Bias Adjustment

Fixed Bias Auto/Self Bias

 


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Last Edited:
12-Sep-2004

 
There's probably more misunderstanding and opinions about how to properly bias a tube amp than any other area of tube lore. Everybody seems to find a "secret" shortcut that magically turns a "dead" sounding amp into the sweetest sounding amp they're ever heard.

In fact, a reverse analog is more true. Bias is a little like setting the idle on a car. You can't make a Ford into a Ferrari, but you sure can make a Ferrari run like a Ford.

Remember that the Brits call these firebottles "Valves" with good reason. The tube's control grid is like a faucet, with the bias voltage like the handle. As you open the faucet by applying more and more positive (Bias) voltage, more electrons flow, and ultimately you hear music. It's simply about control, that's all.

A lot of other problem areas can exist in an amplifier that no amount of bias adjustment can fix. But we still tend to focus on the biasing because it's where the "rubber meets the road."

!CAUT!ON!  Improper Biasing may result in the following:

Damage to the power tubes themselves
Decrease the life expectancy of the power tubes
Damage to amplifier's grid resistors
Damage to the output transformers within the amplifier (ouch!)
Damage to amplifier Power supply circuitry and transformer

So what's all the fuss? Follow these steps and you'll be properly biased in no time.

 

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