Bias adjustment on solid state amplifiers

@richfrankOften tube amp bias is measured across a resistor scaled to convert mV to mA.

500mA is a pretty hefty tube bias. 50-70mA is more like it.

What kind of amp?

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

Not true. Bias is applied to both sides, so current increases, but net voltage remains zero.

IMO, bias drift accounts for varying sonics in SS amplifiers. Bias drifts with temperature. Service manuals often have voltage spec, but no °C or how and where measured. Bias an amp that's been idling for 20 minutes and then measure it after Zepping for an hour and the values will be radically different. Add in one or two 10°C ambient changes for open top on a workbench in an air conditioned factory and a buttoned up amp in a rack and the delta is even larger.

This is why fuse changers hear such 'UGE differences. Neither their ears nor the electronics are in the same state.

Depending on where the feedback device is located, there may be a considerable time lag to the thermal compensation device. Consequently, many designs are under biased to preclude thermal runaway.

Transistors with on-die bias diode offer better performance at low signal levels, just where most of the music resides.