This circuit was found in the May 1990 Radio Electronics magazine. The timings depend on the capacitors and the supply voltage depends on the relay used.
This circuit was found in 1980s American documentation. The transducer is a piezoelectric capsule and the...
This circuit from the 80s uses an integrated circuit from the time. The CI is difficult to find...
This receiver, which, depending on the coil, can receive medium or short waves, was found in a...