Musical Fidelity Nu-Vista 800 integrated amplifier

Nuvistors—miniature, small-signal, vacuum tubes made of metal and ceramic—were introduced by RCA in 1959, at the dawn of the transistor revolution. RCA used them throughout the 1960s in its New Vista line of television sets, mostly in the tuner section. But by the early 1970s, solid-state devices had all but replaced tubes, nuvistors included (with a few notable exceptions). Ampex based the electronics of its well-regarded, late-'60s MR-70 open-reel tape deck on nuvistors, which were also used in microphone preamplifiers—in both cases for their very low noise and reputation for reliability and long life. For a time, Conrad-Johnson used them as well. While nuvistors may seem exotic today, they're hardly rare. On eBay you can find for sale hundreds if not thousands of used and new-old stock (NOS) nuvistors, as well as nuvistor sockets, without which the tubes are less easy to implement. (But they can be, and often are, hard-wired into a circuit.)