The UVTRON tube is an ultraviolet radiation sensor. In this circuit from Radio Electronics from April 1990 we have a flame detector.
This oscillator has its frequency controlled by crystal and its frequency can be between 100 kHz...
This small crystal microphone transmitter was indicated in an 80s spy book. The range depends on...
The circuit shown is from the 1994 Linear Applications Handbook by National Semiconductor. The...