The 6BZ7 is a double amplifier triode designed for cascode operation is VHF television tuners. The standard European valve for this task was the PCC84. The 4BZ7 was electrically the same but the heater rating was 600 mA at 4.2 Volts for series heater chains.
The RCA name and logo printed on the glass.
The small twin triode sections with a bright Z shaped screen between.
The thin glass tube envelope is 21 mm in diameter and, excluding the B9A base pins, is 48 mm tall.
Reference: Data-sheet. Type 6BZ7 was first introduced in 1956.