The Pro Series was introduced as a thrid line of amplifiers, joining the premium professional Custom Series, and the student Starlite series of amplifiers. The Pro Series was designed specificially for rock guitarists and bassists. The Custom Series made for fine rock-n-roll amplifiers, but rock musicians favored loud amps, and the $$/WATT of the Customs was too high for most young rock musicians. I also suspect that a design criteria of the Pro Series was that it needed to be easily stacked in a station wagon or panel van (not a characteristic of a Custom M-series amp).
Production began in the fall of 1965 at the Torrance Facility, and
were in showrooms as early as November 1965.
After Estey moved to Harmony in 1966, production continued for a
few more years. There was no confusion
in the marketing department about this product line, it was for guitar and
bass. Gone from sales literature was the word "accordion".
With the black and silver motif, piggy-back and combo amp designs with front facing control panels, Estey wanted to leave no doubt in anyone's mind who the target audience was (prospective Fender amp buyers).
The circuits continued to be well engineered, although Bonham's F.M.vibrato was dropped in favor of the less expensive, simpler ampeg style vibrato. 6CA7's and 7189A's were still used in the output sections.
The amps did not enjoy tremendous success perhaps due in part to the fact they weren't a low cost alterative to Fenders amps, they were priced about the same, or higher. The list price of a MP5 head and RS-12 2x12" cabinet was $660 ($440 + $220), whereas a comparable Fender Bandmaster (or Bassman) was $100 less.
One very innovative feature of the Pro Series was the electroluminescent strip that back lit the control panel. Here is what Estey Chief Engineer Tony Price had to say about this feature: "The illuminated face plate used a newly developed electroluminescent strip that could be dimmed. It was kind of a gimmick, but musicians often said they had trouble seeing the amp controls on a dark stage. This seemed to solve the problem, without producing bright light that would bother others."
Also, see neon bulbs for an up-close look at the vibrato oscillators on this series amp.
for a complete history of Magnatone..