulator somehow. I took some data plotting Vs, -Vb and Ik while scaling downward and Ik seems to drop below the ideal line (Imax to 0) on the transfer characteristics...which is worse considering Ik includes the screen current (which should skew the points upwards, not down)!
And one other odd observation was that with the power scaling set to minimum (Vs=52.24V), I tried to see if I could bias out the crossover distortion but found I had a range of only 1mA (4-5mA). That seems odd to me. While I'd expect the available range to be restricted, 1mA is tiny. Got a feeling that is part of this.
And no, I don't think this is something that is inherent in the design or that I have super ears or anything, this is not typical.
While the "off" tubes do seem to be driven and their configuration seems to affect things, I don't think this is the root cause. Now that I figured out how to see it on a scope, it's clearly crossover distortion.
I'm convinced we're onto it and that it's caused by the bias regulator somehow. I took some data plotting Vs, -Vb and Ik while scaling downward and Ik seems to drop below the ideal line (Imax to 0) on the transfer characteristics...which is worse considering Ik includes the screen current (which should skew the points upwards, not down)!
And one other odd observation was that with the power scaling set to minimum (Vs=52.24V), I tried to see if I could bias out the crossover distortion but found I had a range of only 1mA (4-5mA). That seems odd to me. While I'd expect the available range to be restricted, 1mA is tiny. Got a feeling that is part of this.
