The 18-20 uses three hi gain double triode tubes in the preamp stage and a pair of EL84 power tubes. It also is tube rectified, using a single EZ81. The EL84s are cathode biased meaning no need for bias adjusting when replacing tubes.
Channel one is specifically voiced as the "Lead" channel, while channel two is voiced for "Bass".
Each channel includes its own Tone and Volume controls. The single tone control increase bass in one direction and increases treble in the other.
Like the”1974” original it has the simplest of 2 channel preamps, one with just Tone and Volume controls, and one with added Tremolo. These feed into a cathode-biased 18W power stage, but the combination creates a dynamic and touch-responsive medium-gain amp that's perfect for blues and classic rock. At 18W, it's plenty loud enough for smaller venues and studio work.