Microammeter (T465E)

Found in a 1948 MIT documentation, this circuit uses a 0 to 100 uA microammeter as an indicator. The power supply is 150 V.

Digitally controlled audio switch (CB12748E)
This circuit can serve as a basis for a digital mixer or simply for a noiseless switch of audio...
Microphone mixer (CB7988E)
This traditional mixer configuration with a high input impedance was found in a 90’s Popular...
1-transistor radio (CB20247E)
This medium wave radio works with any general purpose NPN transistor. The diode must be made of...