Eighty years ago, the December 1937 issue of Popular Mechanics carried the plans for this simple two-tube portable broadcast set. It featured two type 30 tubes, one serving as regenerative detector and the other as audio amplifier to drive a set of headphones. The set could be taken on hikes or bike rides or to the ball game. And since the set ran a long time on a set of batteries, it was said to have a definite value in flood, hurricane, or earthquake areas.
The 22.5 volt B battery would last about six months. The filaments were powered by two flashlight batteries, which would be good for about five hours at a cost of only a dime each.