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Vintage threads from the first ten years

previous: jason When I'm setting the bias on an amp... -- 9/7/1999 3:08 PM

Re: My finale bias question...I hope

9/7/1999 5:23 PM
SpeedRacer	Re: My finale bias question...I hope Jason: The bias does depend on the plate voltage, the current and the load (and the tube, of course!) You are correct that you are setting the operating point, which determines (in part) how the tube swings through the cycle (linearity & dissipation) and where it cuts off (how far into AB). One thing though - AB2 only means that the grid draws current during some part of an otherwise normal AB cycle.. It's still AB and one could argue that our beloved guitar amps all run AB2 since we insist on running them into grid cutoff.. If someone says that 35mA sounds best.. I think they mean for their amp, or the average amp they see on the bench.. nothing is absolute, YMMV, etc.. you need to listen first. Your amp, your tubes and your cabinet are going to have a unique solution. Knowing the "tech" end of it simply gives you a range to play around in safely, that's all. That said, most amps of a given mfr and model will be close enough in load imp and plate V that you can get into certain generalities to help you along.. a starting point at least. As far as class B, the cross over distortion will be largely a function of the output tranny quality. The right amount of "overlap" is what sounds best to you and doesn't fry the tubes.. IMHO! For more on biasing, check out www.aikenamps.com

9/7/1999 5:23 PM

SpeedRacer

Re: My finale bias question...I hope

Jason: The bias does depend on the plate voltage, the current and the load (and the tube, of course!) You are correct that you are setting the operating point, which determines (in part) how the tube swings through the cycle (linearity & dissipation) and where it cuts off (how far into AB). One thing though - AB2 only means that the grid draws current during some part of an otherwise normal AB cycle.. It's still AB and one could argue that our beloved guitar amps all run AB2 since we insist on running them into grid cutoff.. :-)

If someone says that 35mA sounds best.. I think they mean for their amp, or the average amp they see on the bench.. nothing is absolute, YMMV, etc.. you need to listen first. Your amp, your tubes and your cabinet are going to have a unique solution. Knowing the "tech" end of it simply gives you a range to play around in safely, that's all. That said, most amps of a given mfr and model will be close enough in load imp and plate V that you can get into certain generalities to help you along.. a starting point at least. As far as class B, the cross over distortion will be largely a function of the output tranny quality. The right amount of "overlap" is what sounds best to you and doesn't fry the tubes.. IMHO!

For more on biasing, check out www.aikenamps.com