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In Reply to: RE: grid resistors first stage of amp posted by Eli Duttman on June 24, 2012 at 16:46:55
Eli, I asked the same question as Tre did a while back assuming you read the post wrong and never got a reply. How do you figure the grid leak R as opposed to grid stop R reacts with Miller to affect HF?
Naz
Follow Ups:
C Miller combines with the grid to ground resistance to form a low pass pole. When the resistance is large and C Miller is comparatively large, F 3 of the pole will be low enough to have an effect at the top of the AF band.
IMO, it's worth noting that some units with a large I/P grid to ground resistance have a pentode I/P stage. The list includes the H/K Cit. 2, the H/K Cit. 5, and the Dyna ST70. Accident? I think NOT.
Eli D.
"The input [Miller] 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)"
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
> > CMiller combines with the grid to ground resistance to form a low pass pole. When the resistance is large and CMiller is comparatively large, F3 of the pole will be low enough to have an effect at the top of the AF band. < <
I thought there may have been confusion between grid to ground (grid leak) and series grid stopper but this confirms we are indeed discussing the grid leak R the as the statement is incorrect.
It is the series resistance including OP impedance, grid stopper and any attenuators in the chain form a low pass filter with C Miller.
The grid to ground (grid leak R) forms a high pass with any coupling cap preceding it, affecting only LF.
Tre has summed it up nicely elsewhere in this thread.
Naz
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