This circuit is from a 1968 publication. Here we have several types of resistive sensors with individual adjustments triggering a single SCR. Power depends on the type of sound device to be triggered.
We found this transistorized radio for the AM band in a Japanese publication from 1960. The...
This small source is suitable for low consumption equipment that uses batteries. The circuit is...
Found in a magazine 73 for radio amateurs, this circuit has two settings, one for the interval and the...