This circuit is based on the TDA3810N. We found it in the March 1992 issue of Radio Electronics magazine. The circuit consists of an audio processor capable of working with two audio channels.
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...