The Fender Reverb Unit (6G15) was a tube, spring reverb-equipped effects unit made by Fender. The Reverb Unit was originally introduced in 1961. It was discontinued in 1966 and was replaced by a solid-state model, the FR1000. The unit features three controls: Dwell, Mixer and Tone and includes a 12AT7 tube as a preamplifier; a 6K6 tube as the reverb driver; and a 12AX7 as the reverb recovery tube. The rectifier is a diode-type solid state unit. The circuit board, like Fender’s brown, “blackface” and “silverface” amplifiers is an eyelet board and the unit its completely hand wired. Physically the unit looks like a small amplifier head and since the early 1960s the unit has become synonymous with surf music, The tube reverb was reintroduced in 1976 with a silver control panel (“Silverface”). It was discontinued in 1978.