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.
This circuit can be used in tone-modulated optical remote controls or as an optical transmitter for...
This circuit sources a Constant current to a load. The current is determined by R2. In the...
This sound relay or Vox was found in 70s RCA documentation. SCRs can be common types today and...