The AC.6 was one of those amps not much illustrated by Jennings. Our first reference to it comes in March 1960, priced at 19 guineas. To date, no promotional picture has come to light, only notes of its price, which increased at intervals with the rest of the JMI range: in April 1960, ie. soon after its appearance, it became 25 guineas (£26 and 5 shillings), and in the autumn of 1961, 27 guineas (£28 and 7 shillings). In early 1962 it disappears from view entirely.

From its inception through to late 1960, the AC.6 was evidently a simple single-channel 6 watt amplifier, with tone and volume controls only - what we would call a "practice" amp these days, though nothing of the sort was ever ventured at the time. In late 1960, however, the decision was taken to equip the model with "vibrato", presumably to update it in relation to the new two-input AC.2 (which had vibrato as standard) and the AC10 "Throwback". As can be seen in the right-hand image below, the new circuitry was fixed on an aluminium bracket to the inside of the AC.6's back panel, the control knob (for the setting of the vibrato's speed) protruding through the board dead centre, where the serial number plate on the earlier amps would normally be:

On the left, an early AC6, serial number 1012, no "vibrato". On the right (picture from J. Elyea, p. 403), an example with vibrato, the circuitry fixed to its back board, control knob protuding through the centre of the panel.

Vox AC.6, "vibrato" module on the back panel. The circuit, driven by an ECC83 (12AX7), is the same as that of the AC.2.

The same type of approach was taken in the case of the AC10 "Throwback" - an aluminium assembly for the circuitry, and control knob on the back panel:

AC10 Throwbacks, late 1960. These appeared in the Jennings line-up at the same time as the AC2 and AC6 with "vibrato".

Mention of "vibrato" seems first to have been made in relation to the AC.6 in November 1960 and retained through to close of play:

Late 1961 / early 1962, one of the last occurences, if not the last.

Insofar as production is concerned, it looks as though initial batches made by Jennings sold very, very slowly, a result no doubt of the relative lack of promotion on the one hand and on the other the model's old-fashioned (TV Front) appearance, old fashioned at least where 1961 was concerned. The AC2, with its new split-front cabinet, sold exceedingly well in comparison, in many respects presenting a better and cheaper - much cheaper - alternative to the AC.6. And it was naturally the AC.2 rather than its older brother that appeared in the Jennings amplifiers brochure of Spring '61.

AC.6 serial number 1012. Thanks to Martin for the picture.

Serial numbers it should be said began at 1000. Of the five or so AC6s currently known, only two retain their plates.

Assembly

Although nothing is known definitively at present about the design and prototyping process, indications are that production of the AC.6's chassis was contracted out initially to Westrex (in North London). Red dye to indicate that a solder joint had been checked (by an inspector) is apparent throughout many of the early amps and typical of Westrex. Also typical is the coloured sleeving for flying leads.

AC.6 serial number 1012, red dye clearly visible on the Re-an jack sockets (and elsewhere in the chassis).

Transformers are likely to have been sourced in early 1960 from Richard Allan. The output tranformer is part no. 4560, the mains 3634 (?) with voltage taps for 200v, 230v, and 250v, presumably simply to make provision for varying voltages in the UK. Some months later one finds Allan output transformers in AC.2s, part no. 5200. Chassis were mounted in their cabinets (at Dartford Road) on a slide in / slide out board, much as one finds later on in Vox AC10s and AC30s. The speaker: normally a grey-framed 8" Elac 8R/99.

AC.6 serial number 1012, upper chassis.

The valves employed in the circuit were an ECC83, EZ80 rectifier, and EL84, controls being Tone and Volume, the former standing in front of the ECC83 (on its grid), an old-fashioned and potentially noisy arrangement. A negative feedback line (to dampen any oscillation) runs from the ECC83 to one leg of the output transformer.

As mentioned above, the "vibrato" circuit (really tremolo) introduced in late 1960 was borrowed from, or at least worked up in parallel with that of the AC.2, which had the effect as standard from the outset and a control knob on its panel to regulate it.

A detail of the tremolo circuit for the AC/2 from a sheet drawn up by John Bell in December 1961 for Triumph Electronics. No "OS" number is given. The circuit is identical to the one used for the AC.6 illustrated further up tbis page.

That surviving sheets for the AC.6 show only the main circuit (thumbnail towards the end of this page) is just one of those things. Presumably at one time there will have been an ancillary sheet for the AC.6 showing the tremolo (as expressed in the image above) and how to wire it in. This was certainly done for the AC10 and AC15 in 1960.

Layout and wiring-in sheet for Vibravox no. 2 for the AC10 and AC15, copy from Rodney Angell. Rodney saved the original sheet (which is larger than standard) from destruction at the Vox Works in Erith when "Vox Sound Equipment Limited" folded in late 1969.

Select documents

March 1960, 19 guineas. In April the price went up to 25 guineas. The other amplifiers in view are the AC10 without tremolo, AC10 with tremolo, and the AC15 and AC30.

Yardley's, Birmingham, May 1960, an AC6 in company with an AC10 without tremolo (at 29 guineas). This is the only instance that has so far come to light of a shop advert for an AC6 outside London.

November 1960, two versions of the AC2 (4 watts, single and double input), and the AC6.

April 1961, AC2 and AC6.

JMI typescript pricelist of October 1961, giving hire purchase terms. "Normal" simply indicates "not Bass".

OS/006, circuit diagram for the AC6 dated 8th December 1959.

On to the AC2, late 1960 to 1963.