This circuit is from a 1968 documentation. It makes use of thermistors (NTC) to indicate overheating of charged batteries. Modern equivalent components can be used.
Found in a 90s Popular Electronics, this circuit provides a current of 3 to 5 A depending on the...
We found this circuit in the 1964 RCA transistors manual. The sensor may be a common LDR and the...
This circuit has tone control, and its power depends on the supply voltage. The circuit is from...