Repurposing a Vintage Transistor Hearing Aid

Modern hearing aids utilize sophisticated digital signal processing (DSP) algorithms to emphasis useful sound (like a person’s voice) and minimize noise (like ambient hums). That dramatically improves a user’s ability to hear important sounds. But miniaturized DSP is a relatively new technology and older hearing aids relied on simple amplification. All they did was increase and direct overall volume (or specific frequencies, in later devices). In the early days of transistor amplification, pocket hearing aids were common. This Instructables tutorial describes how to convert a vintage pocket transistor hearing aid into an amplified microphone.

The term “transistor radio,” which you’re probably familiar with, refers to a generation of radios that took advantage of solid state transistor amplification. Transistor amplifiers replaced larger and more power-hungry vacuum tube amplifiers, making radios smaller and more portable. This also enabled the production of pocket hearing aids. Those looked a lot like transistor radios, but amplified the signal from a microphone. Depending on the model, the user could either hold the entire unit up to their ear or wear an earpiece (the more popular option, by far). These pocket hearing aids have no practical purpose today and most vintage units are almost worthless, which makes them perfect for hacking.

The goal here is to create an amplified microphone (why? That’s up to you!) and that’s essentially what the device did from the factory. So most of this tutorial is about refurbishing the vintage hardware. Early pocket hearing aids often used unusual battery sizes that aren’t easy to find today, so a lot of your work will come down to retrofitting a modern battery. You’ll also want to identify the audio output pins so you can connect a modern earbud. Finally, you’ll want to clean up the original circuitry and replace any components that have failed with age. Capacitors from that era, in particular, are prone to failure.

When you finish this work, you’ll have a small device that can amplify anything the microphone pics up and pipe that audio out to an earbud or set of headphones. This doesn’t really have any practical purpose, unless you have hearing difficulties yourself and don’t have access to modern hearing aids. But it is still cool, and that’s what matters.