We found this circuit in the 1964 RCA transistors manual. The transistors used are uncommon today, but they can be used equivalent. The circuit controls the operation of a heating element.
This circuit with LDR and neon lamp has its operating frequency given by the light. The circuit is from...
Found in American documentation from the 90s, this circuit can be used as a shield with the...
This tone recognizer circuit that relies on R5 and C1 was found in the December 1994 issue of...