Ampeg's Portaflex or "flip top" series of amplifiers debuted in 1960. Combo amplifiers were convenient because of their portability, but the space was limited inside the cabinet and the tubes often overheated due to the lack of cooling. Piggyback amplifiers (separate amplifier heads and speaker cabinets) solved this problem, but the portability was gone. The new Portaflex design combined elements from both of these designs to solve these problems. In the Portaflex, the amplifier chassis was mounted on a removable panel that acted as the top of the cabinet. When the player was using the amplifier, the chassis locked onto the cabinet like a Piggback unit and allowed the tubes and transformers to properly cool. For storage or transport, the chassis was unlocked and flipped over to sit inside the cabinet. When the chassis was stored, it looked like a regular combo amp or speaker cabinet. The chassis connected to the cabinet through a single cable, and nearly all Portaflex amplifiers were sold with the optional four-wheel dolly. Part of the chassis included a light up lucite Ampeg name plate that would illuminate when the amplifier was in use. Ampeg also allowed owners to personalize the name plate with their name to let others now whose amp it was!
The Portaflex design was a constant model in the Ampeg line between 1960 and 1980, but each model underwent several revisions that were often noted by a letter suffix such as "B", "C", or "Y". Please note that the amplifiers themselves often did not include the suffix letter. For instance, the B-15N with a solid-state rectifier is still called a B-15N although according to Ampeg's service records, it is referred to as the B-15NB.