This circuit with zener diodes was found in documentation from the 90s. The zener diodes determine the lighting point of the LEDs. The circuit is for 12 V automotive batteries.
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...