This very complex circuit in terms of the number of transistors was found in Radio Electronics from March 1966. The circuit is for low impedance headphones. The transistors are from the time.
The recommended distance between the emitter and the phototransistor is 10 mm for this...
The input and output frequencies of this circuit depend on the coils and capacitors of the tuned...
This circuit was obtained in a 1991 publication. What it does is to amplify a signal with unit...