I recently stumbled across this while reading something else on the web, as you do 🙂

Somehow, he finagled the Federal Radio Commission into an “experimental” authorization for 500 kW, first with the special callsign of W8XO, finally as commercial WLW.

More at: http://www.ominous-valve.com/wlw.html

It makes pretty interesting reading, 500KW on AM is not to be sneezed at!