Recommended for automotive applications, this circuit was found in an April 1982 Radio Electronics magazine. The transistor supports equivalents. Sensitivity adjustment is made by R1.
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...