The CK722 was the first low-costjunction transistor available to the general public. It was a PNPgermaniumsmall signal unit. Developed by Norman Krim, it was introduced by Raytheon in early 1953 for $7.60 each; the price was reduced to $3.50 in late 1954 and to $0.99 in 1956. Norm Krim selected Radio Shack to sell the CK721 and CK722 through their catalog. Krim had a long-standing personal and business relationship with Radio Shack. The CK722s were selected "fall out" from the Raytheon's premium-priced CK721. Raytheon actively encouraged hobbyists with design contests and advertisements. In the 1950s and 1960s, hundreds of hobbyist electronics projects based around the CK722 transistor were published in popular books and magazines. Raytheon also participated in expanding the role of the CK721/CK722 as a hobbyist electronics device by publishing "Transistor Applications" and "Transistor Applications- Volume 2" during the mid-1950s.
Construction
The original CK722 were direct fallouts from CK718 hearing aid transistors, that did not meet specifications. These fallouts were later stamped with CK721 or CK722 numbers based on gain, noise and other dynamic characteristics. Early CK722's were plastic encapsulated and had a black body. As Raytheon improved its production of hearing aid transistors with the introduction of the smaller CK78x series, the body of the CK721/CK722's was changed to a metal case. Raytheon, however kept the basic body size and used a unique method by taking the smaller CK78x rejects and inserting it into the larger body and sealing it. The first metal-cased CK721/CK722's were blue and the later ones were silver. More details of this can be found in Jack Ward's website, Semiconductor Museum or the CK722 Museum- see external link reference below.
Norman Krim – Father of the Transistor Hobbyist Market
In the late 1930s, Norm Krim, then an engineer for Raytheon, was looking into subminiature tubes for use in consumer applications such as hearing aids and pocket radios. Krim's team developed the CK501X subminiature amplifier tube that could run on penlight A type batteries or small 22.5 V B type batteries. Following World War Two, Krim was interested in developing the first pocket vacuum tube radio. Raytheon approved, and a team headed by Krim designed a set of subminiature tubes specifically for radios. Raytheon’s acquisition of Belmont Radio proved prescient, and the result was the Belmont Boulevard in 1945. Unfortunately the radio did not sell well and Raytheon took a loss. Despite this setback, Krim remained at the company and shifted his attention to the newly developed transistor.
Carl Todd, a hobbyist and later engineer GE’s transistor division, placed 6th in Raytheon's CK722 design contest. His hobby work with this early transistor inspired him to pursue electrical engineering as a career. As an engineer, he helped develop the 2N107 transistor, GE's alternative to the CK722.
