Sonotone Model 333 Behind-the-Ear (BTE) Transistor Hearing Aid The Sonotone Model 333 behind-the-ear hearing aid was manufactured by Sonotone International, Inc. of New York in 1957. It was an unusual and weird-looking hearing aid. It contained 3 transistors and used a No. 400 battery. The slit on the end reveals the serial number. |  | Click picture for larger view | | |   | | | |
| Top view showing the microphone port (left center), the battery compartment (middle) and the receiver connection (right).
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| Rear view of the Sonotone Model 333. |  | Click picture for larger view | | | |
| Bottom end view of the Sonotone 333. |  | Click picture for larger view | | | |
| The Sonotone Model 333 with an ear mold attached. If you had never seen the patent application, you would not suspect this was really a BTE aid rather than some strange body aid. |  | Click picture for larger view | | | |
| Picture of a different Sonotone Model 333 (not in museum) with an ear mold configured for use as a BTE hearing aid. Note that the battery door (which is missing in all the other pictures) is present. |  | Click picture for larger view | | | |
| Another view of the Sonotone 333 showing just how "clunky" this BTE aid was.
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