Tube Amps Watts vs SS amp

Can someone explain is there is a difference between the watts of a tube amp vs vSS amp, Looking to get a tube amp ,but i see that the watts are much less than the SS amps, So how do these Tubes amps with 25 -70 - wpc drive these high end speakers, I have a vintage pair of AR 9s and 2 mcintosh MC2200 amps in mono (400 WPC) to drive these ,what tube amp will power these under 3-4k new or used, Thanks