The 4BN6 is a specialized 7-pin miniature gated-beam tube designed as a combined limiter, discriminator, and audio driver for FM radio receivers and television sound IF circuits. Featuring a 4.2V heater rated at 450mA for series-filament strings, its unique internal electron-gun construction allows high-efficiency FM detection with exceptional noise limiting without requiring complex ratio detector transformers. It was used in FM tuner sections and TV audio stages by manufacturers such as Zenith, Motorola, and General Electric. Available in new old stock (NOS) and tested used conditions.