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 obtained from a Hands-On Electronics, an American magazine from January 1987. The...
This receiver for listening to the TR-23 phone was manufactured in Japan in the 1960s. The circuit is...
This astable multivibrator with an operational one at the time was found in the National...