TRANSISTOR MUSEUM™ Historic Transistor Photo Gallery
Transistor Size (3/8”H X 1/8”OD) Date Code 540 (1955 Week 40) Internal View of 1950s Acousticon Hearing Aid	RAYTHEON CK726 TYPE Germanium PNP Alloy Junction USAGE Hearing Aids DATE INTRODUCED 1955 CASE STYLES Blue Painted Metal AVAILABILITY Limited (Hearing Aid Usage)
HISTORIC NOTES Raytheon dominated the early transistor hearing aid market with the introduction of the CK718 in 1952. This was the first commercial transistor to be produced in high volume and it was used in thousands of the hearing aids produced throughout the 1950s. These first Raytheon CK718 hearing aid transistors were crudely made, using a black epoxy case which was not an effective seal against moisture penetration. Raytheon made rapid improvements to their transistor manufacturing processes, and introduced much more robust, metal cased hearing aid transistor types in 1954 and 1955. The most unique of these devices was the CK726; this type was very short-lived and is easily identified by the thin cylindrical case style. The Raytheon designers quickly standardized on the more compact CK78X cased style and the CK726 remains the only known Raytheon type using the cylindrical case. Shown above is an internal view of an Acousticon hearing aid, using both transistor metal case styles. The relative scarcity of the CK726, and the unique graceful styling of the case style, contribute to the historical importance of this Raytheon device.
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