Bias is the power put into a tube to push the electrons across the vacuum in the tube.
I hate to keep picking on you; but once again a technical explanation that is just too wrong to ignore. It is sort of, kind of, talking about what is happening but it is in a nutshell... wrong. I don't understand why you continue to jump in offering technical explanations about things you obviously don't completely understand.
It doesn't require a 12 page essay but it does require something that is correct, The following one sentence explanation is correct.
Bias is simply a voltage applied to a tube to control how much current flows when it is idling.
To say "power put into a tube to push the electrons across the vacuum" is flat out wrong. First of all it is not power, it is a voltage; they are not the same thing; and it is the voltage from Plate to Cathode that pushes the electrons through the vacuum not bias; bias controls how much can get through.
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