This circuit was obtained in a Electronics World of 1968. The transistors can be equivalent as the BC558 for the PNP and the BD135 for the NPN powering lamps from 3 to 12 V according to the supply.
This circuit is from the 80's, using an integrated of the time. The circuit serves as a reference,...
This circuit was obtained from an American 80's documentation. The operational ones can be...
This logarithmic gain operating configuration was found in the June 1994 Electronics Now magazine. The...