Found in an Australian documentation from 1991, this circuit was sold in a kit at the time. It is a small FM transmitter with a very common configuration, also found in other projects on this site.
The circuit shown is from the Texas Instruments optoelectronics manual, applying to low power...
This circuit was found in a 1968 General Electric documentation. It has an input impedance of 2 M ohms...
This filter that rejects a frequency range determined by the double-T was found in the August 1993...