Donald L. Bonham was an audio engineer and inventor who's contribution to the Magnatone sound is unequaled. If it weren't for his true pitch shifting vibrato, Magnatone's vibrato would probably just been a tremolo effect like Fender, Gibson, and Ampeg. With Bonham's contribution, Magnatone set the bar for Vibrato.
Bonham lived his entire life in southern California. In the forties, he was a technician for an organ manufacturer, and by the mid fifties, Bonham was an audio engineer at Pacific Mercury when the new Thomas Organ division launched. After several Pac-Merc/Thomas employees broke away and purchased Magna Electronics in early 1957, Bonham was soon hired by Magna to the position of Chief Engineer (March 1957).
Bonham's departure from Magna was prior to 1961. Later, Bonham incorporated the Audio Guild Corporation, building similar amplifiers under his own name Bonham, and for several of the resellers that Estey had been building amps for, like Titano and PANccordion.
Bonham filed several patents. One of his early patents (filed March 1954) was Electrical Vibrato and Tremolo Devices for which the patent office did not grant patent until Aug 1964 (3,146,292). This was the basis of the pitch shifting vibrato that would be used in Magnatone amps. Although it would be refined and improved in later patents, this particular patent sets the paradigm in motion.
Another patent was filed in November of 1956, was 2,933,699: Frequency Control Means For Mono-phonic Tone Generating Oscillator. This was assigned to Pacific-Mercury Television Mfg. Corp.. Pacific-Mercury was Joe Benaron's company and the parent company of Thomas Organ, which Benaron got involved with in 1955. This patent for a tone generator was, no doubt, part of the tone generating circuits of the 1956 Thomas organs. A second patent Bonham filed for Thomas was in January 1957, 2,913,948: Attenuating Circuit For Electric Organ.
Prior to Benaron's financing of Thomas Organ, Pacific-Mercury wasn't involved in musical amplification, only radio and television. It seems like that Bonham arrived at Pacific-Mercury with Thomas George, but Bonham could have been one of Benaron's engineers prior to George and Benaron getting together in 1955.
The vibrato patent Bonham filed in October of 1958, was 100% credited to Bonham (perhaps the ability to own the patent himself was part of what lured Bonham away from Pacific-Mercury. There were several other patents for technology that came out of Pacific-Mercury in those days, but it seemed that Benaron always saw to it that Pacific-Mercury got assignorshop). It was 2,988,706: Vibrato Circuit Comprising a Bridge Having Non-Linear Impedance Elements filed in October 1958 that patented his vibrato invention and thus gave the Magnatone its magic vibrato sound.
Next he filed Electrical Music System in March 1959 which was granted in December of 1964. This patent was a continuation of his vibrato inventions. It was meant to provide a method to produce an improved vibrato by reducing the effect of wandering pitch on reiterated tones (3,160,695 and 3,083,606). This was the patent for the stereo vibrato used in several Magnatone amps including the 280, 480, M14, and the M15 amps.