Telefunken EF-800
A tube that keeps turning up in the parts lists of microphones people actually care about.
Overview
The clearest documentation comes from the Miktek CV4, a large-diaphragm multi-pattern tube condenser that shipped with an "original NOS Telefunken EF800 tube" at the heart of its signal path. According to the manufacturer's own product copy, the CV4 pairs that NOS EF800 with a custom AMI BT4 transformer to chase "a classic sound you'd expect from the earliest vintage tube microphones" - the warm, tight, big bottom end and sweet, airy top that the copy insists is "indistinguishable from the most expensive mics in its class." That is advertising copy, not an independent measurement, and collectors should read it that way. The choice of tube is still interesting. A designer building a premium microphone in the 2010s reached for a stock of original Telefunken EF800s instead of a current-production alternative, and that is the kind of decision made by people who have listened to the options.
The period press noticed the tube. Electronic Musician (2010) covered the CV4 in a studio-gear roundup and singled out the "NOS Telefunken EF800 tube" alongside the transformer as the defining elements of its voicing. It described the mic as equally at home on vocals, piano, and drum overheads. Pro Audio Review (January 2010, p.41) went further in its own writeup of the CV4. It listed the NOS EF800 tube among the "features critical to the sound" and confirmed the mic's 20 Hz to 20 kHz range and 130 dB SPL handling. Those figures describe the microphone, not the tube, but they do show the EF800 in a full-range, high-headroom design.
The archive can't tell you much else. There is no confirmed production window for the EF-800, no original price, no pinout or heater specification on file, and no independent bench data. Owners and collectors hunting for one should be suspicious of any listing that quotes hard electrical figures until a manufacturer datasheet surfaces. The EF-800's reputation rests on its use in finished products, not on published curves.
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