This circuit for VCR recording heads was found in the February 1990 issue of Radio Electronics magazine. The circuit is use do observe signal in an oscilloscope.
According to the author of this project, from a documentation on espionage from the 1980s, this...
This circuit suggested by Siemens can provide time intervals for triggering values that are given...
This circuit generates a good-intensity 1 kHz rectangular signal. The circuit is from Electronics Now...