Acousticon A-90 (Imperial) (1-piece) Vacuum Tube Hearing Aid The Acousticon A-90 (Imperial) vacuum tube hearing aid was produced by Dictograph Products, Inc. of New York in 1947. This version of their Model A-90 was their first 1-piece body hearing aid. It featured a different style case than the 2-piece A-90. The 1-piece version was contained in a polished anodized aluminum case with light brown enamel on the left two-thirds of the front. The hearing aid measured 4 1/16” by 2⅜” by ¾” and weighed 4.2 oz. without the batteries. |  | Click picture for larger view | | |   | | | |
| Rear view of the 1-piece Acousticon A-90 showing the make and model number (left) and the swing out battery door (right). The back and the front right side of the case are polished aluminum. (In contrast, the Acousticon A-90M was anodized gold-colored aluminum.)
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| Rear view of the 1-piece Acousticon A-90 showing the make (Acousticon) and model number (A-90).
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| Upper front view of the 1-piece Acousticon A-90 showing the microphone grill. Note that the grill is set flush to the case. (The Acousticon A-90M had the same grill but it was recessed a bit).
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| Top view of the 1-piece Acousticon A-90 showing the on-off/volume control (left), the two screws to hold the pocket clip in place (pocket clip not shown) and the two holes with the receiver cords plugged into them. (center). At this point, Acousticon did not use plugs—just pins on the ends of the cords. |  | Click picture for larger view | | | |
| Left side view of the 1-piece Acousticon A-90 showing the 4-position tone control. To the right is the serial number (F989). |  | Click picture for larger view | | | |
| The battery compartment of the 1-piece Acousticon A-90. |  | Click picture for larger view | | | |
| The 1-piece Acousticon A-90 was the first Acousticon hearing aid to be powered by internal batteries—a 1.4 volt 4Z mercury "A" cell (left) and a 15 volt Eveready 411E "B" battery (right). |  | Click picture for larger view | | | |
| The 1-piece Acousticon A-90 used a rare size of "A" battery that was the same diameter as the much more common RM-4, but was not as thick. The 4Z battery fit the battery compartment just fine. |  | Click picture for larger view | | | |
| If you tried to use the common RM-4 size of battery in the 1-piece Acousticon A-90, it just wouldn't fit. |  | Click picture for larger view | | | |
| The Mallory RM-4 battery (left) in comparison to the 4Z battery (right). When you compare the two you can see why the RM-4 won't fit in this hearing aid.
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