Ouput voltage of a triode stage on quiescent state should be zero?
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 15th November 2010, 04:11 PM #1 diyAudio Member   Join Date: Sep 2010 Ouput voltage of a triode stage on quiescent state should be zero? Hi: I´m new to this forum and I´m taking my first baby steps into this. I´m interested in guitar preamps and I´m 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. Regards
 15th November 2010, 05:04 PM #2 diyAudio Member   Join Date: Feb 2009 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. __________________ mod verb, transitive /mod/ to state that one is utterly clueless about the operation of device to be "modded" and into "fixing" things that are not broken; "My new amplifier sounds great so I want to mod it."
diyAudio Member

Join Date: Sep 2010
Quote:
 Originally Posted by Arnulf 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

 15th November 2010, 05:37 PM #4 diyAudio Member   Join Date: May 2007 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.
diyAudio Member

Join Date: Mar 2007
Location: Newark, DE
Quote:
 Originally Posted by Salamander1973 I´m taking my first baby steps into this. I´m interested in guitar preamps and I´m learning all the theory first.
This site helps me a lot as I continue to learn the basics:
How to design valve guitar amplifiers

 16th November 2010, 10:05 AM #6 diyAudio Member   Join Date: Feb 2009 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). __________________ mod verb, transitive /mod/ to state that one is utterly clueless about the operation of device to be "modded" and into "fixing" things that are not broken; "My new amplifier sounds great so I want to mod it."

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