Found in an American publication of 1968, this circuit makes use of a pilot light of the time. It can be replaced with LED with appropriate series resistor. Transistors may be modern equivalents.
This amplifier was found in a Maxim documentation from the 90's. The circuit is an inverter type with...
This interesting circuit was found in a 1968 documentation. The transistor can be a...
This circuit suggested by Motorola can be used as LED high frequency modulator. One possible...