114
Item nr.
Hearing aid from the tube era.
Production | Germany, 1950. |
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Tubes | DF65, DF65, DL65. |
Cabinet | Metal. Size 62x103x23 mm. Weight 100 gr. |
Power | Batt 22.5V (B+) and 1.5V (fil.). |
During the Second World Wide Slaughter, subminiature tubes, also called pencil tubes because of their diameter, were developed. Thus around 1950 one would find units as small as this one. Later still came the transistorized units that were even smaller and the batteries would last a lot longer. The Omniton is powered by a 22.5V cell for the plate voltage. These batteries are now called Photo Cells and are still available, one of them should provide some 80 hours of service. Observe the three small tubes in the picture.
For the more technically interested, here is a close-up of the miniature pentode tube and the schematic diagram. The unit is a three stage amplifier with volume control after the first stage. The crystal earset is connected directly to the plate of the output tube, but an output transformer is also built in, just in case if somebody wants to connect a magnetic headset. The filaments are supplied from a penlight battery. The two signal pentodes require 13.3mA at 0.625V and are supplied in series from the battery. The DL65 output tube takes 13mA alone from 1.25V. Its plate current is 0.46mA and it can deliver 1.6mW of output power.
Obtained | 12/1998 from NVHR Swap Meet, sn=118279. |
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Condition | 7. |
Disposed | Sold 6/2018. |
I tested it in September 2014 and it still worked, although the sound was rather weak (which it shouldn't, for deaf people).