“They are my favorite NOS I have tried.” Read
“… competent at best and not really anything special – in fact I would say this is a fairly unexceptional tube family with just a few high points… ” Read
Tube Maze
Guides and reviews of vacuum tubes and audio equipment
The Mullard CV4003 Box Plates is a fantastic tube and remains one of the clear leaders in its category. The level of detail it communicates during a musical performance is superb, providing a very smooth presentation that invites long, fatigue-free listening sessions. While it is highly capable, it is slightly less “communicative” than Mullard’s own 12AU7 Long Gray Plates, though this is expected given the higher price point of the long-plate version. When compared to the RCA Long Gray Plates, which is also known for smoothness, the Mullard definitely wins out, as the RCA variant can exhibit some sharp notes at the frequency extremes.
The CV4003 is the military-grade, high-reliability version of the 12AU7/ECC82. These “Box Plate” versions were produced at Mullard’s legendary Mitcham and Blackburn plants in the UK. Designed for rigorous military applications, they feature a ruggedized internal structure and box-shaped anodes, which contribute to their lower microphonics and exceptional longevity compared to standard consumer-grade tubes.
* Sonic Character: It is defined by a superb level of detail and an incredibly smooth tonal balance that makes it a favorite for high-end preamplifiers.
* Performance: The tube offers a more refined and consistent experience than the RCA alternative, avoiding harshness while maintaining a musical, “liquid” midrange.
* Value: While it is highly recommended, the tube is becoming increasingly expensive, often retailing around $50 per tube due to its status as a top-tier NOS (New Old Stock) favorite.
Final Verdict: HIGHLY RECOMMENDED as a premier military-grade 12AU7 that delivers a detailed, smooth, and world-class listening experience.