The AC15 was powered by a pair of EL84 tubes, an EF86-driven "Normal" channel, an ECC83-driven "Vib-Trem" channel, and rectified by an EZ81.
The original first-generation AC30 used a GZ34 tube rectifier, three ECC83s (12AX7) for the Normal channel and the tremolo/vibrato oscillator/modulator circuits, one ECC81 (12AT7) phase inverter, and EL34 tubes in the power amplifier circuit.
It is known that it is the 'brilliant' model (or top boost) and it was Edge's earliest amp used to record every U2 album Since the higher output AC30/4 shared its preamplifier design with the lower powered AC15, Vox discovered the high-gain EF86 tube was susceptible to microphonics, or even failure, when exposed to the increased vibration present in this uprated amp.
Vox initially offered a 1×12" version but subsequently introduced the 2×12" AC30 Twin, which solved the volume problem at larger venues.
These AC30 amps were mostly offered in the traditional black Tolex/brown diamond grille configuration, but were also available in limited numbers with purple, red, or tan tolex.
These amplifiers, like all AC30s to this point, were manufactured in Great Britain.
The AC30/6 was now an amp with three channels, each channel having two inputs.
About this time, the "Top Boost" (or "Brilliance") feature became available as Vox's optional addition of a rear panel-mounted circuit that introduced an extra gain stage and tone controls for bass and treble (as opposed to the single "tone" control of earlier AC30s).