In 1961 the Magnatone amplifiers were rebranded Magnatone by Estey when Magna Electronics became Estey Electronics (see "History" for more about this change). In keeping with rebrands, model names and appearances changed, but circuits, for the most part, remained the same. Reverb was added to some units.
The redesign was pushed to meet the 1961 NAMM show, where Stan Green and the new Estey execs wanted to roll out the new amps, the ORCOA by Estey reed organs, and the Estey electric organs all at once. The Custom 200 Series names were bumped from the 200's to 400's, and all the small non-200's were brought into the 400's as well (This was part of a bigger plan at Estey. Existing organ lines, as well as some new lines were being aligned in series groups 200, 300, 500, 900).
The smallest amp was the 5 watt 410 and the largest was the stereo/stereo Vibrato 480, and in between were the 413, 425, 440, 450, and 460 models. Estey also operated as an OEM (orginal design manufacturer) for several accordion manufacturers and a few of these models were built and sold under names like PANameric, Noble, and Titano. While these amplifiers weren't sold under the Magnatone name after 1963, they were under these other brands for a few more years.
Jack Bartholomew was first hired at Magna in 1956, and was promoted to Chief Design Engineer to 1961. Ralph Greer was an engineer hired about that time as well. Fred Krueger was also an important engineer at Estey in those days, and the use of transistors in these amplifiers was likely Krueger's handiwork.
In a 1962 Catalog, Magnatone made an cute sixties-esque move and gave each of the 400 series amps a Greek mythology name. The names were as follows: Jupiter (262), Diana (410), Centaur (413), Clio (415), Athene (435), Mercury (440), Juno (450), Victory (460), and Venus (480).
The new executives at Estey, Green, Knasick, and Souwiene were not guitar guys, in fact, they weren't even musicians. As far as market direction and sales ideas were concerned, they had to rely on the advice of others. Their sales distributor network at the time had a few big players in the accordion market, namely, Ernst Deffner of Deffner/PANcordion/Titano, and Carlo Gasparitti of Imperial. These guys were were selling lots of rebadged Magnatone amps to accordion players, and providing feedback to the Estey Long Island execs that the accordion market was continuing to grow. At the same time, Estey hired Roy Hunt, a kindly older fellow who was an organ and accordion guy, but not so much a guitar guy.
Of course, a guitar and an accordion have the similar output characteristics and a single amplifier design can do both. But from the point of view of the musician, there is another fundamental aspect of an amplifier that plays a huge part in who is going to buy it: styling. The basic styling of the 400 series might have been hip for guitarists in 1957, but by 1963, especially after being re-clad in a brown motif, was staid and conservative. This was so much the case that when engineer Tony Price was hired in 1962, the 400 series was decribed to him by other Estey engineers as accordion amps.
The 400 series was replaced in late 1963 by the 1964 Custom Series, however many of the OEM buyers (Imperial, Titano, Noble, etc) preferred the traditional styling of the 400 series, and Estey continued to build models specifically for those buyers.
for a complete history of Magnatone..