The Superdrive series amps were designed by Jeff Bober with the preamp section co-designed by the one and only Dave Friedman. This is an absolutely killer sounding and feeling amp. Rich and 3D sounding with plenty of gain on tap and a stellar sounding clean.
The SD45 runs two 6L6 or KT66 power tubes (this one has 6L6s), three 12AX7 preamp tubes, and a 5AR4 rectifier tube.