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In Reply to: RE: grid resistors first stage of amp posted by hennfarm on June 23, 2012 at 19:38:07
I like 100K to 150K. Going up to 0.5M risks grid current biasing.
At 100K versus 500K, the difference in overall db signal loss is pretty darn small, bordering on unmeasurable. The reason for higher value grid leak resistors is to be able to use lower value coupling caps as well as less high frequency degradation with long and higher capacitance interconnect runs. If you don't have those issues, the 100K is peachy.
Follow Ups:
> > as well as less high frequency degradation with long and higher capacitance interconnect runs < <
Chris, I generally agree with your other statements too but how do you figure the grid leak value affects HF?
Naz
A grid resistor of 470,000 versus 47,000 will shift down the frequency/phase effects of any tube capacitance by 10x. High pass on interconnects as well.
The grid is sitting at the output impedance of the previous stage.The value of the grid resistor will not cause HF loss.
It is the output impedance of the driving stage vs. the Miller (plus cable capacitance) that causes loss of HF.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 06/25/12
I agree generally.
Just remember that grid resistor is in parallel with the plate load of the previous tube stage.
The lower it's value, the more vertical the previous stage's load line will be.
Vertical load lines increase the harmonic distortion and decrease the gain.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
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