By 1952, Raytheon was making thousands of the its new alloy junction transistor every week.  These were tested for a variety of parameters, such as power gain and noise factor.  The primary market for these transistors was for hearing aids, which consumed an average of 70,000 Raytheon transistors a month in 1954.  Only about 1/2 of the early Raytheon transistors which were tested to be functional performed well enough to be used in hearing aids; this market required relatively high gain and low noise factors in order for the resultant hearing aids to meet acceptable quality levels. This meant that there were literally thousands of functional Raytheon junction transistors available for the general use (not hearing aids). These transistors were further tested and sorted into different performance levels, with the resultant transistors being assigned model numbers depending on performance.  Models CK718, CK721 and CK722 were the initial unit types identified, with the CK718 meeting strict hearing aid requirements, the CK721 providing moderate gain and noise factor -  the CK722 was the model number assigned to all the remaining functional units which met the minimum acceptable gain requirements (minimum power gain of 30db and noise factor of 22db).


See the original CK722 spec sheet.  






The original CK721 and CK722 was announced to the general public in the February, 1953 edition of Radio Electronics magazine.  The CK721 was marketed as a high gain type.  During the manufacturing process, functional units (shown in the top row of this figure) were sorted according to performance. Low noise/high gain types were labeled CK718 and supplied to hearing aid manufacturers.  The CK722 label was reserved for the lowest performing units (which still met advertised specs) and were destined for the general purpose “hobbyist” market.



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