The amplifier chassis's were assembled by Triumph Electronics, one of VOX's sub-contractors, starting in 1965 as was many of the AC-50's and most of the AC-100's chassis.

The numbers attached after the "7" or "4" indicated the amplifiers' wattage. Models with a "7" in the name were a lead version while the "4" denotes a bass model.

All the "7" & "4" series amplifiers were hybrid which means that they had a solid state pre-amp and a valve output section. As with most VOX products, the exception to this is the 705 and 710 which were totally valve. The "7" and "4" pre-amp section looks remarkably like the Thomas Organ pre amps and probably Thomas was, at least marginally, responsible for its design.

The 7120, in particular, is notable because of its association with The Beatles. They had toured with custom 7120's and 4120's in 1966 and utilized them in the recording of "Revolver" and "Sgt. Pepper."

The Beatles were also presented with a set of 7200's which were custom 200 watt versions of the 7120. These amplifiers featured six KT88 output valves and were so heavy that it took two people to carry them. The 7200 amplifiers were never utilized by The Beatles publicly nor in the studio. These 7200's were intended for The Beatles' 1966 United States Tour, but Thomas Organ raised a stink and insisted that The Beatles use only US made solid state models.