The use of a diac improves the performance of the two dimmers in the previous circuits. The circuit is from the same Radio Electronics magazine in an article that teaches how to use triacs.
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...