This sensitive circuit for triggering relays was found in an old English publication. It works with alternating signals applied to its input. Transistors are general purpose types.
The varactor or varicap diode tunes the signal for listening to SSB signals on a common receiver. The...
This circuit was found in a Hands On Electronics from the 90s. It turns on an LED to indicate that...
This circuit was found in a 1960 transistor manual from Sylvania. The components are from that...