This circuit was found in a 90s Electronic Design. The circuit directly controls a triac that is loaded with a heating element. The triac depends on the power on the load.
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...