This 1969 Mullar circuit appears elsewhere on this site. The circuit uses germanium diodes and the indicator is microammeter with zero in the center of the scale.
Found in a 1960 General Electric documentation, this crowbar circuit blows the fuse in case of...
This circuit was originally designed for testing crystals used in color televisions, but it works...
This bridge-biased transistor test circuit measures gain in the range 0 to 300. Circuit is from...