In 1956, Ampeg introduced their Guitaramp/Accordiamp Series, but many of these amps were still built one at a time as opposed to on a production line. The problem with amps produced in the late 1950s is that around this time Ampeg was using the same chassis for many different amps, and it was difficult to decipher model numbers as they weren't often listed on the amp. Model numbers were listed by the type of amp. If it was a Bassamp, the series were numbered 800 or 8000, Accordiamps used 400 or 7000 numbers, and Guitaramps used 6000. In 1958, the model numbers were converted to all three-digits (the 6000 changed to 600 and the 7000 changed to 700). Tremolo was only available in the guitar and accordion amps and Bassamps had deeper cabinets with a slanted control panel. In 1956, the logo changed and the "p" in Ampeg now went through the line underneath the logo. The Dolphin, Zephyr, and Continental amps were all voiced for guitars and the Jupiter, Rhapsody, and New Yorker are all identical respectively, except they are voiced for accordions.
Ampeg produced other models without much information on them including the 518 Dolphin Special, the Model 435 SN, the Model 635-S Zephyr, the Model 720-SN Jupiter II, and the 625-SN Constellation. Most of these amps were submodels of more popular models and often only have minor differences or were made at a different time period.