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That's Not Correct

"The grid draws net current, since it only conducts on positive peaks. This current must come from the bias supply in the end."

No, when excitation drives the grid positive, the current path is from the grid, through the transformer secondary and into the bypass capacitor at the cold side of the secondary. The increased average current that you ascribe to the bias supply is in fact increased average current provided by the driver tube. This is the reason the driver tube in a Class A2 amplifier must deliver power, not just voltage.

It's worth noting that the bypass cap and the bias supply do in fact form a parallel sink for grid current. However, if the bias supply itself includes the typical high equivalent internal resistance, and that resistance is feeding a large, high quality bypass cap at the cold side of the transformer, current rise through the bias supply as a result of grid current will be on the order of tens or hundreds of microamps.




Edits: 09/06/14
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