• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Tube amp and speaker with midbass

Sub + satellite solution is likely where all your troubles are coming from. They likely are crossed-over with high order (reactive) filter which is not ideal for a SE amp (tube or SS, really doesn't matter much).