8-ohm four-spring (4AB3C1B) reverb unit. 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®, Vibro-King®, Dual Professional, Super-Sonic™.
eBay