This circuit is for 12 V batteries but can be used with batteries of other voltages by changing the zener diode. The trigger point is adjusted by R1. The operating system accepts equivalents.
This circuit was found in a 1977 Radio Handbook. The ports used are CMOS like 4001 and the...
I found this Vox circuit or acoustic receiver as it was originally called, in a 1973 publication. The...
Found in RCA documentation from the 90s, this bass and treble control uses an operational...