As a young lad in the late 60's I'd occasionally replace tubes in an amp when needed. In the 70's I went solid state. When I returned to the world of tube amps 20 years ago I went to replace tubes and was told "You'll have to get the amp biased". I've paid to get this done a few times. My question is, what is biasing? My other question is, how do you do it and can you do it yourself?