Laurens Hammond of Illinois popularised the use of artificial reverberation devices through his church organs in the 1940’s and 1950’s. The early (pre-B-3 ) Hammond organs were sold to churches on the principle that organ music is greatly enhanced by reverberation, but the minister's speech in the church is hampered by reverberation. Therefore, churches were designed to be acoustically dead, and the Hammond organ had to have its own artificial reverberation. Reverberation made its debut in the Fender line as a separate item, using a spring unit bought from Hammond , in 1961. It was first incorporated in a Fender amplifier with the Vibroverb of 1963 and then spread widely throughout the amp line, just as vibrato/tremolo had before it.
The main components used to produce the spring reverb effect are:
• Input and Output Transducers - Each transducer consists of a coil centred around a magnetic lamination and small cylindrical magnets centred in the air gap of the lamination.
• Transmission Springs -These components are mounted on an inner aluminum channel, which is connected by four small support springs to an outer steel chassis (or channel).
An electrical signal applied to the input transducer coil generates an alternating magnetic field which moves the transducer magnets. The magnets are mechanically coupled to transmission springs. The signal is reflected back and forth through the transmission springs with an amount of delay determined by each spring's diameter, wire gauge and length. The moving magnets of the output transducer generate an alternating magnetic field which induces an electrical signal in the output transducer coil.
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, Mix and Tone and is run by two pre-amp tubes and a power tube. Physically the unit looks like a small amplifier head and since the early '60s the unit has become synonymous with surf music.
This unit is in perfect working condition and adds a great sound to any guitar/amp.