This was the Circuit City line of MTX (same as the regular Thunder series IIRC just different heat sink) around 1998. Solid amp, still works great though not so great cosmetically (it's also missing a mounting foot). Here are some specs :
RMS Power @ 12.5v
75 watts x 2 @ 4 ohm with less than 0.05% THD
150 watts x 2 @ 2 ohm less with than 0.1% THD
300 watts bridged @ 4 ohm with less than 0.1% THD
Dynamic Power (IHF-202 standard) measured at 14.4v
425 watts bridged into @ 4 ohm
Asking $40 shipped o.b.o.