In this receiver the is formed by 80 turns of wire 28 or close in a ferrite rod. The handset is low impedance and powered by a standard battery.
This is an old test circuit for integrated TTL counters, feeding a Nixie tube, common at the time....
This old oscillator using germanium transistors has a high impedance headphone as inductor to...
This preamp with several inputs using germanium transistors from the time was found in Japanese...