The II fortys are very smooth, kinda soft edged, you love it or hate it, I'm glad you love it, they are cool little amps. Being voltage source, tube amps respond to variations in speaker impedance with different volume, aka EQ variations. The 3 way crossover nominal 6 ohms could mean it dips low and soars high, I couldn't find an actual impedance graph, you can write to them for it. Anyway, tube amps prefer flat speaker impedance, some are more tolerant than others. Quad II is autobias so don't worry about that.
Manual.http://www.stereophile.com/artdudleylistening/407listen/This review reveals your speakers' preference for higher power SS amp. You can try stuffing the bass port of the speaker to reduce the volume and tighten up the bass. Theoretically it should go lower but softer, could be just right for you. But it will change the electrical behavior of the drivers too, so listen and see. You can email Monitor to make sure stuffing the port is OK from driver cooling standpoint, or check your manual. If you know someone who is electronically savvy, You may also be able to add a parallel resistor to the bass crossover network to raise its impedance, or a zobel network to flatten an impedance peak. There is also a
Quad II Eighty available for last 2 years.
The preamp just has a dirty volume pot, it's normal maintenance. Get some of
this from RS - don't use Caig, it leaves residue. Spray it into holes in the pot inside the case. If no holes then spray it down the gap around the shaft. Turn the knob full range many times while it is wet. Let dry before running the preamp, a few minutes. Clean the source selector switch also.
Have fun!
Rich
