The 5BT8 is a 9-pin miniature compound tube containing a medium-mu triode and a sharp-cutoff pentode in a single envelope. Designed for VHF oscillator-mixer, sound IF, and video amplifier service in television receivers and radio front-ends, it operates on a 4.7V/600mA series heater with controlled warm-up time. It was commonly featured in late-1950s series-string chassis produced by manufacturers such as RCA Victor, Zenith, Philco, and Admiral. Available in NOS and tested used conditions.