This triac circuit was taken from an article in the July 1970 Radio Electronics magazine. Note the snubber formed by R5 and C3 for controlling inductive loads.
This filter has a cutoff frequency of 0.026 Hz given by R and C. These components can be...
In the figure we have a way of receiving ultrasonic signals of a single frequency using a PLL 567....
Using integrated circuits from the time, we found this audio compressor in an English publication from...