This  wikipedia page Dumble amplifiers are extremely influental to musicians amp buildersmanufacturers collectors etc Their value is in their sound  As said on the wiki page many amp manufacturers are building amps based on mr Dumbles designThe design is alive and available and influentalThe man himself is a living legendIn many ways one could descripe Dumble amps superior to many people they are just ask Larry Carlton or robben Ford or Carlos Santanafamous musicians if you dont knowAll the business either directly from the original amps or services from dumble or in some way related to his work similar products or any sale mentioning his name is worth a considerable ammount of money