This ingenious circuit was found in a 1990s Popular Electronics. The oscillator is a 555 and the keyer uses an optocoupler in the configuration shown.
We found this amplifier circuit for inductive audio pickups in a documentation from the 70s. The...
The circuit is from Motorola's Linear Databook from 1990, but the configuration is current because...
This 6-transistor commercial radio with 6 V supply was found in a Japanese publication from the...