Filament source (T398E)

Despite being transistorized, this is a constant current source circuit for 1 V valve filaments such as the 1H4 tube.

Filter selection circuit with PIN diode (CB20933E)
Found in Popular Electronics from the 1980s, this circuit is intended for switching filters with...
Stereo FM Transmitter with the BA1404 (CB12595E)
The BA1404 integrated circuit (not very easy to obtain) consists of a complete stereo FM...
Few Component FM Transmitter (CB10004E)
This transmitter uses an electret microphone and has a few tens of meters in range. The coil L1 is...