26-06-2023, 06:30 PM
(This post was last modified: 26-06-2023, 06:40 PM by Mike Watterson.)
So for exhibition rather than use and some (most) may be poorer than an 1N60, coil and ceramic disc as earpiece/capacitor with 10K Ohm.
They usually drove 2 x 2K earphones in series and needed a big aerial and earth. The galena crystals may have deteriorated.
Any 1899 to 1930s crystal set is really for display, though some may work. They used moving iron high impedance coils (2K). The crystal earpieces in 1940s to 1970s used a piece of crystal and foil diaphragm and were originally for hearing aids in the 1940s but used for covert radios. Like old crystal pickups they go off with damp, so the ones currently sold have a ceramic disc bonded to brass disc (as in beepers) and are about 2nF capacitance. A 10nF beeper disc seems to be upper limit. A beeper disk in small chamber with hole as an earpiece works well with about 10K load on the 1N60 diode (superior to OA81 or OA47). Adjust aerial coupling to coil for volume.
Various crystals and also oxidised copper discs used with an adjustable wire (the Cat's Whisker) were used as detectors. You can make copper oxide rectifiers with even a lighter. Old style tempered razor blades can work as can rusty bolts on a transmitter mast and then you get second harmonic!
Edit: The Wikipedia article describes the older crystal earpiece, the ones sold now are all the inferior ceramic disc like in a beeper.
They usually drove 2 x 2K earphones in series and needed a big aerial and earth. The galena crystals may have deteriorated.
Any 1899 to 1930s crystal set is really for display, though some may work. They used moving iron high impedance coils (2K). The crystal earpieces in 1940s to 1970s used a piece of crystal and foil diaphragm and were originally for hearing aids in the 1940s but used for covert radios. Like old crystal pickups they go off with damp, so the ones currently sold have a ceramic disc bonded to brass disc (as in beepers) and are about 2nF capacitance. A 10nF beeper disc seems to be upper limit. A beeper disk in small chamber with hole as an earpiece works well with about 10K load on the 1N60 diode (superior to OA81 or OA47). Adjust aerial coupling to coil for volume.
Various crystals and also oxidised copper discs used with an adjustable wire (the Cat's Whisker) were used as detectors. You can make copper oxide rectifiers with even a lighter. Old style tempered razor blades can work as can rusty bolts on a transmitter mast and then you get second harmonic!
Edit: The Wikipedia article describes the older crystal earpiece, the ones sold now are all the inferior ceramic disc like in a beeper.
