This circuit is from American documentation from 1970. It can be designed with a BC558 and for the operational, we can use equivalents. The FET can be the BF245.
November 2016 - Already available from Mouser Electronics on Texas Instruments' new DS280BR820...
This circuit generates a pulsed tone whose frequency depends on C2 and whose flashing depends on...
The presented circuit is suggested by National Semicondictor in its 1994 Linear Applications...