A detail from the JMI amplifiers flyer printed in 1962 (and circulated also in 1963).

This page naturally takes its cue from the page on the Vox AC2. To all intents and purposes the AC4 was simply the AC2 renamed.

One of the first mentions of the AC4 came in a JMI pricelist of October 1961: the "A.C.4. Normal" at £19 and 19 shillings (19 guineas). The other amounts are the hire purchase terms: the initial deposit of £2.0.0, then twelve instalments of £1 15 shillings and 5 pence.

October 1961.

For the first few months of 1962, the AC2 / AC4 does not figure in the pricelists published in the popular music press. Then in May we have the "Vox 4 Watt [amplifier], 2 Input." Price: 19 guineas.

12th May 1962.

But in November it returns, again without specific denomination, as a "Vox 2 Watt [amplifier], 2 Input, vibrato". Price: 19 guineas - as before. A few months later a JMI catalogue (see below) made it clear that the "vibrato" was not the "dynamic Vibravox" of other Vox amps. The "vibrato" of the AC4 was in fact "tremolo".

11th November 1962.

The amplifier remained a "2 Watt" unit through to mid December '62. In early February 1963 mention of the the model name returns - the A.C.4 - 2nd February '63, though it is likely that the name had been introduced earlier. Note the increase in price - to 22 guineas.

2nd February 1963.

In terms of catalogues, the JMI "Choice of the Stars" fold-out from early 1963 embodies the old illustration of the AC2 - beige covering and solid white luggage handle - as the AC/4. The "Precision in Sound" catalogue, produced to accompany the Russell Hotel Trade Fair of August 1963, gives the new format - black vinyl and new plastic handle.

JMI "Sounds of the Stars" catalogue, 1963.

In later 1962, the old-style output transformers gave way to units sourced from Richard Allan, probably best known as a manufacturer of speakers. These were normally stamped "5200" in ink. Some months later, in early 1963, new mains transformers were introduced with taps for a voltage selector - 110v / 230v. The change was evidently made with the American market in view. Tom went to the NAMM show in Chicago for the first time in June - see this page on the Vox AC100 website.

Detail from the JMI "Precision in Sound" fold-out catalogue from August 1963.

Below, some provisional notes on the various changes that took place during production. These will be expanded soon.

SERIAL NUMBERS

AC4

The overview below picks up from the one given on the previous page - on the Vox AC2.

i) ) Late 1961 on. A box with slightly thicker edges introduced. Back of two pieces of birch ply. Still the "island" control panel, the panel itself pink in colour. Grille cloth with diamonds orientated sideways. Larger VOX logo. The electronics were laid out in a more consistent manner from this point - a horizontal ground buss rail introduced, tidier wiring, etc.

Chassis probably assembled for JMI by Triumph Electronics. According to the late Rodney Angell, who worked for JMI in the 1960s as amp tester and service engineer, Triumph had been brought in initially with a view to producing Vox amplifier kits for sale in department stores and so on - a sort of parallel to JMI's "Pacifica" kit guitar, introduced in late 1960. Kit amplifiers - presumably the AC2/AC4 or some version of it - evidently never went beyond the planning stage, but Triumph nonetheless handled production of all AC4 chassis subsequently.

sn. 2211 - AC4, pink panel, sideways cloth.

sn. 2270 - AC4, pink panel, sideways cloth.

sn. 2394 - AC4, pink panel, sideways cloth.

sn. 2408 - AC4, pink panel, sideways cloth.

sn. 2415 - AC4, pink panel, sideways cloth.

ii) From around this point, late 1962, a new taller "thin edged" box comes in. A slider board is provided between the chassis and the speaker (though the chassis does not rest on it). Grille cloth has diamonds pointing vertically rather than horizontally. The control panel sits in a full cutaway, rather than an "island". Assembly of the chassis undertaken by Triumph Electronics in Purley.

sn. 2431 - AC4, pink panel.

sn. 2512 - AC4, pink panel, taller box, diamonds upright.

sn. 2585 - AC4, pink panel, taller box, diamonds upright.

iii) A voltage selector 110 / 230v now provided on the control panel. New transformers supplied by JD Electronics (based in Birmingham). Assembly of chassis still by Triumph. By the time we come to serial numbers in the 2900s, we are well into 1963.

iv) By serial number 3074, vinyl is now black. The control panel remains pink.

Components and assembly

As has already been mentioned, in late 1961 or early 1962, Triumph Electronics, based in Purley, took over production, probably having been brought in at much the same time as the new circuit diagram (below) was drawn up. Triumph continued to make AC2s, then AC4s, through to end of production. Insulated stand-offs and red RTC-branded capacitors are typical of the chassis that Triumph produced for JMI - see for instance the early AC50s (1964) assembled under contract by the company for JMI.

Below, thanks to Martin Kelly, a copy of the circuit diagram for the AC/2 (and AC/4) formerly belonging to Rodney Angell. The sheet, which measures 13" x 8" (old fashioned "foolscap"), is identical to the one designated OS/009 published by Jim Elyea and in circulation elsewhere, but the "OS" number is lacking.

Circuit diagram for the AC/2, no "OS" number.

Components at first were largely the same as those used in earlier amps. By 1963 however, Triumph had begun to use blue Hunts electrolytic capacitors, and Mullard mustard signal caps. Resistors continued to be the white Eries of old. Jack sockets were normally supplied by Re-an Products Limited, based on Burnham Road in Dartford, just a step away from the Jennings Works.

In early 1963, JD Electronics of Birmingham began supplying new transformers, the mains unit with selectable voltage: 110v (for the American market) / 230v for the UK and Europe. The company also supplied transformers for the Vox AC10.

Finished chassis were driven to Dartford Road where they were fitted, sometimes after a time in storage, into cabinets for sale. The speakers wired in at the JMI Works were generally bronze-coloured 8" Rola-Plessey drivers, model number "8C/164", impedance 3 ohms. Serial number plates are hand stamped.

Surviving amps

i) Island control panel, sideways cloth

Serial number 2211 - currently in the USA (?)

The amplifier designated "AC4" on the serial number plate. In the preamp, Daly electrolytic capacitors; and Suflex polyester signal caps (as in AC2s).

Serial number 2270 - currently in the UK

Serial number 2394 - currently in the USA (?)

External shots only. Cosmetic condition good. Picture J. Elyea, p. 126.

Serial number 2408 - currently in the USA (?)

External shots only. Cosmetic condition good. The original wood block footswitch survives, as above.

Serial number 2415 - currently in the USA

Still in a small box.

ii) New taller "thin edged" box with slider board for the chassis

Serial number 2431 - currently in the USA

External shots only. Picture printed by J. Elyea, p. 231.

Serial number 2479

Original speaker and footswitch. In the preamp (fully original), Mullard mustards with the date codes "A2N" and "B2N", respectively first and second quarters of 1962 for their manufacture. One of the Hunts capacitors had "WAH" = 19th week 1962.

Serial number 2512 - currently in Europe

External shots only. Cosmetic condition good. The original wood block footswitch survives, as above.

Serial number 2531 - currently in Europe

Mostly external shots only. Cabinet covered in thin shiny black vinyl. No voltage selector on the control panel. The stamped code on the speaker is "8C/164".

Serial number 2585 - currently in the UK

Serial number 2607

Said to be serial number 2607, J. Elyea, p. 125, but the amp is actually serial number 2067 - pictured on this page.

Serial number unknown - low 2700s

Electrolytics replaced, but otherwise in original order. The Mullard mustard capacitors have date codes "B2N" and "A3N", respectively second quarter of 1962 and first quarter of 1963 for their manufacture. No voltage selector.

iii) Voltage selector phased in from this point

Serial number 2746 - currently in Europe

The speaker, a red label Rola Celestion, may be an early replacement for the original Plessey.

NEW

Serial number 2748 - currently in the UK

Sold some time ago. Good condition externally, original speaker and footswitch present. The amp has a voltage selector.

Serial number 2752 - currently in the UK

A good description of the amp is given by Bill Atkins on this page on the Ampaholics website. No voltage selector. Transformers are "JD Electronics", the earliest definitive appearance so far, but they may have been used in earlier amps.

Serial number 2832 - currently in Europe

Cabinet recovered in red vinyl; mains transformer has been renewed. In the preamp, Mullard mustard capacitors with date codes "A3N" and "B3N" = first and second quarters of 1963. The original Elac speaker has the stamps "8C/164" and "0133433".

Serial number 2907 - currently in the UK

Saved recently from being thrown out. Excellent condition, the original "VOX" hang-tag still tied to the handle. The chassis has components with date codes indicating assembly in early Summer '63: Mullard mustard caps with date codes B2N, A3N and B3N = second quarter of 1962, and first and second quarters of 1963. The main Hunts filter cap has "WHI" = 12th week of 1963. An orange Plessey / TCC cap. with date code November 1963 is likely to be an early replacement for the original Hunts.

Updated

Serial number 2927 - currently in the UK

In the preamp, the blue Hunts cap with date code "YII" = 1st week of 1963; and Mullard mustard capacitors with "A3N" and "B3N", respectively first and second quarters of 1963 for their production. Thanks to Mark for the pictures.

Serial number 2961 (or 2981?) - currently in Europe

As in the case of serial number 2907, original component date codes indicate assembly in early Summer '63: Mullard mustard caps with date codes B2N, A3N and B3N = second quarter of 1962, and first and second quarters of 1963. The main Hunts filter cap has "WHI" = 12th week of 1963. The mains transformer was made by JD Electronics of Birmingham - part number RT.290. JD Electronics also supplied transformers for Vox AC10s.

Serial number 2974 - currently in the UK

External shots only. The Elac speaker is from a later AC4 (hammertone silver, "tin can" magnet cover.

On to the page on later AC4s.