Historical Background


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.  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.  Transistors which failed to meet the rigorous hearing aid performance requirements were not labeled 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.    Use these transistors as “mini-CK722s” – the performance is identical!








Germanium PNP Alloy
Hearing Aid Transistor

Vintage 1957

Use: Hobbyist/CK722


Your Transistor Museum™ CK78X Order Will Contain:

Two Tested Transistors

 (Style Shown Above)

Transistor Museum™ Classic Semiconductor Storage

And Display Envelope, with  Informational Insert

CK78X Historic

Semiconductor Fact Sheet

Use this Link to See the Complete CK78X FACT SHEET



$12 per Package (Two Transistors)

Add $3.00 Shipping/Handling within U.S.


For PayPal or Check Payment

Copyright © 2010 by Jack Ward.  All Rights Reserved.