Electro-Voice 651-B is a Hi Fidelity semi-fixed frequency FM tuner designed for use in background music installations. It has three operating controls: a slide switch to turn the power on and off, a slide switch to disable the "Squelch®™ circuitry, and a slide switch to disable the AFC circuitry. Tuning is accomplished by means of a screwdriver at the right side of the tuner cabinet. The squelch circuitry eliminates sudden background noise that will appear if the broadcasting station goes off the air, while the AFC circuitry locks on the transmitter frequency to avoid drift.