Biasing involves setting the idle rate of your output valves.
If the idle is set too low the amp will sound flat and grainy. Too high and the amp will sound mushy (in extreme cases the valves will glow cherry red like xmas-tree lights and die, possibly taking other components with them).
That said there is a fairly wide range of idle currents where you could consider the amp biased correctly. It's a tradeoff between output, tone and lifespan of your valves.
An overbiased amp (cold bias) will generally sound grainy, but your valves will last longer.
An underbiased amp (hot bias) will sound more compressed and your valves will wear much quicker.
:twisted:
