1960s tube spring Reverb Unit.  Super clean Multivox Premier 90 Reverb Unit, functions and looks like new.  Very unique-sounding box with plenty of character.  Drive it hard for a nice dirty sound or back off for a nice warm tube reverb.  Adjusts to a nice wet surf 'verb.  Why pay a lot for a Fender. Serial number 116151.  Made in the USA. 
All original.