Found in old documentation, this circuit uses a double gate MOSFET. The operating frequencies depend on the coil, and the indicator is a microammeter.
This very simple 1-transistor oscillator is from Raytheon's transistor manual of the 60s. The...
This circuit is from a 1957 Raytheon transistor manual. The diode can be of general-purpose...
We have in the figure an ultra-simple alarm found in a 1981 publication. As the author indicates, it is...