This circuit is from an American 1967 documentation and can be implemented with modern equivalent transistors. The circuit serves as a Q multiplier.
This circuit was found in Philips documentation from 1967. The phototransistor is from that time,...
We found this third-order Butterworth asymmetric filter in an old manufacturer documentation. The...
We found this circuit in a publication for radio amateurs of 1976. The operational amplifier is a...