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 circuit identifies the polarity of DC signals and if the signal is AC. The circuit is from...
Found in American documentation from the 1990s, this circuit generates signals in the 350 to 500...
This circuit was obtained from HAM Radio magazine in an 80's issue. The FETs are types of the time...