This continuity test was found in a 90s Electronic Engineering. Transistors are types of general use of the time with equivalents such as BC548 and BC558.
We found this circuit in an 80's Radio Electronics. It can still be easily assembled as the used...
This preamplifier for the phonographic capsule was obtained in an Argentine publication from 1973....
The circuit shown in the figure below is suggested by ON Semiconductor (www.onsemi.com), based on...