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Original Message
RE: grid resistors first stage of amp
Posted by Tre' on June 25, 2012 at 14:34:57:
I understand Miller capacitance but it's the drive impedance vs. the Miller capacitance that causes HF loss. (They form a low pass filter.)
"Effect on frequency response
The input capacitance of the tube, in conjunction with the source impedance of the previous stage, forms a simple, single-pole RC lowpass filter with a -6dB/octave (-20dB/decade) slope, and an upper -3dB cutoff frequency equal to: f = 1/(2*pi*R*C)"
It's the source impedance not the value of the grid resistor.
Tre'