Bias King Pro As tubes age, their bias point will shift By using the BIAS KING&#153; 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