Infrared modulated transmitter (CB7247E)

This simple Philips circuit from the 1960s can use any general-purpose transistor. The signal is modulated at 2.7 kHz.

High impedance preamplifier stage (CB4683E)
In the figure we have a high input impedance stage with a general purpose PNP transistor. An NPN transistor...
Colpitts Oscillator (CB6185E)
This circuit was obtained from an American 1980s documentation. The frequency depends on the...
Audio Oscillator CK722 (CB14744E)
The transistor can be a modern equivalent and the transformer is the type of output found on an...