This circuit is intended for underwater communications. Of course, the critical point is the shielding to avoid water. The circuit is from an Electronic Hobbysts Handbook from the 90s.
This circuit turns a lamp on and off with alternate touches of a switch. Modern Darlingtons can be used....
This circuit with the CK722 was found in a Raytheon publication from the 60's. The relay is of the...
This circuit was found in Radio Electronics magazine from July 1960. The components used are...