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CK722 transistor and package

The CK722 was the first low-cost junction transistor available to the general public. It was a PNP germanium small 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.[1] The CK722s were selected "fall out" from the Raytheon's premium-priced CK721 (which are fallouts from CK718 hearing-aid transistors).[2] Raytheon actively encouraged hobbyist with design contest and advertisements.[3][4]

In the 1950s and 1960s, hundreds of hobbyist electronics projects based around the CK722 transistor were published in popular books and magazines.[5][6] 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.

Transistor application books for CK722 by Raytheon
Size comparison and metal case colors of Raytheon hearing aid transistors on the left and the CK721 (Blue) and CK722 (Silver)on the right. The rejected hearing aid transistors would be inside the metal cases of the CK721 and CK722.


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.

Engineers associated with the CK722[edit]

Norman Krim – Father of the CK722 Who Launched the Transistor Hobbyist Market[edit]

Norm Krim has always been involved with miniaturization electronics. In the late 1930s Krim then an engineer for Raytheon was looking into using subminiature tubes developed for military equipment to be used in consumer applications such as hearing aids and of course pocket radios. Krim proposed to Raytheon's president Laurence Marshall that for about $25,000, Raytheon can develop a compact hearing aid. Krim's group developed the CK501X subminiature amplifier tube that can run on penlight A type batteries and a small 22.5 V B type battery. Raytheon became a major supplier of hearing aid vacuum tubes.

After World War Two, Krim wanted to make the first pocket vacuum tube radio. After his success with hearing aids, Raytheon gave him the go ahead. As a result, his group design a set of subminiature tubes for radios (2E32, 2E36, 2E42 and 2G22). Raytheon bought Belmont Radio allowing Raytheon to have firm control of design. The result was the Belmont Boulevard in 1945. The radio did not sell well and Raytheon took a loss. Norman Krim's job was on the line but somehow he manage to stay on and thanks to Raytheon's trust in him he help the company into a much bigger market, the transistor.[7]

To follow Norm Krim's transistor achievements for Raytheon check the following sources:

Jack Ward's Semiconductor Museum and IEEE Spectrum article "In Memoriam of Norman Krim" See the External Links section.

Carl David Todd – Participant in the CK722 Design Contest[edit]

Carl Todd a hobbyist and later engineer at GE Transistor division placed 6th in Raytheon's CK722 design contest. He won $100. The CK722 was partly responsible for his interest in becoming an engineer. His interest as a hobbyist and engineer would permit him to conceive the 2N107 transistor, GE's alternative to the CK722.[8]

See also[edit]


  1. ^ Ward, Jack. "Norm Krim- The Father of the CK722". 
  2. ^ Garner, Lou (October 1979). "Solid State: Down Nostalgia Lane". Popular Electronics. Vol. 16 no. 4. New York: Ziff-Davis. pp. 86, 87, 92. 
  3. ^ "$10,000 in Prizes. Enter Raytheon's Transistor Application Contest!". Popular Mechanics. Vol. 99 no. 6. Chicago: Popular Mechanics Co. June 1953. p. 219. ISSN 0032-4558.  Raytheon sponsored a design contest for applications that used the CK722 transistor. The top prize was $5,000.
  4. ^ "8 Transistor circuits you build with Raytheon CK722 transistors". Popular Electronics. Vol. 2 no. 4. New York: Ziff-Davis. April 1955. p. 8. CK722 advertisement
  5. ^ "How to Build Experimental Transistor Receivers". Popular Mechanics. Vol. 100 no. 4. Chicago: Popular Mechanics Co. October 1953. pp. 246–248. 
  6. ^ Garner, Lou (November 1957). "Transistorized Instrument Amplifier". Popular Mechanics. Vol. 108 no. 5. Chicago: Popular Mechanics Co. pp. 160–162. 
  7. ^ Schiffer, Michael Brian (1991). The Portable Radio in American Life. Tucson, AZ: The University of Arizona Press. pp. 161–165. ISBN 0816512841. 
  8. ^ Jack Ward's interview with Carl Todd

External links[edit]