I've just bought a Line 6 HD300 and want to use it as a preamp for my 1970s 60 watt Boogie Mk 1, # A652, bypassing the preamp stage so that I can use the power amp only. It has a beige vinyl covered cabinet, a cloth face and is equipped with a 12" Altec-Lansing 417-8H Series II speaker. It's...