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.
Today we have more compact solutions. This is from a Radio Electronics magazine from October 1990....
This filter was found in Texas Instruments documentation from the 1980s. The circuit uses a common...
16 commercial test circuit for tubes and transistors appeared in Radio Electronics magazine in...