Ampliphone G.R.C. 25

The G. R. C. 25 Ampliphone was a passive, acoustic loudspeaker that used a unique design to amplify sound. Instead of containing its own internal driver, the device functioned as an acoustic coupler and horn. A user would place their own set of two headphone receivers into the unit's base. The Ampliphone's polished cast aluminum body then acoustically channeled and blended the sound from both headphone drivers into a single, amplified output via its horn. This design was marketed as a way to double the volume and provide a perfect loudspeaker without the need for additional powered components.

Here you find 18 models, 12 with images and 0 with schematics for wireless sets etc. In French: TSF for Télégraphie sans fil.
All listed radios etc. from General Radio Co. Ltd.; London