Sonotone Model 900 Vacuum Tube Hearing Aid The Sonotone Model 900 vacuum tube hearing aid was manufactured by Sonotone International, Inc. of Ossining, New York in 1947. The Sonotone Model 900 vacuum tube hearing aid used three vacuum tubes. It weighed 5.4 oz. (154 g) without the batteries, receiver or cords. It measured 4⅜" high x 2⅝" wide by 1" thick (11.1 x 6.7 x 2.6 cm). |  | Click picture for larger view | | |   | | | |
| Front view of the Sonotone Model 900 vacuum tube hearing aid showing the microphone grill (upper center). This hearing aid had a metal front (rhodium finish) and a dark gray plastic chassis and back.
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| Close-up view of the elegant microphone grill of the Sonotone Model 900 vacuum tube hearing aid showing the bronze lyre. |  | Click picture for larger view | | | |
| Top view of the Sonotone Model 900 vacuum tube hearing aid showing the volume control wheel (left), two-pronged receiver cord plug (center) and 4-position on-off /tone control switch (right). Probably the positions were off, high tone, medium tone and low tone. The receiver, receiver cord and ear mold are missing. |  | Click picture for larger view | | | |
| Left side view of the Sonotone Model 900 vacuum tube hearing aid. |  | Click picture for larger view | | | |
| Rear view of the Sonotone Model 900 vacuum tube hearing aid showing the battery compartment door (lower half). |  | Click picture for larger view | | | |
Upper view of the back of the Sonotone Model 900 vacuum tube hearing aid showing the two slots into which the pocket clip snapped (missing).
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| Rear view of the Sonotone Model 900 vacuum tube hearing aid showing the "nameplate" in the center of the back. It shows where made (Made in U.S.A.), the manufacturer (Sonotone), the model number (900) and below that the serial number (933030). |  | Click picture for larger view | | | |
| Rear view of the Sonotone Model 900 vacuum tube hearing aid showing the battery compartment door opened and the empty battery compartment. |  | Click picture for larger view | | | |
| Close-up view of the inside of the battery compartment lid of the Sonotone Model 900 vacuum tube hearing aid showing the instructions for inserting the batteries properly in ensure their correct polarity. |  | Click picture for larger view | | | |
| Close-up view of the battery compartment of the Sonotone Model 900 vacuum tube hearing aid showing the 1˝ volt "A" battery (above) and the 22˝ volt "B" battery (below). The "A" battery was an Eveready No. 1015E (or equivalent) and the "B" battery was an Eveready No. 412E (or equivalent). |  | Click picture for larger view | | | |
| Bottom view of the Sonotone Model 900 vacuum tube hearing aid showing the 2-pronged jack for plugging in an external "A" battery. Note the holes are of different sizes so you couldn't plug the "A" battery in the wrong way.
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