do tube amps have weak midbass?

i have been trying to figure out why the bass from my vk-75 sounds great on some recordings but almost disappears on others. part of the problem (i think) is a sucky AC current in my building. however, i started paying more attention to when and where the bass sucks and it seems to be primarily in midbass. the bass extention is good, such that an acoustic bass can sound very natural, but the midbass slam (?) from kickdrums and certain synth bass lines is missing.

i never noticed this "problem" with any of the SS amps i tried. is this normal for the vk-75 and/or tube amps in general? what can be done to improve it? do cables make a difference? note that i still prefer the tube sound overall...i just want to optimize my setup.

thanks.