Found in an 1868 Mullard documentation this circuit has a dynamic range of 10 Hz to 25,000 Hz. Modern equivalent transistors can be used.
This circuit was found in an old publication from 1989 but can still be assembled today with BD135...
We found this circuit in a 1987 documentation. Its purpose is to turn on a garage light using the...
In the figure we have a simple logic level indicator for TTL circuits or powered by 5 V....