Radioear B-7B Carbon Hearing Aid The Radioear B-7B carbon hearing aid was manufactured by E. A. Myers & Sons, Ltd. of Pittsburg, PA in 1931. The B-7B transmitter (microphone), shown in the pictures, measured 3⅜" in diameter, while the B-7A (a similar model) was slightly larger measuring 3˝” in diameter. The carbon transmitter (microphone) plugged onto a battery case that held two “C” size batteries, or it could be plugged directly onto a Radioear battery. The operating voltage was 3 or 4˝ volts depending upon the amount of power required for a given hearing loss. A small black miniature receiver, onto which an ear mold was clipped, plugged into the transmitter.
Typically, the Model B-7A came with an air conduction receiver, while the Model B-7B came equipped with a bone conduction receiver (although here the B-7B is shown with the air conduction receiver).
|  | Click picture for larger view | | |  | | | |
| The front of the Radioear B-7B transmitter (microphone) showing the on-off switch/rheostat volume control (left). It is in the off position. Down all the way would be the loudest volume. On the right side is a "Tel/Voice" switch. Moving the Tel-Voice switch to the “Tel” position opened up the 5 screened holes in the centre of the transmitter so that a telephone receiver could be held directly against the carbon transmitter. When in the “Voice” position, the sound entered the carbon transmitter through the six slots located around the circumference of the transmitter.
|  | Click picture for larger view | | | |
