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 small triode sections held between two mica discs. The total anode dissipation was two Watts.
The blackened anodes are wide for good heat dissipation. Running the triodes at 10 mA improves the noise figure.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 48 mm tall.
Reference: Datasheet. Type 6BZ7 was first introduced in 1956.