As tubes age, their bias point will shift. By using the BIAS KING you can maintain the sound you want by periodically adjusting the bias on your own amp. This will keep your tubes in top shape throughout their life and will keep your amp sounding its best. Use the chart provided to find out what range of current flow is acceptable for the tube type in your amp. It works on most octal socket tube amps, and requires no power source other than the amp it's plugged in to. It can also be used to match tubes into pairs. Two sockets allow you to switch between two tube readouts without having to unplug tubes.