This variable filter that lets frequencies from 500 Hz to 1500 Hz pass through was found in a Popular Electronics from the 90's. The operational amplifiers are the 741.
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...