Pedal based on the preamp of the 1955 and 1956 Fender Princeton 5F2 and 5E2, the “Narrow Panel”. As on the Princeton of those years, a Volume and a Tone. The Fender 5E2 saturates faster than the 5F2 which stays brighter at high volume, hence the “F to E” control which adjusts the saturation point from 5F2 to 5E2. And to brighten it all up a Bright switch.