What is the input impedance of a 12ax7? (at the grid) THANKS!
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Input Impedance Of 12ax7?
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It's just whatever the grid resistor is, but at high frequencies you have to take into account the Miller capacitance. That is a capacitance that appears to be from the grid to ground, and its value is equal to the grid-to-plate capacitance of the tube multiplied by the voltage gain of the stage. With a 12AX7 it can be of the order of 100pF, which is significant at high audio frequencies.
http://www.aikenamps.com/MillerCapacitance.html"Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"
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