Operating in the range of 3 to 100 MHz, this circuit was found in documentation from the 70s. Observe the coil. The field effect transistor is a component of the era.
This circuit, from Texas Instruments documentation, fires a relay when light strikes the...
This circuit was found in documentation from the 1980s. The circuit can be implemented with other...
This circuit is from an 1977 American publication. The coil consists of 30 + 70 turns of 28 AWG...