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CK722 projects

Raytheon introduced its famous experimenter-geared low-cost transistor CK722  in 1953 and it was still manufactured through late 60's. Soon after, Raytheon made available the CK721, a somewhat lower noise and higher gain of Ck722, actually coming from the same batch and sorted as a "better" transistor. The cut off frequency of these transistors were rather low - 600KHz for CK722, 800 KHz for the CK721 although some units would oscillate at 1Mhz tops.  So, a few years later, Raytheon introduced the CK768 with the whopping alfa cut off frequency of 3.5MHz, allowing hobbyists experimentation with short wave receivers and transmitters. Commercial RF transistors were already available at the time but very expensive for hobbyists: 2N112/CK761, 2N113/CK762, 2N114/CK762 and the like. These can be found in transistor radios Raytheon manufactured in the 50's. 
There are great websites on the subject with detailed history, and loads of pictures and applications of these early Raytheon transistors, my preferred one is semiconductormuseum.com/CK722  created by Jack Ward who was once interviewed on the subject in the March 2003 issue of the prestigious IEEE Spectrum Magazine.
You can download here the excellent book Raytheon Transistor Applications which is a collection of over 50 transistor projects using the CK722 and CK721. Many of these projects appeared in magazines such as Radio Electronics and Radio and Television News of the time. 

Highly compatible CK722 substitutes include types: CK721, 2N63, 2N64, 2N130, 2N131,

Project Schematics

Type CK721 and CK722 transistors may be purchased from the Transistor Museum Store.