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.
In this circuit the CA3140, an operational amplifier, is used as a comparator with the zener diode...
This linear LED scale circuit was found in the February 1992 issue of Radio Electronics magazine. Note...
This amplifier stage without an output transformer was found in Radio Electronics magazine from...