The JMI Vox AC10RT 3x10" Combo Amplifier

The story surrounding the Vox amp featured on this web page is truly enigmatic. This is the tale of a Vox amp model whose history is shrouded in mystery. Various clues relating to cosmetics (such as basket weave covering, black Vox grill, slender black vents, Vox logo strap handle) suggest that this model would likely have been produced in the latter JMI period (1964-1966) but this amp made no appearances in either Vox catalogs and price lists from that era. As only a small handful of these amps have surfaced, production numbers must have been very limited. As none of the these amps seemed to have a model ID or serial number plate, there is no way to know what Vox actually called this model. As a result, I will simply name it the AC10RT 3x10"combo. The "RT" stands for reverb and tremolo.

Chassis and Circuitry
JMI introduced a new guitar amplifier design on JMI schematic "OS/026 AC10 Super Reverb Unit," dated January 27, 1964. While the AC10 Super Reverb Unit chassis was the beating heart of the AC10RT 3x10" amplifier, the chassis would also be included in the Vox AC10SRT amp head and the JMI Domino Super Reverb Piggy back amplifiers.

The preamp circuitry of the AC10 Super Reverb Unit bore little resemblance to the original and namesake Vox AC10 circuit documented on JMI schematic "OS/008 AC/10 Amplifier No 3," dated September 9, 1960. The original AC-10 design from 1960 had two channels while the AC-10 Super Reverb unit had only one. While the preamp circuit of the 1960 AC-10 utilized esoteric ECF82 and EF86 tubes, the 1964 "AC10 Super Reverb Unit" preamp was powered by more conventional 12AX7 and 12AU7 tubes. The only effect in the original 1960 era AC-10 circuit design was tremolo. The 1964 era AC-10 revision added reverb. The "AC10 Super Reverb Unit" and the original "AC/10 Amplifier No 3" circuits were produced concurrently by Vox in 1964 and 1965.

Like its bigger brother, the AC-15, the AC10 Super Reverb Unit power amplifier section was powered by two EL84 power tubes in a Class A, cathode biased, no negative feedback amp circuit. A close comparison of the AC10 Super Reverb Unit schematic (OS/026) and AC15 schematic (OA/031) reveals that both models have similar power amp circuitry, suggesting that the AC10 Super Reverb Unit chassis is actually capable of producing about 15 watts RMS.

Click here to visit the AC10 Super Reverb Unit Chassis - A Look "Under the Hood" webpage in the Vox Showroom.

The Vox AC10RT 3x10" and the Vox LW30 (Light Weight 30) watt combo amps shared the same cabinet and three 10" speaker complement.

Introduced in 1964 to mixed reviews, the Vox LW30 shared its chassis with the Vox T.60 bass amp. JMI hoped to entice customers by offering the solid state Vox LW30 amplifier as a light weight alternative to the relatively heavy AC30 amplifier. Unfortunately, a design flaw in the LW30 and the T.60 circuit design made them subject to electronic failure, causing a surge in warranty claims for JMI and customer satisfaction to suffer.

The AC10 Super Reverb Unit chassis could be installed into the LW30 cabinet with very little rework by JMI, making it easy and cost effective to for Vox to introduce the AC10RT 3x10 amplifier.

The design of the AC10RT 3x10 and LW30 cabinets strayed away from traditional Vox design in several ways. While the top ⅓ of the front panel of a typical Vox combo amplifier was covered with vinyl and the lower ⅔ was covered with grill, the AC10RT 3x10 featured a front panel that was fully grilled from top to bottom. The location of the control panel was relocated from the traditional horizontal location at the top of the amp to a vertical position on the upper rear of the AC10RT 3x10.

Control Panel
Many amps equipped with the AC-10 "Super Reverb" chassis, such as those shown in the pictures shown at left, were equipped with a traditional (and separate) anodized aluminum control panel. While gray anodized control panels seem to be more common, red panels were also produced. However, some AC-10 "Super Reverb" chassis do not have an anodized control panel. The control panel nomenclature on these amps was silk screened directly to the leading edge of the aluminum chassis as a cost saving measure.

The unusual 3x10" speaker complement of the Vox AC10RT was reminiscent of the Fender 5E7 and 5G7 Bandmaster 3x10" amps from the late 1950's.

The Vox AC10RT was equipped with three Goodmans 10" stamped frame speakers with alnico magnets. An impedance value of 15Ω was imprinted on the rim of each speaker (see photo at left). As the trio of 10" 15Ω speakers was wired in parallel, a total load of 5Ω (15Ω ÷ 3 = 5Ω) was presented to the output stage of the amplifier.

AC10RT 1x10
There is one last twist to the AC10RT 3x10 story. A Vox enthusiast from Sweden sent me the two photos at bottom left of a 1x10 version of the AC10RT combo amp, making it a perfect competitor to the popular Fender Princeton Reverb. He confirms that the baffle board and single 10" Elac speaker are original.

Vox AC10RT 3x10" Combo Amp
Output Power ~15 watts
Tube Complement 1 x ECC83, 3 x ECC82, 1 x EZ81, 2 x EL84
Control Panel two inputs,
one volume,
one tone

one tremolo depth
one tremolo speed
one reverb
Speakers Three 10" Goodmans speakers
Dimensions 24" x 20.5" x 11"
Accessories Cover, Foot pedal.


The VOX Showroom!

Photos and editorial content courtesy Gary Hahlbeck, North Coast Music

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