This circuit was found in an Electronic Design from 1964. The components are from that time and can be replaced by equivalents. The modulation ranges from 0.25 to 0.75 of the 20 kHz pulses.
This circuit is from a publication from the 70s, but it can be assembled with any diac and a Triac...
This circuit was obtained in a 1983 publication. It is a 1-transistor voltmeter, capable of...
This circuit from Radio Electronics magazine, March 1994 edition uses two LM388 bridged, providing a 4...