The Telefunken EF804 is a special quality, low-noise pentode vacuum tube designed primarily for professional low-frequency (LF) audio applications, notably in high-fidelity microphone preamplifiers.
Professional Audio Use: The EF804 was specifically designed for the professional audio and recording industry. It was famously used in Neumann, Siemens, and Klangfilm preamps, including the highly regarded V72 and V76 models.
Low Noise and Hum: It features high plate strength, low hum, and very low noise characteristics, making it ideal for the initial stages of sensitive audio equipment like microphone preamps.
Special Quality (SQ) Versions: The standard EF804 has a "Special Quality" variant, the EF804S, which boasts a declared lifespan of over 10,000 hours, superior performance properties, and enhanced resistance to vibration and shock, originally designed for public broadcasting services.
Construction: This is a 9-pin miniature pentode (B9A Noval base) that is slightly larger than some other miniature tubes in its series.
Historical Significance: V72 preamplifiers equipped with the EF804 were notably used by producer George Martin during the recording of The Beatles' album Sgt. Pepper's Lonely Hearts Club Band.