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Old 15th November 2010, 04:11 PM   #1
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Default Ouput voltage of a triode stage on quiescent state should be zero?

Hi:

Im new to this forum and Im taking my first baby steps into this. Im interested in guitar preamps and Im learning all the theory first. One of the things that keep me thinking is the expected value of the output voltage of a triode stage in the quiescent state. I'm picturing a simple stage with a cathode with a resistor and capacitor in parallel to get the bias, and on the load side a capacitor to eliminate the DC component and a resistor to get the the voltage in the output. Should the output voltage be zero in this case or is it ok for it to have a little voltage (like 0.0x volts)?. Can anyone point me in the right direction to understand this? Thanks in advance.

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Old 15th November 2010, 05:04 PM   #2
Arnulf is offline Arnulf  Europe
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I don't understand what "resistor to get the the voltage in the output" is supposed to be but regarding your main question: quiescent voltage (left side of coupling capacitor) can never be 0V in a class A stage. Output voltage (on the right side of the coupling capacitor) will however always be 0V, assuming DC conditions on the left side.
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Old 15th November 2010, 05:10 PM   #3
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Quote:
Originally Posted by Arnulf View Post
I don't understand what "resistor to get the the voltage in the output" is supposed to be but regarding your main question: quiescent voltage (left side of coupling capacitor) can never be 0V in a class A stage. Output voltage (on the right side of the coupling capacitor) will however always be 0V, assuming DC conditions on the left side.

Thanks for your answer. With resistor on the output I meant this (I hope mi ascii art is good enough ):

Vp---| |-----+-- Vo
|
R
|
v

Vp = plate voltage
Vo = output votage
R = resistor (R is supposed to be under the "+")

Last edited by Salamander1973; 15th November 2010 at 05:13 PM. Reason: fix the ascii art
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Old 15th November 2010, 05:37 PM   #4
DF96 is offline DF96  England
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The output will not be exactly zero, but it will have small amounts of noise and hum. Good design reduces these to the point where they are not a problem, but they cannot be eliminated.
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Old 15th November 2010, 06:45 PM   #5
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Quote:
Originally Posted by Salamander1973 View Post
Im taking my first baby steps into this. Im interested in guitar preamps and Im learning all the theory first.
This site helps me a lot as I continue to learn the basics:
How to design valve guitar amplifiers
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Old 16th November 2010, 10:05 AM   #6
Arnulf is offline Arnulf  Europe
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Vo will be 0V in this case, assuming DC conditions at the Vp point )= quiescent state) and that the point below the pull-down R is grounded (your symbol implies connection to negative supply rail rather than ground).
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