Originally designed for WWV (Standard Time Station) signals, it lets 1 kHz tones pass by rejecting the 440 and 600 Hz tones emitted by the station. The circuit is from a 1964 Electronic Design.
This circuit was found in a Delco 1965 publication. Transistors may be current equivalents according...
This circuit makes an incandescent lamp blink in order to vary its brightness with a candle...
This configuration was found in a 1970s American magazine. The circuit uses both CMOS logic and...