Bias adjustment on solid state amplifiers

Because it's a set once and forget forever issue with SS amps. Also, you aren't as much setting bias as DC offset.

Thanks @erik_squires ,

Based on your answer, why would anyone try to change bias on a SS amp? 

For the original question generally bias is set at the factory during the initial check and then again after a burn in period. Transistors and FETs don’t age the same as tubes and so while it may drift it normally wouldn’t be too much. It will drift more with temperature and line voltage than with age. Doesn’t mean it can’t be done or checked with a service manual and volt meter if one wanted to.

My experience has been that bias and DC offset are two separate adjustments. Bias sets the standing current through the output devices and somewhat the transition into class B. DC offset zeros out any DC potential between the two output terminals.