BASE. 2 3-500ZG TUBES ALSO HAS A HEAVY DUTY 1/2+ AMP POWER TRANSFORMER SURGE TO 1 AMP. WITH INPUT AND OUTPUT TUNING. bias diode voltage dropping assembly, The assembly is used in For CT circuit of the RF chassis to set bias to the tubes. This adjusts the resting current of the amplifier and sets the class of operation. This amp is ran on 120 volts AC with a 20 amp of draw. 20 watts key and 180 watts peak input drive gave me 500+ watts RMS and 1800 + peak....BIG AUDIO. I have heard of others driving more watts in to this model of amp and seen more watts but that is all up to you