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.
This filter, from an audio publication from 1977, passes the frequency range corresponding to the...
In the figure we have three voltage doubler configurations that can be used in high and low...
This circuit was found in Motorola documentation from 1966. The lamps are according to power and...