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.
In the figure we have an amplifier configuration found in an 80's documentation. The power supply is...
Suggested by a Philips documentation from 1970, this circuit uses period components, operating at 50...
This circuit was found in a Radio Electronics from April 1990. The circuit has 5 equalization...