This circuit identifies the polarity of DC signals and if the signal is AC. The circuit is from 1969 US EDN documentation. Operational may be equivalent.
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...