Vox, AC-30 Super Twin Head - 30 W and 2x12" AC-30 cabinet, 1966 - Sully Chamand


AC-30 Super Twin Head - 30 W and 2x12" AC-30 cabinet
The Story Behind


About the Amp (from Wikipedia):

The Vox AC30 is a guitar amplifier manufactured by Vox. It was introduced in 1958 to meet the growing demand for louder amplifiers. Characterised by its "jangly" high-end sound it has become widely recognised by British musicians and others.

The Vox AC30 was originally introduced in 1958 as “big brother” for the fifteen watt (15 W) AC15 model at Hank Marvin's request because the AC 15 was not loud enough with the screaming fans at Cliff Richard concerts., Vox's original flagship amplifier. 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, or AC30/4, had only a single 12 inch Goodmans 60 watt speaker in a "TV Front" cabinet, as opposed to the later, conventional twin 12” speaker configuration. The AC30/4 sported two channels with two inputs – hence the “4” in the model name, and had a single tone control in it as well. The amplifier used a GZ34 tube rectifier, three ECC83s (12AX7) for the Normal channel and the tremolo/vibrato oscillator/modulator circuits, and one ECC81 (12AT7) phase inverter, and it had EL34 tubes in the power amplifier circuit.[2]

This first generation of AC30s were housed in "TV-front" cabinets, much like the early to mid 50s tweed Fender amps. However, the amps sported a thin white covering ("Rexine") with a small printed diamond pattern and larger diamond pattern grill cloth. The EL34 powered AC30 was short lived, and a new AC30 version appeared in late 1959. This second generation AC30/4 was powered by a quartet of EL84 (6BQ5) power tubes, making it truly a doubling of the AC15 circuit, and it also carried over the AC15's preamplifier, which included the EF86 pentode in its "Normal" channel. However, this preamplifier, coupled with the AC30's increased output over the AC-15, revealed a reliability issue. 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 1X12" version and subsequently introduced the 2X12" AC30 Twin, which solved the volume problem at larger venues. The first AC30 Twins used Goodmans Audiom 60’s 15 Watt Speakers, followed by Celestion G12 Alnico speakers.

By 1960, Vox had forsaken the more conservative TV-front look for the now legendary cabinet design that has remained largely unchanged since 1960. The new cabinets featured a different covering known as fawn Rexine, which was a sort of beige leather-cloth with a subtle printed grain. The front baffle was now divided by a thin gold-toned strip with the upper valence covered in fawn Rexine, and the lower grille covered in brown diamond cloth. Ventilation was provided by three small brass vents on the top of the cabinet, and the TV-front's single suitcase type handle was replaced with three leather straps.

To cure the unreliability issues Vox introduced the AC30/6 in 1961 and redesigned the troublesome EF86 tube circuit, replacing it with an ECC83 (12AX7). 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). The unit became so popular that its features were soon incorporated in newer AC30/6 models, and the controls moved from the rear panel to the control panel. Vox AC30/6 amplifiers from around 1963 had already implemented the top boost, and therefore had 3 tone controls. People began to refer to these amplifiers as AC30TBs.[3] Later on, Vox also offered additional versions of the AC30 unit. In addition to the "Normal" version without the Top Boost, and the Top Boost version (which was a Normal version with the "Brilliance" unit added), Vox, with slight circuit modifications, created two more versions that were “voiced” in Brilliant (Treble), and Bass styles. Of all the different models that came around many consider the AC30 "Super Twin" to be the ultimate AC30, with a "trapezoid" shaped head and separate speaker mounted on a trolly (Vox Story, Peterson & Denny 1993) and Vox showroom web site.

By the middle 60's, the various combo amp versions of the AC-30 started to consolidate into one model.

Cosmetically, brown Vox grill cloth was being phased out in favour of black. The predominant control panel color was now grey. Three injection moulded, black plastic Vox logo handles and three metal Vox logo air vents were mounted on the top of the amplifier. The amps were covered in "basket weave" Vinhyde, and eight "one-pin" corners were standard. A new rotary voltage selector switch replaced the former "removable plug" style system. The chassis was completely hand wired.

Perhaps the most important change was moving the Bass and Treble controls of the rear mounted "Top Boost" circuit to the top control panel. The "Top Boost" circuit would no longer be an optional, added-on circuit, it would be a standard feature on AC-30 amps. As a result, the Bass and Treble controls would no longer protrude from a rectangular hole in the vinyl covered upper back panel of the amplifier.

The AC-30/6 Twin had three channels, Brilliant, Normal, and Vib-Trem. The Bass and Treble controls only affected the Brilliant channel. The Cut control affected all three channels.

The Vib-Trem channel offered a choice between vibrato (wavering pitch) and tremolo (wavering amplitude). A rotary, three position Speed switch adjusted the the rate of modulation. An egg shaped single button foot switch operated the effect.

Two 8 ohm 12" Alnico Silver Celestion G12 speakers were standard. The typical Celestion from this era had wire connecting lugs mounted to a card board tag strip that was riveted to the speaker frame.

Based on the Vox AC-30 the AC-30 "Super Twin" Amp Head is nevertheless somewhat different:

The original version of the AC-30 Super Twin head used a standard AC-30/6 amplifier chassis installed into a rectangular head cabinet. From 1961 through 1963, most of these amps were covered in fawn (or light tan) vinyl. Amps produced in 1963 would most likely have smooth black vinyl while those produced from 1964 through 1967 would have black basket weave vinyl. The front panel would most commonly be covered in brown Vox diamond grill cloth and feature a small. -V-O-X- logo.

When introduced in 1961, the AC-30 Super Twin was offered by Vox primarily as a bass guitar amp. Vox felt that separating the head from the speaker cabinet would improve dependability over the combo version of the amp by isolating the chassis from the direct vibrations emanating from the speakers.

The AC-30 "Super Twin" Speaker Cabinet

The Super Twin speaker cabinet was an adaptation of the original AC-30 combo amp cabinet, less control panel cutout. The number of handles was reduced from three on the combo amp to one on the speaker cabinet.

Vox product catalog descriptions from the early to mid 1960's indicated that Super Twin speaker cabinets normally had closed backs, or were "pressurised," using Vox marketing speak. Closed backed cabinets enhance low end response, thus improving the performance of the AC-30 for bass guitar. However, not all AC-30 Super Twin speaker cabinets had closed backs. Some shared the same split open back configuration as the combo amp.

Two 8 ohm Celestion/Vox 12" Alnico speakers, wired in series to 16 ohms, powered the cabinet.

The Redesigned 1965 - 67 of the AC-30 "Super Twin" Amp ramped up the appeal of the AC-30 Super Twin amp series in 1965 by adding an optional chrome plated tubular steel swivel trolley, installing Top Boost circuitry in the main control panel, incorporating a reverb circuit and converting the head cabinet to a trapezoidal, or "slant sided" shape. This new amp was known as the AC-30 "Super Reverb Twin."

David Petersen and Dick Denney, the authors of "The Vox Story," call it "the ultimate in AC-30 development."

This amp has been the live gear for Sully Chamand when in Paris. It has been used among others in the Fet Kaf Sully et les Chamanes et René Lacaille concert 18 décembre 2011.

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