This high-Q low-pass filter was found in the October 1990 issue of Radio Electronics magazine. The frequency depends on the capacitors used and is on the order of a few tens of hertz.
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...