This crystal or galena radio was found in documentation from the 1990s. The earpiece must be a high impedance crystal or magnetic earpiece and D1 can be any germanium diode.
The resistor values depend on the desired gain and the full scale of the indicator instrument. The power...
The circuit in the figure combines a multivibrator with a comparator, so that the trip only occurs...
This circuit for measuring bridges was found in American documentation from the 60's. Transistors are...