TRANSISTOR MUSEUM™

Historic Transistor Photo Gallery   

 

Transistor Size (1/8”W X 1/8”H)

 

Date Code 746 on Back (1957 Week 46)

 

RAYTHEON CK78X

 

TYPE

Germanium PNP Alloy Junction

 

USAGE

Hearing Aids

Hobbyist/CK722   

 

DATE INTRODUCED

1955

 

CASE STYLES

Silver or Blue Painted Metal

 

 AVAILABILITY

Limited (Hearing Aid Usage)

HISTORIC NOTES

Raytheon was the early leader in the manufacture of germanium transistors, with the largest quantities destined for use in hearing aids.  These first Raytheon hearing aid transistors (labeled as CK718) were crudely made devices using a black epoxy case.  The epoxy was not an effective seal against moisture penetration, which eventually degraded the performance of the transistors.  Raytheon made rapid improvements to their transistor manufacturing processes, and introduced a much more robust, metal cased hearing aid transistor type in 1955, the CK78X series.  Each transistor was tested and, based on specific performance characteristics such as gain, noise and leakage, the resultant functioning transistors were labeled with the corresponding model number.  As shown above, the blue painted unit was selected and marked as a CK782 and found its way into a hearing aid.  Transistors which failed to meet the rigorous hearing aid performance requirements were left unpainted (top photo) and were used by Raytheon to produce the CK722/721 hobbyist line of devices.  These unpainted CK78X transistors were encapsulated inside the larger metal case of the CK722/721 type and were sold by the thousands to electronics hobbyists, eager to use these unique devices in their next radio or audio amplifier project.  

 

 

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