We found this circuit in a 1969 General Electric documentation. The circuit uses transistors of the time and the diodes in the dotted board must be mounted on the output transistor heatsinks.
This UAA170 application circuit was taken from Siemens' own integrated circuits manual from 1976....
We found this circuit in the 1960 Mullard transistor reference manual. The phototransistor can be a...
Found in National Semionductor documentation this circuit combines a tone control with an...