This circuit was found in a 1964 Electronic Design. The components are of the time, and modern equivalents can be used. Note the multi-emitter transistor.
When the sensor connected to points A and B is activated, removing the ground from the base of Q1...
This oscillator was found in the 1994 National Instruments Linear Applications Handbook. The...
With the circuit shown in the figure, the frequency of a 5 MHz oscillator controlled by crystal can...