Found in a 1970s documentation, this mini-organ toy circuit makes use of an integrated circuit from that time. This component is difficult to obtain today.
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...