My guitard player just bought a $3000 Mesa Boogie tube rig with 2 12's. I must say I was quite impressed. Enough in fact I would like to replace my Hartke LH500 with a comparable tube bass amp and give it a try because.. Life is short. They say that there is a difference between tube watts and solid state watts. What tube head would you suggest for two Hartke Hydrive 12 cabs.