Quad Cities | Quad City Symphony Orchestra | Quad City Flames | Morris "Quad" | ATV Quad Power Racing 2 | Quad City Steamwheelers | Quad City Knock | Quad | quad | Milwaukee-Downer "Quad" |
It was the standard output tube in the classic Quad II (1952, a version of which is still being manufactured today) and in the LEAK Type 15 (1945) and TL/12 (1948), both among the earliest British hi-fi amplifiers.