Concealed Hearing Devices of the 20th Century (Part 2)

Part 2 DEAFNESS IN DISGUISE

Concealed Hearing Devices of the 20th Century

The introduction of vacuum tubes in the early 1920s was a major technological step in the evolution of electrical hearing aids. Vacuum tubes provided a much more efficient method of amplifying electrical signals. This efficiency translated into greater acoustic gain and hence, yielding greater benefit for hard of hearing and deaf users.

Precision Table Aid, 1948
Like the early carbon electrical models, early vacuum tube hearing aids were large, fragile, not easily transported, and camouflaged designs were confined to tabletop appliances like this "radio."

Zenith Radionic A2A, 1944
During the 1930s and 40s, manufacturers developed body-worn designs that housed vacuum tubes and microphones within a single unit, which allowed for portability. These early body-worn vacuum tube hearing aids were cumbersome and required wires to connect the batteries and the earpiece to the microphone/amplifier unit.

Wearable Batteries
As seen in these images, hearing aid batteries were at least as large as the other components and weighed up to 2.5 pounds. Users wore batteries in cumbersome battery holders under their clothes or in pockets with straps, and multiple thick cords connected the batteries to the microphone/amplifier unit and earpiece.

The miniaturization of the vacuum tube and the invention of the transistor in 1947 led to even more dramatic size reductions. Now, the microphone, amplifier, and batteries could be packaged in one unit with a single cord to the earpiece. For a woman, the hearing aid cord could be a pearl necklace, the receiver an earring, and the microphone a brooch or pendant.

Zenith Model 75, 1947
The Zenith Model 75 represents one of the earliest models incorporating the microphone, amplifier, and batteries within a single unit.