mixed bias

TUBESMAN · 14th January 2009, 03:13 AM

Is it possible to use fixed bias and cathode bias on a tube at the same time? I want to get part of my bias from a resistor for local feedback but also use fixed bias with a servo to keep the Ip set at a precise point.

Eli Duttman · 14th January 2009, 04:04 AM

Yes, the total bias voltage can be obtained from more than 1 source.

Combination bias can be a useful tool. You described 1 benefit, local current NFB (degeneration), which reduces distortion. Another benefit of combination bias is stabilization of the chosen operating point. Many tube types have comparatively low grid leak resistance value limits, when "fixed" bias is employed. Employing combination bias safely allows a rise in the grid leak resistor's value.

TUBESMAN · 15th January 2009, 01:19 AM

Ok, so I will give it a try. Thanks for letting me know I am on the right track.

14th January 2009, 03:13 AM	#1
TUBESMAN diyAudio Member Join Date: Apr 2004 Location: New York	mixed bias Is it possible to use fixed bias and cathode bias on a tube at the same time? I want to get part of my bias from a resistor for local feedback but also use fixed bias with a servo to keep the Ip set at a precise point. __________________ 'Musicality' is the last refuge of a tweak. --PETER ACZEL, The Audio Critic

14th January 2009, 04:04 AM	#2
Eli Duttman diyAudio Member Join Date: Apr 2004 Location: Plainsboro, NJ	Yes, the total bias voltage can be obtained from more than 1 source. Combination bias can be a useful tool. You described 1 benefit, local current NFB (degeneration), which reduces distortion. Another benefit of combination bias is stabilization of the chosen operating point. Many tube types have comparatively low grid leak resistance value limits, when "fixed" bias is employed. Employing combination bias safely allows a rise in the grid leak resistor's value. __________________ Eli D.

15th January 2009, 01:19 AM	#3
TUBESMAN diyAudio Member Join Date: Apr 2004 Location: New York	Mixed bias Ok, so I will give it a try. Thanks for letting me know I am on the right track. __________________ 'Musicality' is the last refuge of a tweak. --PETER ACZEL, The Audio Critic

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