Audio Signal Injector

This decades-old audio signal injector was wired on a piece of perfboard.  All components were sourced from the junk box.
Audio Signal Injector
The enclosure was fashioned from an empty tapered spool of industrial sewing thread, a cosmetic tube cap and a film canister cap on which the push button switch was fixed.

A machine screw, filed to a point and fixed to the cosmetic tube cap, served as the prod.

Audio Signal Injector - Schematic
Over the years, this unit has helped service the audio stages of several ham rigs.