In order to meet growing demand, in mid 1962 JMI contracted Burndept Electronics, based in Erith, to assemble batches of chassis in addition to those already being assembled by Westrex.

The two companies were not only responsible for making the chassis (the metalwork), but populating them with components, checking and testing, and so on - in other words providing finished, working electronics.

One of a huge series of adverts placed by Burndept in local Dartford newspapers in the 1960s, this from June 1961. The jobs were based in the West Street Works in Erith, which JMI later took over (in late 1964). Whether the rates were the same in the late autumn of 1962 when Burndept began producing AC30 chassis for JMI is hard to say for certain - but they were presumably not too far off. The basic conditions were 42 hours per week (which held true also for 1962); £7 8s 2d per week, which equates to around 3s 6d (3/6) per hour.

Burndept-made chassis are identifiable in several ways: early on by the use of Woden transformers with green coloured shrouds (Westrex used Haddon and Albion); small cut-outs for the cage nuts in the aluminium preamp upright; and by the presence of stamped chassis numbers.

A Burndept-made chassis from early to mid 1963. Green-shrouded Woden transformers, and a chassis number stamped in front of the output transformer.

Below, details showing the cut-outs for the cage-nuts in the aluminium preamp upright - a useful indicator (if there are no others) that a chassis was produced by Burndept. Westrex-made chassis do not have them.

Details from serial number 6097. The cut-outs for the aluminium preamp upright marked with arrows. These cut-outs do not figure in the chassis made by Westrex.

Dolly Clark, who oversaw the assembly benches at Burndept, is said to have ruled with a rod of iron to keep production figures up. According to the late Rodney Angell, who tested AC30s before they were sent out into the world from Dartford Road, recalled that Burndept-made amps occasionally suffered from dry solder joints, a consequence of the speed at which the chassis were assembled.

Westrex, in contrast, checked its solder joints, marking them with red dye to indicate that they had indeed been checked. Westrex-made chassis were not numbered though. Nor for that matter were those produced by Burnham Engineering (based in Dartford), which supplied a large proportion of the metalworking required by JMI from 1957 through to the winter of 1961 (the last of the AC30/4s). The chassis made by Burnham were populated with components, however, at 115 Dartford Road.

Initially, Burndept stamped its numbers on top of the plinth in front of the output transformer. From early to mid 1963, the stamps were made on the aluminium preamp upright, beneath the voltage selector. The sequence began at number 01000. The change of position - stamping on the aluminium preamp upright - probably came in at chassis no. 02100.

From around chassis number 3000 in 1964, colours were brushed on to indicate voicing (Treble, Bass, Top Boost) - see this page.

In late 1966 or early 1967, the position of the chassis number was changed again - to the left hand side of the preamp chassis above the speaker terminal block, as in AC50s and AC100s.

In 1968, a new sequence of numbering was introduced, beginning at 25000. This ran to at least 25151.

While chassis were certainly stamped in order, it is not clear yet whether they were assembled in order on the Burndept work benches. Evidence gleaned so far suggests that they were not.

Also to add that chassis, once finished, were neither stored in order, sent to JMI in order, nor fitted into AC30 cabinets in any order when the time came for an amplifier to be made up for sale.

One cannot date AC30s therefore by these numbers. The same is true for the other models of amplifier chassis - T60, AC10, AC50, and so on - assembled by Burndept for JMI.

Below, pictures to illustrate the location and format of the Burndept stamps. These will be added to in due course.

(1) - winter 1962 to late 1963

Chassis numbers 01000 - around 02100 (?)

The 29th chassis stamped with a number by Burndept, the lowest Burndept chassis number encountered so far. The serial number plate unfortunately has parted ways with the amp.

Detail of serial number 6097, below. Chassis numbers begin at 1000, but they were not used in any particular order.

The designation "AC.36" was simply the early short-hand for AC30, six inputs. As production proceeded, the format became "AC30/6", the earliest known instance currently being 01518, below.

Chassis number 1518. Serial number unknown, probably in the high 6000s or low 7000s.

The 945th chassis *stamped* by Burndept. Not the 945th completed. The number is stamped on the plinth. The serial number of the AC30 is unknown

The 1000th Burndept-made chassis, number still stamped on the plinth. The serial number of the AC30 is unknown. Its Woden transformers have date codes "JU" and "KU" = September and October 1963. Thanks to Robert for the picture.

(2) - late 1963 to late 1966

Chassis numbers 02100 (?) - around 12000(?).

The highest number currently known (Nov. 2020) in this position - on the right-hand side of the preamp - is AC30/6 SER. No. 11371: AC30 Super Twin serial number 5031.

Chassis number 02238, stamped on the aluminium upright. AC30 serial number 9434.

Chassis number 11371, AC30 Super Twin serial number 5031.

(2a) - early 1964

Chassis numbers 3000 (?) - around 3100. Four digits only.

Probably only around one hundred chassis stamped in this way. Number 3094 is the highest encountered so far. Most of the amps appear to be Treble models. One rider is a number that looks like 03083 - but that could be 03903 (hard to tell definitively from the photo).

Chassis number 3018, serial number unknown, probably in the low-ish 11000s though. Thanks to Glen Lambert for the picture and for pointing out the existence of this four digit run.

(3) - late 1966 to early 1968

Chassis numbers 12000 - around 14500.

The lowest number currently known (Nov. 2020) on the left-hand side of the preamp is the one below, 12021. The serial number plate of the amplifier - an AC30 Twin - is missing. The highest known at present is 13622.

Chassis number 12021, stamped on the left-hand side of the preamp.

(4) - 1968 - NEW SEQUENCE

Chassis numbers 25000 - around 25200 (?)

In 1968, a new AC30 chassis numbering sequence was begun, presumably at the request of JMI, beginning at 25000. Chassis number 25139 is Super Twin serial number 5596; chassis number 25251 is now in a box from 1965.

Super Twin, serial number 5596; chassis 25139. Woden transformers with February and March 1968 date codes.

Chassis number 25151. Wodens with 1968 date codes; Mullard mustard capacitors with 1967 and 1968 codes.

The initiation of this new sequence may have been devised for accounting purposes. In December 1967, Royston Industries, the umbrella company that held controlling interests in JMI, Burndept, and Heslop and Co. (which made cabinets for JMI) failed. The official receiver was called in. JMI and Burndept continued trading, but under much reduced circumstances. At the end of April 1968, JMI finally came to an end. Its stock for the most part was bought in by the new venture set up by Reg Clark and Cyril Windiate to take the "Vox" name forward - "Vox Sound Equipment Limited" (from June 1968).

Indications are therefore that at least 151 AC30s were produced by JMI in 1968. Whether these were actually sold by JMI is unknown at the moment. It is possible that many passed to VSEL to be sold in the second half of the year.