The 7120 Speaker Cabinet
The 7120 head is one of the rarest items produced by Vox, only to be exceeded in rarity by an original 7120 speaker cabinet. North Coast Music produced a handful of these 7120 cabinets and trolleys in the past ten years, including those shown on pages 468 and 471 of "Vox Amplifiers - The JMI Years" by Jim Elyea. Only recently did a original 7120 cabinet surface.
At exactly 41 3/4" wide x 30" tall x 13" deep (less hardware), the original 7120 speaker cabinet was slightly larger than the AC-100 Super Deluxe cabinet. The upper and lower back panels were both 10" tall and 1/2" thick. The 7120 speaker cabinet was oriented horizontally, unlike the vertically oriented AC-100 Super Deluxe.
While stripped of its vinyl and grill, this original 7120 cabinet confirmed the unusual baffle placement of three Celestion T.1225 12" speakers across the bottom and a fourth in the upper center. Two Goodmans Midax horns were located in the upper left and upper right corners of the baffle. A 2 uf oil filled crossover capacitor isolated each Midax horn from frequencies below 3500 hz.
The UL Series amps, including the 7120, abandoned the use of XLR jacks and plugs for external speaker connection. The 7120 head and speaker enclosure adopted standard 1/4" speaker jacks.
Many have discussed the unusual layout for the 12" speakers. Some have suggested that placement of three 12" speakers across the bottom of the 7120 baffle improved the stability of the cabinet in the swivel trolley. I suspect that this may only be part of the story.
JMI recognized that their number one client, the Beatles, would be using this behemoth of an amplifier in their 1966 world tour. John Lennon and George Harrison had recently started to perform with Epiphone Casino guitars. The Epiphone Casino did not have a solid block under the pickups, making the guitar easily susceptible to feedback from an amplifier. The massive 120 watt RMS output of the 7120 would make the feedback problem even worse.
While only an observation, I have often wondered if the horizontal cabinet orientation and the placement of three of the 12" speakers across the bottom of the 7120 cabinet might minimize feedback with a guitar like the Casino. Three of the four 12" speakers were just above the floor, well below the height of the guitar.
My thanks to Mark Vacquer for sending the photos and accurate dimensions of his original 7120 enclosure.