KLH Model 5 question

Those vintage AR and KLH acoustic suspension speakers were built back in the day when 25 watt (PP 6L6G's) tube amps were common. These sealed-box speakers sacrificed sensitivity for lower bass extension. Which they do quite well! 

Twenty five watts is a good recommendation! My KLH 6's work well with my Dynaco ST70 tube amp (35 wpc).

I have AR 2ax's, AR 4's and KLH 6's. Plus the outstanding KLH Nine electrostats. They are all capable of excellent well-balanced sound!