The 5X8 is a 9-pin miniature compound tube containing a medium-mu triode and a sharp-cutoff pentode within a single glass envelope. Engineered primarily for use as a combined local oscillator and mixer in high-frequency radio receivers and television tuners, it operates on a 4.7V/600mA controlled warm-up series heater. It was widely specified in late-1950s series-string chassis manufactured by RCA Victor, Zenith, Philco, and Sylvania. Available in NOS and tested used conditions.