Found in a 1960s RCA manual, this circuit uses components from the era. For the indicated circuit R1 is 28ohm and R2 is 1 k.
We found this circuit in a Hands-On Electroncs from the 90s. The circuit uses an LED indicator. Diodes...
This circuit was obtained in a 1973 national publication, translated from an English publication of the...
We found this circuit in a 1983 English magazine, but it can be easily assembled with the BC548...