This circuit using the CK722 among others came out in a September 1950 Radio Electronics. It was one of the first circuits of this type published with transistors that started to reach the market.
This stage was found in a 1964 Electronic Design. The transistors are of the time and the shape of...
The traditional circuit was taken from a French magazine Radio Plans that no longer exists but can...
This circuit, which is present in other points of this website, was found in a 90s Hands On...