Tubes and light weight bass

Presumably the woofers on the Ushers are wired in parallel, so the impedance is lower at low frequencies than in the treble region. Maybe only one woofer goes up to meet the tweeter.

At any rate, a solid state voltage-source-approximating amplifier will deliver double the wattage into a 4 ohm load as into an 8 ohm load. The speakers were designed with this expectation in mind. On the other hand, a tube amp is less likely to approximate a voltage source, and therefore less likely to deliver the increased power output into low impedances that the speaker was designed to take advantage of. So in the region where the two woofers are operating in parallel, the net output with that amplifier is less than the speaker's designer intended. The result is weak bass.

That's my guess, anyway.

Duke
dealer/manufacturer

YOur tube pre (or CD player) may have inverted polarity/phase. Meaning you need to switch the +/- speaker leads at the speakers

Icorem: Just for the hell of it, I replaced (only for a short period) my PrimaLuna 6 monobocks (70wpc) with my old acurus a150 solid state amp (150 wpc) just to see what the difference would be. Besides the obvious immediate differences, I noticed the biggest change in the sound was the lack of bass the a150 had compared to the tube monoblocs.
food for thought. good luck.
jorge

Thanks for all comments so far.
I definately want to keep my tube amps for their overall advantage (to my taste - is it). I will try some of your suggestions and see if there is any improvement.
I will try playing with speaker positioning although my listening room structure is problematic.

Icorem, I own Esound CD-E5 and Dussun V8i int amp and thinking about picking up a pair of Shanling SP-80. Speaker is IRS Sigma (200 lb 3 way with ribbon mid range and tweeters). I bought Usher Be-718 Tiny Dancer on impulse hooked to Usher R1.5 but just sold it. Isn't bass strength of Esound CD-E5? Would you say CD-E5 and SP-80 was good combo for classical music? Thanks in advance.