This circuit, obtained from a 1965 magazine, can still be assembled using some modern equivalent components. The transistors may be BC558 and the transformer is obtained from a disused transistor radio.
We found this circuit in a 1965 publication by General Electric. The zener is 8.2 V x 1 W and the...
This circuit was obtained in an Electronic Engineering of the 90s. The operational amplifiers and...
This circuit is suggested by Texas Instruments in his Optoelectronics Sourcebook. The transistors...