This circuit was found in Philips documentation from 1965. No information was given about the transformer. Transistors are from the era.
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...