This circuit was found in documentation from the 1980s. It is powered by the audio signal that must be cut. Transformers are the critical components and transistors are 2N2222.
This circuit was published in a January 1971 issue of Radio Electronics to check television...
Found in Popular Electronics from the 90's, this tuned to infrared modulated receiver uses a PLL....
This 1967 General Electric circuit makes use of an array of 3 (integrated) transistors for an...