This circuit provides reverse power polarity protection using a power MOSFET and a diode. The MOSFET must be current in accordance with the current of the protected circuit.
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...