This is the Antique Astra Lark Germanium diode Crystal Radio. The Astra Lark PT-8, was made by Dachi Electronics in the 1950's in Japan.
This crystal radio is operated by a NEC SD46 germanium diode and has a high "Q" provides a much clearer, and louder radio reception than that of the old type regular coil crystal sets. The variable capacitor is a Poly Film Variable Tuning Capacitor that is larger in size, compared to the Poly Film Variable Tuning Capacitors that are used today. The Astra Lark PT-8, can use a telescopic antenna that opens up to 20 1/2 inches; or it was a wire that can connect to a outdoor long antenna, to receive radio stations that are farther away. I received 3 different radio stations, using a long antenna; and they all sounded loud and were very clear. There is also a small resistor between the two earplug wire terminals. There is no ground wire connection used on this crystal radio.