Fender 4-Spring 8 Ohm Spring Reverb Unit (4AB3C1B) Direct replacement reverb units used in Fender amplifiers with spring reverb 8 ohm replacement 4-spring (4AB3C1B) reverb unit with RCA style input and output jacks Long decay design (2.75-4.0 seconds). Mounts horizontally to floor of cabinet with open side down Used in Prosonic, Showman 50, '94 Twin, Custom Vibrolux Reverb, Custom Vibrasonic, Pro Tube Series, '63 Vibroverb, '65 Twin Reverb, '65 Deluxe Reverb, '65 Super Reverb, '65 Twin Custom Also used in Vibro-King, Dual Professional, Super-Sonic Series, '64 Vibroverb, Princeton Recording Amp, and '65 Princeton Reverb amplifiers manufactured from 1991-Present