This circuit is from a Hands-On Electronics from the 90s. The integrated amplifiers used are well known. The range is a few tens of meters depending on the resistance of the cables.
This circuit was found in an 80's Radio Electronics. The circuit makes use of common components and...
This circuit was found in a 1968 RCA documentation. The circuit can be designed with operational...
This circuit for timing small loads was found in a 1964 General Electric documentation....