This 1-transistor circuit for currents up to 50 mA was found in the August 1974 Radio Electronics magazine. The transformer is 50 to 200 mA.
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...