114
Item nr.


Blaupunkt Omniton Hearing aid

Hearing aid from the tube era.


Data for Blaupunkt Omniton
ProductionGermany, 1950.
TubesDF65, DF65, DL65.
CabinetMetal. Size 62x103x23 mm. Weight 100 gr.
PowerBatt 22.5V (B+) and 1.5V (fil.).

The Design

Tubed hearing aids have been around since the nineteen thirties. Before the days of electronics, the hearing impaired were of course simply out of business or used big horns in which people could shout to them. In the thirties, the hearing impaired was very happy with a box he could carry around, people could bend over to it and speak in the microphone and communication was established.Indeed, this picture is taken from the 1937 Lafayette Spring Catalogue In the forties came the sets one could wear `invisibly' in the vest pockets; one pocket would hold a cigar-box sized unit with three tubes and a filament battery, an equally sized pack of anode batteries would be in the other pocket. This Blaupunkt was made a few years after the invention of the transistor, but still employs tubes. The transistors were not quite ready for their job yet.

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.


Obtained12/1998 from NVHR Swap Meet, sn=118279.
Condition7.
DisposedSold 6/2018.

This Object

At first the thing didn't work, then I replaced the crystal microphone by a reproducer from one of these musical Christmas cards.
The deaf user could open a small lid on the back to insert the two batteries. It is a lot more fun, of course, to take out a screw driver and open the whole cabinet and look at the miniature three stage tube amplifier.

I tested it in September 2014 and it still worked, although the sound was rather weak (which it shouldn't, for deaf people).


Part of Gerard's Radio Corner.
Generated by SiteBuilder on 26/2/2024 by Gerard (g.tel@uu.nl)