This variable frequency (VFO) oscillator was found in a Japanese publication of 1962. Coil details (in Japanese, but can be deduced) are next to the diagram covering the 3.5 MHz band.
One 40108 Schmitt inverter or one 4093 gate can be used as a half monostable to be triggered by...
This signal generator found in Japanese documentation of 1973 uses an unusual integrated circuit...
This is the basic configuration of an operational amplifier as a current regulator. We found it in...