5BK7A

Medium-Mu Dual Triode Amplifier Tube, identical in electrical characteristics to the 6BK7B architecture but equipped with a 4.7V heater filament. It is engineered specifically for series-string heater circuit configurations in low-noise VHF cascode RF television tuner stages, housed in a standard 9-pin miniature glass envelope (Noval, T-6.5 bulb).