From Tiny Tubes to Transistors: In the late 1940s, Raytheon was the major supplier of subminiature vacuum tubes to the hearing aid industry. These small, pencil-sized tubes had been developed in 1938, and supplied to the hearing aid industry starting in 1939. After the war, Raytheon continued to improve on the design of these small tubes. By developing low-current versions of these tubes, Raytheon was able to provide manufacturers with a product which could extend the life of the expensive batteries required to power hearing aids. This technology reached a peak in 1952 with hearing aids such as the Zenith Royal, which used three tiny Raytheon subminiature tubes. In the early 1950s, transistor technology seemed ideally suited for applications such as hearing aids. Transistors were small, light weight, rugged and, most importantly, used much less power than did vacuum tubes. Spurred by the invention of junction transistor technology at Bell Labs in 1951, Raytheon began development of a junction transistor that would be suitable for hearing aid use. By mid to late 1952, Raytheon had successfully implemented the alloy-junction process for transistor manufacturing, and by December 1952, over 2000 functional transistors per day were being manufactured. In addition, Raytheon worked closely with major hearing aid manufacturers such as Maico, Zenith and Sonotone to develop transistor or hybrid (tube and transistor) models to be available in 1953 - the Raytheon CK718 was the first mass produced junction transistor; it was not made available to the general public, but was supplied exclusively by Raytheon to over a dozen hearing aid manufacturing companies. The Zenith Royal T, the Sonotone 1010 and the Maico Transist-ear are all examples of hearing aids from 1953 which used the CK718.





On the right are submini tubes used in a Zenith Royal hearing aid. The 201 date code represents week 1, 1952. On the left are examples of CK718 junction transistors used in the Zenith Royal T hearing aid, with 252 representing week 52, 1952. In less than one year transistors had replaced the dominant vacuum tube technology in hearing aids.




COPYRIGHT 2003 by Jack Ward. All Rights Reserved.