The amp I've got is a model 59A (see pic). The labling on the cabinet back, and on the owner's manual, refer to model A-690, which seems to me to be a designation for this Ambassador component configuration--amp 59A, tuner 59T, 4-way speakers with 12-in woofers, and Dual 1009 record changer (plus one of several cabinet styles).
I just make a point of this because it might help you find info on your amp as you troubleshoot.