Tweet
What is the input impedance of a 12ax7? (at the grid) THANKS!
-
-
It depends on the 12ax7 - look up the datasheet from the manufacturer of the tube in question. The datasheet will have TONS of other useful information as well.
I think the standard value used for a generic 12ax7 is 1 megohm -
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?"Comment
Comment