This circuit allows the detection of RF signals using the lowest range of direct currents of a common multimeter. Equivalent diodes such as 1N34 can be used. The circuit is assembled in a ballpoint tube.
The circuit is from a Radio Electronics magazine from October 1987. The Triac must be equipped with a...
I found tis circuit in na old documentation from 1958. The circuit uses germanium transistor...
Today we have more compact solutions. This is from a Radio Electronics magazine from October 1990....