Sonotone Model 531 Vacuum Tube Hearing Aid The Sonotone Model 531 vacuum tube hearing aid was manufactured by Sonotone International, Inc. of Elmsford, New York in 1942. The Sonotone Model 531 used two vacuum tubes. It weighed 6.2 oz. (176 g) without the batteries and measured 4 1/16" high x 2 3/16" wide by 13/16" thick (10.4 x 5.6 x 2.1 cm). |  | Click picture for larger view | | |  | | | |
| Top view of the Sonotone Model 531 vacuum tube hearing aid showing the volume control/on-off switch.
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| Front view of the Sonotone Model 531 vacuum tube hearing aid. It was quite attractive with its shiny black plastic case with the pearlized inserts on the front. |  | Click picture for larger view | | | |
| Upper front view of the Sonotone Model 531 vacuum tube hearing aid showing the attractive microphone grill and pearlized inserts below it. The microphone grill of the Model 531 had 4 horizontal slots, whereas the microphone grill of the Model 533 had 5 slots. |  | Click picture for larger view | | | |
| Rear view of the Sonotone Model 531 vacuum tube hearing aid showing the metal pocket clip (top). |  | Click picture for larger view | | | |
| Top rear view of the Sonotone Model 531 vacuum tube hearing aid showing the name (Sonotone), U.S. patent number 1,679,532, "Made in U.S.A." and serial number (87612). Nowhere on this aid is the model number shown. |  | Click picture for larger view | | | |
| View of the top left corner of the back of the Sonotone Model 531 vacuum tube hearing aid showing the 4-position screwdriver adjustable tone control shown here in position 3. |  | Click picture for larger view | | | |
| Bottom view of the Sonotone Model 531 vacuum tube hearing aid showing the 4-pronged battery cable plug (left) and the 2-pronged receiver cable plug (right). |  | Click picture for larger view | | | |
Bottom view of the Sonotone Model 531 vacuum tube hearing aid showing both plugs plugged into the aid. The plugs could only be plugged in one way as the pin sizes were different so you couldn't plug them in backwards.
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| Close-up view of the 2-pronged "A" battery plug (left) and the 3-pronged "B" battery plug (right) of the Sonotone Model 531 vacuum tube hearing aid. |  | Click picture for larger view | | | |
| Close-up view of the unplugged 2-pronged "A" battery plug (bottom) of the Sonotone Model 531 vacuum tube hearing aid and the top of a 1˝ volt Sonotone No. 800X "A" battery. |  | Click picture for larger view | | | |
| Close-up view of the unplugged 3-pronged "B" battery plug (bottom right) of the Sonotone Model 531 vacuum tube hearing aid and the top of a 45 volt Burgess No. XX30E "B" battery. |  | Click picture for larger view | | | |
| Rear view of the Sonotone Model 531 vacuum tube hearing aid receiver.
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| Side view of the Sonotone Model 531 vacuum tube hearing aid receiver showing how the discrete pins plugged into the receiver.
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| Side view of the Sonotone Model 531 vacuum tube hearing aid receiver and an early custom hard clear plastic ear mold.
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View showing how the ear mold snapped to the receiver. Here shown unsnapped.
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| The Sonotone Model 531 vacuum tube hearing aid in its original leatherette carrying case. |  | Click picture for larger view | | | |
| Close-up view of the top left corner of the inside of the lid of the case of the Sonotone Model 531 vacuum tube hearing aid revealing that Sonotone called these hearing aids by the generic name of "Audicle". It reads "Sonotone Audicle" and "Reg. U.S. Pat. Off." |  | Click picture for larger view | | | |
| This card, in the pocket on the inside of the lid of the case of the Sonotone Model 531 vacuum tube hearing aid, specified a number of patents covering the design of this hearing aid. |  | Click picture for larger view | | | |
| Outside view of the Sonotone Model 531 vacuum tube hearing aid's leatherette carrying case. The case measured 6⅝" x 4 5/16" x 1 13/16" (16.9 x 10.9 x 4.7 cm).
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