Found in a 303 Circuits from the 90's this circuit can use the lowest current range of a common multimeter. The circuit can measure currents as low as 100 pA.
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...