Found in a 1991 PE Hobbyst Handbook, this circuit activates an oscillator that deactivates at the end of the programmed time. Transistors are commonly used.
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...