This is the crystal earpiece which is supplied in the kit with the ear tube removed to allow flat packing. Some technical measurements are shown for the electronics engineers. These units are properly tested before packing to ensure that they are working, as the current supply chain has problems with poor electrical bonding to the aluminium diaphragm. (See problems with dead and intermittent crystal earphones)
The combination of the 470pF capacitor, LT44 transformer, and this type of earphone produces good sensitivity and a high input impedance to the combined circuit due to a fortunate resonance with the inductances in the transformer.
There is more discussion to be had on the older crystal earpieces which look very similar, made from the 1960's until about the mid 1980's. They tended to be highly variable in their properties. The modern types suffer from much less variation when you are supplied with a working tested one.
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