John W. Campbell's The Mightiest Machine, in its first (American) paperback appearance (hardcover was in 1947.) Serialized in Astounding December 1934 to April 1935.

Aarn Munro invents a device which allows spaceships to draw broadcast power from the mightiest machine of all: the Sun! He installs this on a new ship, the Sunbeam, and is soon out in the galaxy, meeting alien races and getting involved in interstellar conflicts. This is space opera - like they use to write.