Float the phrase “tube reverb” and most players are likely to conjure up an image of one of Fender’s creations, whether it’s a blackface amp like the Deluxe Reverb or Twin Reverb, or this stand-alone 1961 Reverb Unit. This unassuming brown box was in fact where reverb was born, as far as the Fullerton company was concerned, and it remains, for many players, the zenith of that wet, atmospheric sound.
Although Fender was late to the game—Ampeg, Gibson, Danelectro, and others had already introduced the effect—the Fullerton, California, company would set the standard for tube-driven spring reverb in ’61, when it debuted the humbly named Reverb Unit, which introduced a sound that would be difficult to accurately replicate in the post-preamp reverb stages subsequently included in most guitar amplifiers.
The Fender Reverb Unit also offers more controls than most amp-based reverb circuits, with knobs for Dwell (depth), Mixer (reverb/dry blend), and Tone (brightness of the effected signal). It also has a deep, lush, watery sound thanks to an uncompromising tube-driven circuit. Circuit-wise, the Reverb Unit, which is designated Model 6G15, is essentially a small amplifier in and of itself. Instead of driving a speaker, however, it drives one end of a set of springs in the “tank,” with a transducer at the other end of the springs to pick up the delayed signal, which is then amplified and blended into the dry signal. As such, the Reverb Unit contains 12AT7 and 7025 preamp tubes, and a 6K6GT output tube (a slightly weaker variant of the 6V6GT, which is often used in reissue units). It also has both power and output transformers. All in all, enough circuitry and components to build a small, single-ended amp, not unlike a Champ.
As a result, this became the sound of surf guitar and a must-have effect for guitarists—and indeed vocalists—in several other genres. When used with guitar, it’s designed to be placed in front of the amplifier, which is to say, to be connected between your guitar and your amp’s input as you would most traditional effects pedals. As such, Reverb Units function best when plugged into vintage-style, low-gain amplifiers. Although they can be used in the effects loops of some amps, they don’t tend to perform their best in such setups.
A few minutes spent playing with a great vintage unit quickly reveals what a wonder this effect must have been in its day. When set just right, the Reverb Unit adds an ethereal dimension to your guitar tone, and takes you on a sonic trip rarely bettered by more dramatic delay or modulation effects. It’s still a major classic—and little wonder. Surf supremo Dick Dale was one of the first major proponents of Fender’s Reverb Unit, and soon after its release every other surfer worth their salt had to have one—as did every other pop, jazz, and rock ’n’ roll guitarist on the block. Over the years, the Reverb Unit’s liquidy sproing has also graced the playing of Neil Young, J. Mascis of Dinosaur Jr., and Stone Gossard of Pearl Jam, among many others.
> Fully tube-driven
> Long Accutronics spring tank
> Controls for Dwell, Mixer, and Tone
> Brown Tolex covering with wheat grille cloth
> Tubes: 12AT7, 7025, 6K6GT