This Mullard circuit was found in a 1969 documentation. It uses complementary transistors on the output and does not need a transformer. The bandwidth goes from 100 to 20 000 Hz.
This circuit was found in an 80's Electronic Engineering. The circuit uses a multivibrator with...
This circuit was found in a 1960s book of projects by Gernsbak. The circuit uses germanium...
This circuit was found in an American documentation from the 80's. The components are from that...