Eighty years ago, if you needed room filling volume from your Harmonica, there was no need for additional lung power. Instead, you could move up to the next level with electronic amplification, courtesy of this microphone shown in the April 1941 issue of Popular Mechanics. As shown here, your kids will be delighted at the prospect of this musical entertainment.

The microphone was designed to plug into the phono jack of a radio, and up to five could be wired in parallel for your next harmonica quintet performance.  The microphone was also suitable for guitar, violin, piano, and many wind instruments.  It was manufactured by the Amperite Company, then of 561 Broadway, New York.