This passive circuit was found in a 1980s documentation. The circuit serves to indicate the balance or balance between the channels of a stereo amplifier.
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...