This circuit turns off when switch S1 is opened. The circuit is from the 1989 Radio Electronics Experimenter edition; The triac must be controlled according to the load.
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...