We found this circuit in the Linear Applications Handbook by National Semiconductor. It uses the LM3900, an operational transconductance amplifier as a base. Q1 can be a 2N2222 or similar.
This circuit generates rectangular TTL modulated signals. The transistor can be the BC548 and...
This circuit has 4 operating modes and was found in the 1995 Encyclopedia of Electronic Circuits...
This circuit was obtained in a 1965 American magazine translation. The photocell can be the type...